fungal plant pathogens Flashcards
what type of feeding organism are fungi?
saprophytes that feed via osmotrophy
This is because chitin walls prevent engulfing food.
how do fungi grow?
Fungal hyphae, cylindrical cells enclosed in chitinous cell wall, operate as a single unit, allowing for indefinite apical growth.
Some can produce single celled yeast and reproduce via budding.
Some can switch between both methods
pathogenic fungi are responsible for ___ crop diseases
70-80%
how to pathogenic fungi attach to plants?
fungal attachment involves spores being dispersed by wind, water, insects and actively/passively attaching to plant surfaces.
the fungi secrete mucilage and fungi has a hydrophobic proteinous structure made of hydrophobins on its surface
tell me about pathogenic fungi germination
the spore germinates, producing a germ tube. The germ tube tip differentiates into a swelled structure called a appressorium. The appressorium tightly attaches to host surface, producing a penetration peg.
The appressorium asserts up to 8.0mpa pressure onto the penetration peg, along with enzymatic degradation of host cuticle and cell wall
Penetration can also be through stomata
what are the two types of host dependency?
Obligate pathogen - depend entirely on host and mirror their life cycle
Facultative pathogen - can complete lifecycle away from host
How are pathogenic fungi classified depending on how they get nutrients?
biotroph - feed on living tissue without killing
necrotroph - kill host and feed
hemibiotroph - bit of both
How do biotrophic pathogenic fungi feed?
they must keep the plant alive!
penetrate cell wall and produce infection structure called a haustoria
- the haustoria doesn’t disrupt cell membrane, and instead invaginates
how do necrotrophic pathogenic fungi feed?
The initial reaction is with living tissue, however the fungi needs the tissue to be dead, so it subverts plant defences to generate necrotic tissue. here the fungi is protected
how do hemi-biotrophic pathogenic fungi feed?
they carry out biotrophic nutrition, producing a haustoria, however eventually kill tissue creating necrotic tissue
Tell me about the plant pathogen arms race (plant side)
The R-protein in plants can detect the AVR-protein in pathogens, and will initialise hypersensitive response. Also, plant receptors can recognise chitin and glucans and produce chitinase and glucanase to compromise cell wall. NADPH oxidase can produce superoxide, and superoxide dismutase can produce H2O2, aswell as altering pH
Tell me about the plant pathogenic arms race (pathogen side)
In response to plant receptors, pathogen can secrete effectors that disturb recognition in immune sensors, effectors that subvert plant defence response, effectors that hijack plant metabolism.
In response to chitinase and glucanase, pathogen can alter cell wall components and produce proteases to compromise said proteins
