14112008

Why you (scientists) should start blogging

Enrohttpwwwcafe-sciencesorg

Swiss Center for Affective Sciences Geneva Switzerland 1

Curriculumbull Engineer in Agricultural SciencesbullMSc in Social Studies of Sciencebull Blogger since 2003 as ldquoEnrordquo science blogger since 2006bull Co-founder of the science blogs community ldquoCfeacute des sciencesrdquobull President of the French association ldquoCfetiers des sciencesrdquo

2

Find the blog post

3

This evening I am nose deep in the middle of the new issue of The New England Journal of Medicine The journal contains a very interesting synopsis on the presidential candidates views on reproductive freedom If you completely ignore the rest of my post (but you wont because its going to be totally hot) read the reproductive freedom articleBut what has Dr Isis all a twitter is actually a piece of correspondence from Swedish researchers Imre Janszky and Rickard Ljung entitled ldquoShifts to and from Daylight Saving Time and Incidence of Myocardial Infarctionrdquo Janszky and Ljung present a very intriguing data set Its just a shame their interesting data are confounded by their crappy interpretationClearly Dr Isis (hellip) must have been too busy pouring herself a cocktail or staring at her hotness in the mirror to notice their data showing that sleep deprivation was highest in women and people under 65

It has been postulated that people in Western societies are chronically sleep deprived since the average sleep duration decreased from 90 to 75 hours during the 20th century Therefore it is important to examine whether we can achieve beneficial effects with prolonged sleep The finding that the possibility of additional sleep seems to be protective on the first workday after the autumn shift is intriguing Monday is the day of the week associated with the highest risk of acute myocardial infarction with the mental stress of starting a new workweek and the increase in activity suggested as an explanation Our results raise the possibility that there is another sleep-related component in the excess incidence of acute myocardial infarction on Monday

Find the blog post

3

This evening I am nose deep in the middle of the new issue of The New England Journal of Medicine The journal contains a very interesting synopsis on the presidential candidates views on reproductive freedom If you completely ignore the rest of my post (but you wont because its going to be totally hot) read the reproductive freedom articleBut what has Dr Isis all a twitter is actually a piece of correspondence from Swedish researchers Imre Janszky and Rickard Ljung entitled ldquoShifts to and from Daylight Saving Time and Incidence of Myocardial Infarctionrdquo Janszky and Ljung present a very intriguing data set Its just a shame their interesting data are confounded by their crappy interpretationClearly Dr Isis (hellip) must have been too busy pouring herself a cocktail or staring at her hotness in the mirror to notice their data showing that sleep deprivation was highest in women and people under 65

It has been postulated that people in Western societies are chronically sleep deprived since the average sleep duration decreased from 90 to 75 hours during the 20th century Therefore it is important to examine whether we can achieve beneficial effects with prolonged sleep The finding that the possibility of additional sleep seems to be protective on the first workday after the autumn shift is intriguing Monday is the day of the week associated with the highest risk of acute myocardial infarction with the mental stress of starting a new workweek and the increase in activity suggested as an explanation Our results raise the possibility that there is another sleep-related component in the excess incidence of acute myocardial infarction on Monday

This evening I am nose deep in the middle of the new issue of The New England Journal of Medicine The journal contains a very interesting synopsis on the presidential candidates views on reproductive freedom If you completely ignore the rest of my post (but you wont because its going to be totally hot) read the reproductive freedom articleBut what has Dr Isis all a twitter is actually a piece of correspondence from Swedish researchers Imre Janszky and Rickard Ljung entitled ldquoShifts to and from Daylight Saving Time and Incidence of Myocardial Infarctionrdquo Janszky and Ljung present a very intriguing data set Its just a shame their interesting data are confounded by their crappy interpretationClearly Dr Isis (hellip) must have been too busy pouring herself a cocktail or staring at her hotness in the mirror to notice their data showing that sleep deprivation was highest in women and people under 65

