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(P) Biotic Stress: INDUCED DEFENSE AGAINST INSECT HERBIVORES - Coggle…
(P) Biotic Stress: INDUCED DEFENSE AGAINST INSECT HERBIVORES
different types of insect herbivores:
phloem feeders
cell content feeders
chewing insects
the plant response
general wound response
damage + elicitor detection
e.g. fatty acid amides
amplification of the wound response
plt produces
local, systemic and volatile signals :signal_strength:
elicitors from insect herbivores activate the production of
jasmonic acid (JA)
biosynthesis
octadecanoid (18C), in chloroplasts + peroxisomes
beta oxidation
signaling
JA activation by carboxylic acid conjugation with amino acids
binds to
COI1
receptor
ubiquitin E3 ligase complex
binding, poly-ubiquitination and proteasome- mediated degradation of
JAZ transcriptional repressors
de-repression of the MYC2 TF
expression/synthesis of defense proteins
& JAZ genes (feedback!)
JA targets (-> production of):
enzymes in secondary metabolism
proteins that interfere with animal digestion:
α-amylase inhibitors
Leguminosae
lectins
(carbohydrate-binding proteins, often homotetramers)
bind to epithelial cells of the digestive system and block nutrient uptake
protease inhibitors
(a number of insect species have developed resistance)
local and systemic responses
by JA translocation:
through the phloem!
electrical signaling:
injury caused by herbivory activates
glutamate receptor-like (GLR) ion channels in the vascular system
a wave of PM depolarisations
Ca-mediated electrical signal
stimulation of JA production
HIPVs
herbivory-induced plant
volatiles
complex ecological functions
attract enemies & repel pests
some plants use extrafloral nectaries to attract predacious and parasitoid arthropods to protect them
herbivore
species
-specific combination of terpenes, alkaloids, and phenolic compounds
. also production of so-called ‘green-leaf volatiles’ upon herbivore damage
(a mix of
C6
aldehydes, alcohols and esters) to communicate and induce priming
specificity and co-evolution
between plt & herbivore
circadian rhythms
influence plant defense against herbivory
Both herbivory and the JA-mediated defense follow circadian rhythms that peak during the day, maximizing plant protection
Salicylic acid (SA) oppositely peaks during the night for enhanced resistance to pathogenic bacteria in the early morning!
One-third of all plant genes exhibit circadian regulation, including defense genes!
Constitutive versus induced defense
constitutive defense
. often species-specific
. deterring structures and (secondary/specialised) metabolites
. stored active compounds or precursors :moneybag:
induced defense responses
. initiated after damage to the plant
. requires smaller investment, but fast and efficient mechanisms
also involving production of specific proteins
(such as lectins and protease inhibitors) and toxic secondary metabolites