MALE-STERILITYMALE-STERILITY

Several forms of pollination controlSeveral forms of pollination control

1. Manual emasculation

2. Use of male sterility

3. Use of self-incompatibility

4. Use of male gametocides

5. Use of genetically engineered “pollen killer” genetic system

Male-sterilityMale-sterility

Plant that do not produce viable, functional pollen Plant that do not produce viable, functional pollen grainsgrains

An inability to produce or to release functional An inability to produce or to release functional pollen as a result of failure of formation or pollen as a result of failure of formation or development of functional stamens, microspores or development of functional stamens, microspores or gametesgametes

Phenotypic classes of sterilityPhenotypic classes of sterility

• ““Pollen sterility” in which male sterile individuals Pollen sterility” in which male sterile individuals differ from normal only in the absence or extreme differ from normal only in the absence or extreme scarcity of functional pollen grains (scarcity of functional pollen grains (the most common the most common and the only one that has played a major role in plant and the only one that has played a major role in plant breedingbreeding))

• ““Structural or staminal male sterility” in which male Structural or staminal male sterility” in which male flowers or stamen are malformed and non functional flowers or stamen are malformed and non functional or completely absentor completely absent

• ““Functional male sterility” in which perfectly good Functional male sterility” in which perfectly good and viable pollen is trapped in indehiscent anther and viable pollen is trapped in indehiscent anther and thus prevented from functioningand thus prevented from functioning

Types of Male-sterility

Genetic male sterility

Cytoplasmic male sterility

Environment sensitive genetic male sterility

Chemical induced male sterility

Genetically engineered male sterility

Cytoplasmic male-sterilityCytoplasmic male-sterility

CMS is the result of mutation in the mitochondrial CMS is the result of mutation in the mitochondrial genome (mtDNA), which leads to mitochondrial genome (mtDNA), which leads to mitochondrial dysfunction.dysfunction.

Stamen (anther and filament) and pollen grains Stamen (anther and filament) and pollen grains are affectedare affected

Cytoplasmic male-sterilityCytoplasmic male-sterility

The nuclear genetic control of CMS is predominantly governed by one or more recessive genes, but can be also dominant genes as well as polygenes

The different mtDNA restriction endonuclease digestion patterns are reflections of aberrant intra- or inter molecular DNA recombination events in the mitochondrial genome which have either modified existing genes or related new genes some of which are more or less related to the male sterile phenotypes

Cytoplasmic male-sterilityCytoplasmic male-sterility

Origins:Origins:1. Intergeneric crosses2. Interspecific crosses3. Intraspecific crosses4. Mutagens (EMS, EtBr) 5. antibiotic (streptomycin and Mitomycin) 6. Spontaneus

CMS CharacterizationCMS Characterization

It has been traditionally characterized by the It has been traditionally characterized by the restore genes required to overcome the CMS and to restore genes required to overcome the CMS and to provide male sterile progeny in the male sterile provide male sterile progeny in the male sterile systemsystem

CMS restoration is by nuclear genes, frequently CMS restoration is by nuclear genes, frequently dominant in action, in many cases, few in numberdominant in action, in many cases, few in number

The CMS restore genes temporarily suppress the The CMS restore genes temporarily suppress the expression of the CMS permitting normal or near-expression of the CMS permitting normal or near-normal pollen productionnormal pollen production

TypesTypes

a. Autoplasmica. Autoplasmic CMS has arisen within a species as a result of spontaneous CMS has arisen within a species as a result of spontaneous

mutational changes in the cytoplasm, most likely in the mutational changes in the cytoplasm, most likely in the

mitochondrial genomemitochondrial genome

b. Alloplasmicb. AlloplasmicCMS has arisen from intergeneric, interpecific or occasionallyCMS has arisen from intergeneric, interpecific or occasionally

intraspecific crosses and where the male sterility can be intraspecific crosses and where the male sterility can be

interpreted as being due to incompatibility or poor co-interpreted as being due to incompatibility or poor co-operationoperation

between nuclear genome of one species and the organellar between nuclear genome of one species and the organellar

genome anothergenome another

CMS can be a result of interspecific protoplast fusionCMS can be a result of interspecific protoplast fusion

CMS mechanism of action

Abnormal behavior of the tapetum in the anther

Genetic determinant of CMS reside in mitochondria

Nuclear gene control the expression of CMS

CMS LimitationsCMS Limitations

Pleiotropic negative effect of the CMS on agronomic Pleiotropic negative effect of the CMS on agronomic quality performance of plants in the CMS cytoplasmquality performance of plants in the CMS cytoplasm

Enhanced disease susceptibilityEnhanced disease susceptibility

Complex and environmentally unstable maintenance of Complex and environmentally unstable maintenance of male sterility and/or male fertility restorationmale sterility and/or male fertility restoration