It has been postulated that people in Western societies are chronically sleep deprived since the average sleep duration decreased from 90 to 75 hours during the 20th century Therefore it is important to examine whether we can achieve beneficial effects with prolonged sleep The finding that the possibility of additional sleep seems to be protective on the first workday after the autumn shift is intriguing Monday is the day of the week associated with the highest risk of acute myocardial infarction with the mental stress of starting a new workweek and the increase in activity suggested as an explanation Our results raise the possibility that there is another sleep-related component in the excess incidence of acute myocardial infarction on Monday

One interesting observation from the studies of entrainment by skeleton photoperiods is the bistability phenomenon A full photoperiod will entrain the biological clock no matter how short or long is the photoperiod ie the duration of the light portion of the light-dark cycle Thus LD 123 LD 321 LD 618 LD 816 LD 1014 LD 1212 LD 1410 LD 168 LD 186 LD 213 and LD 231 are all equally likely to entrain a clock On the other hand with skeleton photocycles photoperiod matters The biological clock prefers short photoperiods to long photoperiods Thus when exposed to a skeleton photocycle that attempts to entrain to a cycle mimicking a long photoperiod the rhythm will instead reverse the night and day (often with an abrupt phase-jump)

Seasonal variations influencing circadian behavior can be simulated by applying different experimental photoperiods A photoperiod is described by the ratio of light to darkness during a 24-hour cycle Under laboratory conditions summertime light conditions are typically represented by cycles of 18 hours light and 6 hours dark or of 14 hours light and 10 hours dark (LD 186 and LD 1410 respectively) whereas winter light conditions are mimicked by an LD 618 cycle or an LD 1014 cycle In photoperiod experiments the external time of the Zeitgeber rhythm is specified as ExT (External Time) with ExT12 corresponding to the middle of the light-phase Most laboratories use a rapid transition from light to dark and from dark to light and apply the same wavelength range and light intensity during the whole light period However this does not truly reflect natural lighting conditions

From one to many

6

A personal tribune

From one to many

8

A personal tribune

A personal tribune

A personal tribune

From one to many

10

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

12

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

14

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

Reader

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

From one to many

6

A personal tribune

From one to many

8

A personal tribune

A personal tribune

A personal tribune

From one to many

10

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

12

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

14

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

Reader

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

From one to many

8

A personal tribune

A personal tribune

A personal tribune

From one to many

10

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

12

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

14

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

Reader

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

From one to many

10

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

12

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

14

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

Reader

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

From one to many

12

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

From one to many

14

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

Reader

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

From one to many

14

A personal tribune

A personal tribune

A personal tribune

Reader

Reader

Reader

Reader

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

17

What does it mean for research

Institutionspeers

Certified knowledge instruments

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

LETTER TO THE EDITOR

A Toxic Mutator and Selection Alternative to the Non-MendelianRNA Cache Hypothesis for hothead Reversion

Lolle and colleagues observed frequenttrue reversion of hothead (hth) mutationsof Arabidopsis thaliana whereby up to 10of the progeny of self-pollinated homozy-gous hthhth mutants carried a grandpa-rental HTH allele (Lolle et al 2005)Instability was not limited to the HTHgene hth mutants displayed conversionof genome-wide polymorphisms to thegenotype of a recent ancestor The possi-bility that a mutator phenotype causedindiscriminate changes thereby increasingthe reversion rate of hth was discountedbecause reverted HTH alleles showed noadditional nucleotide changes whereas 50to 100 changes per sequenced allele wouldbe expected from the 5 hth reversionrate These genetic instabilities were inter-preted as a memory of a past genotypicstate A cache of double-stranded RNAfrom the previous genotype was proposedwhich at times of stress corrects mutatedsites in a template-directed manner Theexistence of an alternate reserve genomeappears consistent with the data and wouldnecessitate a revision of our theories ofheredity Two recent commentaries on thisdiscovery suggested that instead of anRNA cache the hth-correcting mechanismdepends on ectopic gene conversion(Chaudhury 2005) or on an elusive DNAcache (Ray 2005) Thus all explanationsoffered until now invoke novel geneticphenomena We offer an alternative expla-nation based on established genetic andevolutionaryprinciplesHTHcouldbeameta-bolic enzyme whose impairment causesthe accumulation of toxic and mutageniccompounds that act at random DNA sitesThe observed high reversion rate of hthcould result from selection of rare revertantcells such as pollen and meristem cellsThe frequency of changes at other genomicsites would be overestimated by restrictionenzyme analysis of DNA from chimerictissue Consider the following informationHTH deficiency could result in accumu-

