Types of plant pathogens

Necrotrophic pathogen

Biotrophic pathogen

Hemibiotrophic

Plants cannot do many things

QuickTime™ and aAnimation decompressor

are needed to see this picture.

QuickTime™ and aAnimation decompressor

are needed to see this picture.

QuickTime™ and aAnimation decompressor

are needed to see this picture.

QuickTime™ and aAnimation decompressor

are needed to see this picture.

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

QuickTime™ and aAnimation decompressor

are needed to see this picture.

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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

QuickTime™ and aAnimation decompressor

are needed to see this picture.

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aCinepak decompressor

are needed to see this picture.

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

QuickTime™ and aAnimation decompressor

are needed to see this picture.

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.