Lecture 21: Fungal Pathogens of Plants

• Fruit rot • Stalk rot • Mildew • Wilt • Leaf blight

• Agriculture a. Pathogens can impair crop quality b. Can drastically reduce crop yield (e. g., Irish potato famine)

1. Air-borne fungi: e.g., Blumeria spp. on small grain cereals - causes mildew 2. Soil-borne fungi: e.g., Fusarium and Verticillium - often causes wilt diseases • Economic impact: a. >50% of breeding for disease resistance is against fungal diseases b. reduced biomass and yield c. Cause recurrent seasonal epidemics (e.g., small grain cereals) d. soil-borne fungi tends to cause more chronic infections

• NOT FUNGI • Dispersed via asexual zoospores • Produce oospores (sexual reproduction) • Cellulose cell walls • Diploid • Cause downy: a. mildew diseases b. blights

• Biotrophic a. require living host to grow and reproduce b. Includes obligate parasites that only grow on specific host (e.g., Blumeria) • Necrotrophic a. Kill host cells through action of lytic enzymes and toxins b. colonize and reproduce on dead tissue • Hemi-biotrophic a. grow biotrophically at first then switch to necrotrophy SEE SLIDE FOR DETAILED TABLE OF • attack means • specific features • host range • examples

• Attachment • Penetration • Invasive growth within plant • Suppression/inactivation of host defences

• Invasive growth • Lesions • Sporulation • Attachment • Germination • Hooking • Appressorium • Penetration 5-7 DAYS

Appressoria can generate v. high turgor pressure (6-8 Mpa) - allowing penetration

Plant: Barley Pathogen: Blumeria graminis Plant: Arabidopsis thaliana Pathogen: Erysiphe cruciferarum • Infects: a. barley b. wheat c. rye d. oat • Several ‘forma specialis’ (taxonomic grouping applied to fungi that have adapted to specific host)

1. Specialised structures formed specifically by BIOTROPHIC and HEMITROPHIC fungi a. e.g., graminis 2. Increase SA of contact between fungus and host cell = exchange of: a. nutrients b. and signal molecules

• invaginate the cell following penetration • fungus remains extracellular • two membrane systems from the plant and fungus • separated by extracellular haustoria matrix • Site of delivery for effector molecules and uptake of nutrients

• Tomato leaf mould pathogen: Cladosporium fulvum • Extracellular hyphae do form contacts with leaf mesophyll cells

• Grey mould fungus: Botrytis cinerea • Macerates plant tissue • Broad host range (~200 diff plants) • Prod. cell wall degrading enzymes that destroy plant tissue in advance of colonising hyphae

1. Various effector (Avr) proteins from haustorial biotrophic pathogens a. Proteins DIRECTLY cross the extrahaustorial membrane (1) OR enter cell endomembrane system via vesicles (2) Oomycetes prod. 2 distinct classes of effector: 1. RxLRs - have RxLR motif followed by an E/D-rich region which target the proteins to the host cytoplasm. > 100 RxLR proteins in Phytophthora 2. “Crinklers” (CRNs). Translocated into host nucleus and cause leaf-crinkling and cell-death phenotype

• Rice recognises chitin - a fungal PAMP • Chitin oligosaccharides are bound by chitin elicitor bind protein (CEBiP) initiating defence (=PTI) • Rice blast fungus Magnaporthe oryzae secreted LysM protein 1 (Slp1) binds to chitin and suppresses chitin-induced plant immunity

• it is from Gauemannomyces. graminis f.sp avenae. • degrades antifungal compound avenacin • AVN1 encodes: Avenacinase (beta- glucosyl hydrolase • AVN1 is required by G. graminis var avenae for infection of oats

• Breeding plants began with Sir Rowland Biffen - identified single recessive gene for resistance against “wheat yellow rust” caused by “Puccinia striiformis” • “Green Revolution” of 20th century lead to achievements in wheat, maize, and rice traits: a. increase yield b. improve quality c. Multiline varieties for resistance d. Tolerance to abiotic stresses

• Lr1, 13 a. boom = 1970 b. bust = 1973 • Lr13, 17 a. boom = 1971 b. bust = 1975 • Lr17, 27+31 a. boom = 1973 b. bust = 1977 • Lr13, 26 a. boom = 1981 b. bust = 1984 • Lr23, 26 a. boom = 1982 b. bust = 1985 • Lr14b, 27+31 a. boom = 1992 b. bust = 1994