Types of plant pathogens
Necrotrophic pathogen
Biotrophic pathogen
Hemibiotrophic
Plants cannot do many things
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Plants have disposable body parts; we don’t
Basic defenses of a plant
Living in the apoplast
res2.agr.gc.ca/ecorc/ corn-mais/images/fig-22.jpg
http://ppathw3.cals.cornell.edu/PhotoLab/Stills/Tobacco/Tobacco.jpg
Hypersensitive responses kill small parts of the leaf
Hypersensitive response
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Systemic acquired immunity
Involves salicylate but this is not the
factor acting through the plant
Vernooij, B. et al. 1994, Plant Cell 6: 959-965
wt No Salicylate
No SAR in scion
TMV plaques in scion leaves
Vernooij, B. et al. 1994, Plant Cell 6: 959-965
X/N N/X
X/X N/N
JA induction by insects and necrotrophs
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Biochemistry and Molecular Biology of Plants, Buchanan et al. ed, 2000
Arginine and threonine depletion in the gut
Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):19237-42.
No JA Constitutive JA
Crunchers vs suckers
Pseudomonas syringae alters the immune balance of the plant
RR or Rr rr
Avr1No
diseaseDISEASE
avr1 Disease Disease
The gene-for-gene resistance model
Host Genes
Microbe Genes
Similarity between R genes and Toll
Staskawicz B.J. et al. Science, 2001 5525: 2285-9
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Bacterial cell
Host cytoplasm
Bacteria secrete proteins into the plant cellCytoplasm using a type III secretion system
Crunchers vs suckers
Mi-1 is an R gene giving resistance to nematode and aphid infection
Vos, P. et al. 1998 Nature Biotechnology 16: 1365-69
Wild type:Aphid infested
Carrying Mi-1
Fungi must break through the surface of
the leaf http://www.nysaes.cornell.edu/pp/faculty/hoch/images/black_rot6.gif
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Barley powdery mildew (Bgh)
Blumeria graminis f.sp hordei
Nonhost infection on Arabidopsis
Arabidopsispowdery mildewErysiphe cichoracearum
Host infectionon Arabidopsis
Host infectionon Barley
From : Monica Stein, Somerville lab, Stanford
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Structure of the penetration peg
A) germination and attempted penetration
Spore Appressorium
Hypha
Host:95%
Host:90%
Host:90%
Spore
Appressorium
Nonhost:90%
Nonhost:2%
Nonhost:4%
C) Hyphal elongation
B) penetration and haustorial development
D) Conidiation
Host:90%
Nonhost:0%
haustorium haustorium
hyphae hyphae
conidia
cell death
Erysiphe cichoracearum on Arabidopsis Blumeria graminis f.sp. hordei on Arabidopsis
Cytological Characterization
(Zimmerli,L; Stein,M; Lipka,V; Schulze-Lefert,P; Somerville,SC, Plant Journal (2004))
host
nonhost • Nonhost haustoria were rapidly encased in callose
• callose deposition in response to pathogen attack was dramatically different between host and nonhost inoculation.
P
H
Papillae
From : Monica Stein, Somerville lab, Stanford
Callose is deposited at infection sites
pen mutants
WT pen1
From : Monica Stein, Somerville lab, Stanford
pen3 plants allow more hyphal growth than other pen mutants
WT pen3
From : Monica Stein, Somerville lab, Stanford
0
5
10
15
20
25
30
1 2
Wt
48M3
136N4
114N4
Phenotype Quantification% of germinated spores
****
**
**
**
Elongated HyphaePenetration
pen1
pen2
pen3
P<.0001 P<.01***
From : Monica Stein, Somerville lab, Stanford
The story is complicated: Mutation of the callose
synthase increases resistance to a fungal pathogen
Nishimura, M.T. et al. Science 2003 301: 969-72.