Lecture 21: Fungal Pathogens of Plants Flashcards
What are different types of plant disease?
- Fruit rot
- Stalk rot
- Mildew
- Wilt
- Leaf blight
Why study plant microbe interactions?
The importance of plant disease
- Agriculture
a. Pathogens can impair crop quality
b. Can drastically reduce crop yield
(e. g., Irish potato famine)
What are the different forms of fungal infections? What is there economic impact?
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
What is Oomycetes?
- NOT FUNGI
- Dispersed via asexual zoospores
- Produce oospores (sexual
reproduction) - Cellulose cell walls
- Diploid
- Cause downy:
a. mildew diseases
b. blights
What are the three strategies used by fungi to infect plants?
- 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
What are the 4 key stages of fungal pathogenesis?
- Attachment
- Penetration
- Invasive growth within plant
- Suppression/inactivation of host
defences
What is the infection cycle of rice blast fungus? How long does it take?
- Invasive growth
- Lesions
- Sporulation
- Attachment
- Germination
- Hooking
- Appressorium
- Penetration
5-7 DAYS
How does a fungus penetrate the cuticle and cell wall?
Appressoria can generate v. high turgor pressure (6-8 Mpa) - allowing penetration
What is an example of biotrophic pathogens?
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)
What are fungal haustoria’s?
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 moleculesWhat is the structure of haustoria?
- 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
What is an example of a biotroph that doesn’t produce haustoria
- Tomato leaf mould pathogen:
Cladosporium fulvum - Extracellular hyphae do form contacts
with leaf mesophyll cells
What is an example of a necrotoph
- 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
What determines virulence?
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
How does the “Magnaporthe oryzae” effector Slp1 suppress chitin-triggered defence response in rice?
- 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
