Mitogen-Activated Protein Kinase Cascades in Plant Innate Immunity - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 340

Fig. 7.2 Role of a MAPKKK
(EDR1) in modulation of
SA-JA-ET signaling system
in rice plant immune
responses (Adapted from
Shen et al. 2011 )

OsEDR1

ACC synthase

ACC biosynthesis

Ethylene

OsEDR1 is a sequence ortholog of Arabidopsis EDR1. It has been shown that
OsEDR1 negatively regulates plant defense responses via the activation of
ethylene biosynthesis (Shen et al. 2011 ). OsEDR1-suppressing knockout (KO)
rice plants showed enhanced resistance against the bacterial blight pathogen
Xanthomonas oryzae pv. oryzae . This resistance was associated with increased
accumulation of SA and JA, induced expression of SA- and JA-related defense
genes and suppressed accumulation of 1-aminocyclopropane-carboxylic acid
(ACC), the precursor of ethylene, and expression of ethylene-related genes.
Knockout of OsEDR1suppressed the ACC synthase (ACS) gene family, which
encodes the enzymes of ethylene biosynthesis by catalyzing the formation of ACC.
The enhanced disease resistance of the OsEDR1-knockout plants was comple-
mented by ACC treatment. ACC treatment decreased SA and JA biosynthesis in
OsEDR1-knockout plants. In contrast, aminoethoxyvinylglycine, the inhibitor of
ethylene biosynthesis promoted expression of SA and JA synthesis-related genes
in OsEDR1-knockout plants (Shen et al. 2011 ). These studies show that OsEDR1
transcriptionally promotes the synthesis of ethylene that, in turn, suppresses SA- and
JA-associated defense signaling (Fig. 7.2 ).