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(P) Biotic Stress: INDUCED DEFENSE AGAINST PATHOGENS - Coggle Diagram
(P) Biotic Stress: INDUCED DEFENSE AGAINST PATHOGENS
Pathogens use different infection strategies:
invasion
proliferation
production of effectors that facilitate invasion and proliferation
enzymes
toxins
growth regulators
TAL (transcription activator-like) effectors
target the nucleus and activate gene expression (e.g. sugar transporters)
hormone signaling, production of antimicrobial compounds
plant defense against microbial attack is mediated by 3 plant hormones:
ethylene
effective against cell death-provoking necrotrophic pathogens (and herbivores)
salicylic acid
typically effective against biotrophic pathogens
jasmonic acid
hypersensitive response
local programmed cell death (PCD), preventing spreading of the pathogen
oxidative burst (ROS) and Ca2+ accumulation:
Ca2+ is both needed for and a negative regulator of SA biosynthesis
Pathogen recognition by the plant:
PAMPs
Gram +
cc wall
Gram -
Lipopolysaccharides, LPS (endotoxins)
Flagellin
fungi
chitin
ergosterol
PRRs
2 major types:
RLK, receptor-like kinases
key role for MAPK signaling
RLP, receptor-like proteins
Phytoalexin production
induction (gene expression) + accumulation at the site of infection
specialized pathogens develop strategies to by-pass resistance
Effector-Triggered Susceptibility or
ETS
However: plants have developed the ability to recognize specific effectors
resulting in an (often fiercer) response and effector-triggered immunity,
ETI
match of specific effector gene (protein) and resistance (R) gene (protein) =
“gene-for-gene resistance” principle
receptors
Resistance (R) proteins:
2 major classes:
NB-LRR class
eLRR class
response to viral infection
silencing by RNAi (RNA interference)
The growth/defense trade-off
cost of a reduction in growth and reproduction, because of
metabolic expenditure
antagonistic
crosstalk among stress/defense and growth hormones