Inability to produce commercial quantities of hybrid Inability to produce commercial quantities of hybrid

seed economically because of poor floral characteristic seed economically because of poor floral characteristic of cross pollinationof cross pollination

CMS UtilizationCMS Utilization

It provides a possible mechanism of pollination It provides a possible mechanism of pollination control in plants to permit the easy production of control in plants to permit the easy production of commercial quantities of hybrid seedscommercial quantities of hybrid seeds

It consists of a male sterile line (the A-line), an It consists of a male sterile line (the A-line), an isogenic maintainer line (The B line), and if isogenic maintainer line (The B line), and if necessary also restore line (the R-line)necessary also restore line (the R-line)

A lines are developed by back-crossing selected A lines are developed by back-crossing selected B-lines to a CMS A-line for 4 – 6 times to generate B-lines to a CMS A-line for 4 – 6 times to generate a new A-line, B and R-lines are developed by a new A-line, B and R-lines are developed by similar back cross procedures using a CMS R-line similar back cross procedures using a CMS R-line as female in the original cross and a new line as as female in the original cross and a new line as the recurrent parent in 4 – 6 backcrossesthe recurrent parent in 4 – 6 backcrosses

CMS UtilizationCMS Utilization

Selfing the last backcross generation two Selfing the last backcross generation two successive times and selection of pure successive times and selection of pure breeding male fertility restore line is required breeding male fertility restore line is required to complete the development of the new R-to complete the development of the new R-lines developed in the CMS lines developed in the CMS

Current commercial hybrid seed production Current commercial hybrid seed production relies entirely on the block method relies entirely on the block method (alternating strips of female and male (alternating strips of female and male genotypes genotypes

Fertility restoration in maizeFertility restoration in maize

Simple hybrid with cms and restorationSimple hybrid with cms and restoration

Maintainer line (B-line)N, rfrf

rrS

Large amountsof CMS line

xCMS line (A-line)CMS, rfrf

rrF

rrS

Fx RRMale line (C-line)N and RfRf

Rr

S

Fertile F1 hybridCMS, Rfrf

Originated through spontaneous mutation or Originated through spontaneous mutation or mutation by ionizing radiation and chemical mutation by ionizing radiation and chemical mutagens such as ethyl methane sulphonate (EMS) mutagens such as ethyl methane sulphonate (EMS) and ethyl imine (EI) or by genetic engineering, and ethyl imine (EI) or by genetic engineering, protoplast fusionprotoplast fusion

can probably be found in all diploid speciescan probably be found in all diploid species

Usually controlled by mutations in genes in the Usually controlled by mutations in genes in the single recessive genes affect stamen and pollen single recessive genes affect stamen and pollen development, but it can be regulated also by development, but it can be regulated also by dominant genesdominant genes

Nuclear male sterility

Variable (complete absence of male Variable (complete absence of male reproductive organs to the formation of reproductive organs to the formation of normal stamen with viable pollen that fail to normal stamen with viable pollen that fail to dehisce)dehisce)

It is not distinguishable from parent fertile It is not distinguishable from parent fertile plants with the exception of flower structureplants with the exception of flower structure

Male sterile flowers are commonly smaller Male sterile flowers are commonly smaller in size in comparison to the fertilein size in comparison to the fertile

The size of stamens is generally reducedThe size of stamens is generally reduced

Morphology

Temperature (TGMS)Temperature (TGMS)Changing the optimal temperature can induce Changing the optimal temperature can induce

sterility (23°C)sterility (23°C) Photoperiod (PGMS)Photoperiod (PGMS)

It has a strong influence (Photoperiod sensitive)It has a strong influence (Photoperiod sensitive)

Changing the growth habit can stimulate the Changing the growth habit can stimulate the sterility sterility

(23°C - 29°C)(23°C - 29°C)

Determining factor

Breakdown in microsporogenesis can occur Breakdown in microsporogenesis can occur at a number of pre-or postmeiotic stagesat a number of pre-or postmeiotic stages

The abnormalities can involve aberration The abnormalities can involve aberration during the process of meiosis, in the during the process of meiosis, in the formation of tetrads, during the release of formation of tetrads, during the release of tetrad (the dissolution of callose), at the tetrad (the dissolution of callose), at the vacuolate microspore stage or at mature or vacuolate microspore stage or at mature or near-mature pollen stagenear-mature pollen stage

Cytological Changes

Male sterile plants of monoecious or Male sterile plants of monoecious or hermaprodite crops are potentially useful in hermaprodite crops are potentially useful in hybrid program because they eliminate the hybrid program because they eliminate the

labor intensive process of flower emasculationlabor intensive process of flower emasculation

Use of genic male sterility in hybrid programs

Hybrid seed production with GMS and Hybrid seed production with GMS and restorationrestoration

