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

* *

TMV plaques in scion leaves

Vernooij, B. et al. 1994, Plant Cell 6: 959-965

X/N N/X

X/XN/N

Crunchers vs suckers

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.

Pseudomonas syringae alters the immune balance of the plant

RR or Rr rr

Avr1 No disease Disease

avr1 Disease Disease

The gene-for-gene resistance model

RR or Rr rr

Avr1 No disease Disease

avr1 Disease Disease

The gene-for-gene resistance model

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 mildew

Erysiphe 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

1 2

0

5

10

15

20

25

30

Wt

48M3

136N4

114N4

Phenotype Quantification%

of g

erm

inat

ed s

pore

s

****

**

**

**

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.