Types of plant pathogens Necrotrophic pathogen Biotrophic pathogen Hemibiotrophic

Plants cannot do many things

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 Hypersensitive responses kill small parts of the leaf

Hypersensitive response

Systemic acquired immunity

Involves salicylate but this is not the factor acting through the plant Vernooij, B. et al. 1994, Plant Cell 6: wt No Salicylate No SAR in scion

TMV plaques in scion leaves Vernooij, B. et al. 1994, Plant Cell 6: X/N N/X X/X N/N

JA induction by insects and necrotrophs 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 Dec 27;102(52): No JAConstitutive JA

Crunchers vs suckers

Pseudomonas syringae alters the immune balance of the plant

RR or Rrrr Avr1No diseaseDISEASE avr1Disease The gene-for-gene resistance model Host Genes Microbe Genes

Similarity between R genes and Toll Staskawicz B.J. et al. Science, :

Bacterial cell Host cytoplasm Bacteria secrete proteins into the plant cell Cytoplasm 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 Nature Biotechnology 16: Wild type: Aphid infested Carrying Mi-1

Fungi must break through the surface of the leaf rot6.gif

Barley powdery mildew (Bgh) Blumeria graminis f.sp hordei Nonhost infection on Arabidopsis Arabidopsis powdery mildew Erysiphe cichoracearum Host infection on Arabidopsis Host infection on Barley From : Monica Stein, Somerville lab, Stanford

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 hyphae conidia cell death Erysiphe cichoracearum on ArabidopsisBlumeria 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 WTpen1 From : Monica Stein, Somerville lab, Stanford

pen3 plants allow more hyphal growth than other pen mutants WTpen3 From : Monica Stein, Somerville lab, Stanford

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 :