lation of secondary metabolites that are

toxic and mutagenic The HTH gene en-codes a product whose closest character-ized relative is an MBC oxidoreductase thathydrolyzes the aromatic mandelonitrile instone fruits (Zheng and Poulton 1995)(Figure 1A) Arabidopsis has complex met-abolic pathways for the production ofglucosinolates (Wittstock and Halkier2002 Brown et al 2003) some of whichare aromatic and resemble mandelonitrile(Figure 1) and aromatic glucosinolates andtheir derivatives are mutagenic (Musk et al1995 Kassie et al 1999 Kassie andKnasmuller 2000 Canistro et al 2004)The sticky surface properties of the HTHphenotype which suggest alterations ofcuticle cell wall and perhaps membranesmight also be an effect of the toxic mutatorIf an alternative genetic reservoir exists

and it restores mutations to the previousgenotype it should be revised graduallyso that its memory should fade with celldivisions Yet data that addresses thereversion rate are available in a previousarticle by the same group and are inconsis-tent with the above expectation (Lolle et al1998) In complementation tests betweenhth alleles wild-type plants were observedamong the progeny of trans-heterozygotesand were thought to result from intragenicrecombination Thesewere almost certainlyrevertants and not recombinants The hth-10hth-8 trans-heterozygote produced 30wild typesamong1858 individualswhereashth-10hth-4 produced only mutant prog-eny (n1629) (Lolle et al 1998Krolikowskiet al 2003) The same alleles hth-10 andhth-4 were reported to revert in the 2005article and to do so through multiple gen-erations (Lolle et al 2005) Thus the rate ofreversion increased from 1998 to 2005instead of decreasingSelection at multiple stages of develop-

ment could bias the measured reversionrate For example several thousand pollencompete for 20 to 40 eggs Rare HTHpollen could outcompete the preponderanthth pollen (containing the toxic metabolite)

resulting in the enrichment of hthHTHzygotes because the reversion rate wasmuch higher for pollen than for eggs (Figure1B) Our selection hypothesis appears in-consistent with the reported 31 progenyratio from selfed heterozygotes becauseselection in favor of HTH pollen should de-crease the fraction of hthhth progeny butHTH could have a paternal effect where anhthHTH heterozygous anther provides itshth pollen with sufficient HTH enzymeto avoid a crisis An hthhth anther wouldprovide no enzyme Selection favoring re-vertant cells could also act in the shootapical meristem in the flower meristemand in the anther primordia In meristemtissues selection could be influenced bythe defective cellular surface properties ofhth mutants that lead to postgenital organfusion (Lolle et al 1998) Selection couldalso act on seed decreasing germinationof hthhth zygotes in favor of HTHhthindividualsThe precise reversion of hth mutations

without the appearance of secondary mu-tations is consistent with a template-drivenrepair but also with the alternative hypoth-esis of mutagenesis and selection As ex-plained above any significant mutationrate coupled to selection can yield frequentrevertants and the probability of findingsecondary mutations at HTH revertantalleles is proportional to the mutation rateIn fact the highest mutation rate compat-ible with survival is likely to be significantlylower than the rates that would generatefrequent concurrent mutations on the HTHgene We know from TILLING experimentsthe genomic consequences of moderatelyintense mutagenesis in Arabidopsis it pro-duces an average of one mutation for every170 kb (Greene et al 2003) Increasing themutagenesis rate has progressively dele-terious consequences on viability (SHReynolds B Till and L Comai unpublishedresults) and we estimate that a mutationrate 10 times higher (an average of one mu-tation every 17 kb) may not be compatible