Male sterile lineMale sterile line X X Male Male fertile linefertile line

msmsmsms MsMs MsMs

Male sterile lineMale sterile line X X Maintainer lineMaintainer line

msmsmsms Msms Msms

Seed for harvested in bulk from male sterile line

Maintenance plot Maintenance plot Hybrid seed production Hybrid seed production plotplot Plants with

Msms and msms genotypes

Female rows male rows Female rows

Msms & msms Msms & msms

Harvest seed only from sterile plants

Remove fertile plants from rows before anthesis, harvest seed from sterile plants

Cytoplasmic-genetic male sterilityCytoplasmic-genetic male sterility

• A case of cytoplasmic male sterility where A case of cytoplasmic male sterility where a nuclear gene for restoring fertility in the a nuclear gene for restoring fertility in the male sterile line is known.male sterile line is known.

• The fertility restorer gene R is dominant. The fertility restorer gene R is dominant.

Various Genotypes and PhenotypesVarious Genotypes and Phenotypes

rrS

RRS

rrF

Cytoplasm sterileNuclear gene non restorer

RrS

Cytoplasm fertileNuclear gene non restorer

Cytoplasm sterile (Male fertile)Nuclear gene restorer in homozygous RR or heterozygous Rr stateThe effect of sterile cytoplasm is negated by the restorer gene

CHEMICAL INDUCED MALE-CHEMICAL INDUCED MALE-STERILE STERILE

Biochemical means of Biochemical means of producing male sterile plantsproducing male sterile plants

Feminizing hormonesFeminizing hormones Inhibitors of anther or pollen Inhibitors of anther or pollen

developmentdevelopmentInhibitors of pollen fertilityInhibitors of pollen fertility

Chemical hybridizing agent (CHA)Chemical hybridizing agent (CHA)

Could be used in the large scale Could be used in the large scale commercial production of hybrid seedcommercial production of hybrid seed

Are applied to plant only at certain Are applied to plant only at certain critical stage of male gametophyte critical stage of male gametophyte developmentdevelopment

The logic of chemical hybridizationThe logic of chemical hybridization

High degree of efficacy and developmental selectivityHigh degree of efficacy and developmental selectivity Persistence during the development of flower or spikesPersistence during the development of flower or spikes Low costLow cost Acceptable levels of toxicity to people and the environmentAcceptable levels of toxicity to people and the environment Low general phytotoxicityLow general phytotoxicity Agronomic performance of hybrid seed produced is not Agronomic performance of hybrid seed produced is not

inferior to equivalent crosses produced by genetic methodsinferior to equivalent crosses produced by genetic methods

CHAs and pollen developmentCHAs and pollen development

There are at least 4 classes of chemical agentsThere are at least 4 classes of chemical agents::

aa. Plant growth regulators and substances that . Plant growth regulators and substances that

disrupt floral disrupt floral developmentdevelopment

b. Metabolic inhibitorsb. Metabolic inhibitors

c. inhibitors of microspore developmentc. inhibitors of microspore development

d. inhibitors of pollen fertilityd. inhibitors of pollen fertility

Plant growth regulators and substances that Plant growth regulators and substances that disrupt floral developmentdisrupt floral development

Plant hormones/hormones antagonistsPlant hormones/hormones antagonistsa. auxins and auxin antagonists (NAA, IBA, 2,4-D, a. auxins and auxin antagonists (NAA, IBA, 2,4-D, TIBA, MH)TIBA, MH)

b. Gibberellins and antagonist (GA3, GA4+7, CCC: 2-b. Gibberellins and antagonist (GA3, GA4+7, CCC: 2-chloroethyl-trimethyl ammonium chloride)chloroethyl-trimethyl ammonium chloride)

c. Abscisic acidc. Abscisic acid

Other substancesOther substancesa. LY195259a. LY195259

b. TD1123b. TD1123

Metabolic InhibitorsMetabolic Inhibitors

There are halogenated aliphatic acids (alpha, beta-There are halogenated aliphatic acids (alpha, beta-dichloroisobutyrate and 2,2-dichloropropionate salts) dichloroisobutyrate and 2,2-dichloropropionate salts) and arsenicals (methanearsonate salts)and arsenicals (methanearsonate salts)

They affect mitochondrial protein by reducing the They affect mitochondrial protein by reducing the efficiency of normal metabolic processesefficiency of normal metabolic processes

Inhibitors of microspore Inhibitors of microspore developmentdevelopmentCopper chelatorsCopper chelators

EthyleneEthylene

FenridazonFenridazon

Phenylcinnoline carboxylates (SC-1058, SC-Phenylcinnoline carboxylates (SC-1058, SC-1271 and SC-2053)1271 and SC-2053)

Inhibitors of pollen fertilityInhibitors of pollen fertility

Azetidine-3-carboxylate (A3C, CHA™)Azetidine-3-carboxylate (A3C, CHA™)