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
Microbe Genes
Host Genes
RR or Rr
rr
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:
Aphid infested
Carrying Mi-1
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
powdery mildew
Barley
powdery mildew (Bgh)
Erysiphe cichoracearum
Blumeria graminis f.sp hordei
Host infection
on Arabidopsis
Nonhost infection
on Arabidopsis
Host infection
on Barley
From : Monica Stein, Somerville lab, Stanford
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Structure of the penetration peg
Erysiphe cichoracearum on Arabidopsis
Spore
Appressorium
Hypha
haustorium
Blumeria graminis f.sp. hordei on Arabidopsis
A) germination and attempted
penetration
Nonhost:
90%
Host:
95%
Spore
B) penetration and haustorial
development
Host:
90%
hyphae
C) Hyphal elongation
hyphae
Nonhost:
2%
cell death
D) Conidiation
Host:
90%
haustorium
Nonhost:
4%
Host:
90%
conidia
Appressorium
Nonhost:
0%
Cytological Characterization
host
(Zimmerli,L; Stein,M; Lipka,V; Schulze-Lefert,P; Somerville,SC,
Plant Journal (2004))
Papillae
• callose deposition in response
to pathogen attack was
dramatically different between
host and nonhost inoculation.
H
P
• Nonhost haustoria were
rapidly encased in callose
From : Monica Stein, Somerville lab, Stanford
nonhost
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
% of germinated spores
30
25
**
**
**
20
15
**
10
*
5
*
0
1
Penetration
2
Elongated Hyphae
From : Monica Stein, Somerville lab, Stanford
Wt
pen1
48M3
pen2
136N4
pen3
114N4
**P<.0001
*P<.01
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.