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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
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Basic defenses of a plant
Living in the apoplast
Hypersensitive responses kill small parts of the leaf
res2.agr.gc.ca/ecorc/ corn-mais/images/fig-22.jpg
http://ppathw3.cals.cornell.edu/PhotoLab/Stills/Tobacco/Tobacco.jpg
Hypersensitive response
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Systemic acquired immunity
Involves salicylate but this is not
the factor acting through the plant
wt No Salicylate
No SAR in scion
Vernooij, B. et al. 1994, Plant Cell 6: 959-965
TMV plaques in scion leaves
X/N N/X
X/X N/N
Vernooij, B. et al. 1994, Plant Cell 6: 959-965
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
No JA Constitutive JA
Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):19237-42.
Crunchers vs suckers
Pseudomonas syringae alters
the immune balance of the plant
The gene-for-gene resistance model
Host Genes
RR or Rr rr
Microbe Genes
Avr1 No disease DISEASE
avr1 Disease Disease
Similarity between R genes and Toll
Staskawicz B.J. et al. Science, 2001 5525: 2285-9
Bacteria secrete proteins into the plant cell
Cytoplasm using a type III secretion system
Host cytoplasm
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Bacterial cell
Crunchers vs suckers
Mi-1 is an R gene giving resistance to
nematode and aphid infection
Wild type: Carrying Mi-1
Aphid infested
Vos, P. et al. 1998 Nature Biotechnology 16: 1365-69
Fungi must break through the
surface of the leaf
http://www.nysaes.cornell.edu/pp/faculty/hoch/images/black_
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Arabidopsis Barley
powdery mildew powdery mildew (Bgh)
Erysiphe cichoracearum Blumeria graminis f.sp hordei
Host infection Nonhost infection Host infection
on Arabidopsis on Arabidopsis on Barley
From : Monica Stein, Somerville lab, Stanford
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Structure of the penetration peg
Erysiphe cichoracearum on Arabidopsis Blumeria graminis f.sp. hordei on Arabidopsis
Spore Appressorium Appressorium
A) germination and attempted
penetration
Host: Nonhost:
95% 90% Spore
Hypha
haustorium B) penetration and haustorial haustorium
development
Host: Nonhost:
90% 4%
hyphae C) Hyphal elongation hyphae
Host: Nonhost:
90% 2%
cell death
D) Conidiation
Host: Nonhost:
conidia
90% 0%
host Cytological Characterization
(Zimmerli,L; Stein,M; Lipka,V; Schulze-Lefert,P; Somerville,SC,
Plant Journal (2004))
• callose deposition in response
to pathogen attack was
dramatically different between
Papillae host and nonhost inoculation.
H
P
nonhost • Nonhost haustoria were
rapidly encased in callose
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
Phenotype Quantification
30
**
25
% of germinated spores
**
20 **
Wt
15 pen1
48M3
pen2
136N4
10 ** pen3
114N4
* * **P<.0001
5
*P<.01
0
1 2
Penetration Elongated Hyphae
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.