The Plant Cell Vol 17 2856ndash2858 November 2005 wwwplantcellorgordf 2005 American Society of Plant Biologists

30

What does it mean for research

Institutionspeers

Educationsystem

Training incorporated

skills

Certified knowledge instruments

33

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Training incorporated

skills

Competitive advantage innovation

Certified knowledge instruments

37

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

41

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Media museumspublic forums

Expertisepopularization

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

0

5

10

15

20

VifLrsquoExpress J du Mardi Le Soir Libre Belgique Tendance LrsquoEcho Derniegravere heure

Percentage of science news in Belgian newspapers

httpwwwbelspobebelspohomepublpub_ostcJournrappULg_frpdf

33

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Training incorporated

skills

Competitive advantage innovation

Certified knowledge instruments

37

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

41

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Media museumspublic forums

Expertisepopularization

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

0

5

10

15

20

VifLrsquoExpress J du Mardi Le Soir Libre Belgique Tendance LrsquoEcho Derniegravere heure

Percentage of science news in Belgian newspapers

httpwwwbelspobebelspohomepublpub_ostcJournrappULg_frpdf

37

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

41

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Media museumspublic forums

Expertisepopularization

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

0

5

10

15

20

VifLrsquoExpress J du Mardi Le Soir Libre Belgique Tendance LrsquoEcho Derniegravere heure

Percentage of science news in Belgian newspapers

httpwwwbelspobebelspohomepublpub_ostcJournrappULg_frpdf

41

What does it mean for research

Institutionspeers

Educationsystem

Economicsystem

Publicauthorities

Media museumspublic forums

Expertisepopularization

Training incorporated

skills

Competitive advantage innovation

Collective goods power prestige

health environment

Certified knowledge instruments

0

5

10

15

20

VifLrsquoExpress J du Mardi Le Soir Libre Belgique Tendance LrsquoEcho Derniegravere heure

Percentage of science news in Belgian newspapers

httpwwwbelspobebelspohomepublpub_ostcJournrappULg_frpdf

0

5

10

15

20

VifLrsquoExpress J du Mardi Le Soir Libre Belgique Tendance LrsquoEcho Derniegravere heure

Percentage of science news in Belgian newspapers

httpwwwbelspobebelspohomepublpub_ostcJournrappULg_frpdf

httpwwwbelspobebelspohomepublpub_ostcJournrappULg_frpdf

Content of these science news

Medicine

Science

Technology

Do you prefer that science information is presented to youhellip

Special Eurobarometer 282 December 2007 p 40

Scientists

Journalists

Other

What could keep you from blogging

bull Internallyndash timendash hot science

48

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

50

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scooped

52

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scoopedndash lack of recognitionndash lack of visibility

54

copycopy alanak

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

What could keep you from blogging

bull Internallyndash timendash hot science

48

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

50

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scooped

52

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scoopedndash lack of recognitionndash lack of visibility

54

copycopy alanak

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

50

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scooped

52

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scoopedndash lack of recognitionndash lack of visibility

54

copycopy alanak

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scooped

52

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scoopedndash lack of recognitionndash lack of visibility

54

copycopy alanak

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

What could keep you from blogging

bull Internallyndash timendash hot sciencendash debating

bull Externallyndash being scoopedndash lack of recognitionndash lack of visibility

54

copycopy alanak

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

copycopy alanak

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

copycopy Aureacutelien Tabard

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

copycopy Manic Street Preacher

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

The landscape of science blogs

bull Communities agregators

58

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

The landscape of science blogs

bull Communities agregatorsbull Rankings

64

The landscape of science blogs

bull Communities agregatorsbull Rankingsbull Diversityndash scientistsndash medicine doctorsndash journalistsndash engineersndash studentsndash teachersndash amateurs 67

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

The landscape of science blogs

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Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68

Nine commandments before you start

bull take your timebull be yourselfbullmatch the form and the contentbull write for everyonebull be transparentbull offer some eye candybull be creativebull foster commentsbull have fun

68