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Phosphatidylinositol
Phosphatidylinositol
-4,5-bisphosphate
Activation
Activation
PAMP signal
G-protein
Phospholipase C
Diacylglycerol
Activation
Phospholipse D
Phosphatidyl choline
Phosphatidic acid
NADPH oxidase
ROS
Fig. 3.6 Generation of ROS by phosphatidic acid through the action of G-protein-activated
phospholipases
NADPH oxidase (Sang et al. 2001 ). PA has been shown to induce ROS in tomato
cells. Inhibition of the PLC diminished elicitor-induced ROS production (Laxalt
et al. 2007 ). These results suggest that PA is generated through the action of
G-proteins-activated phospholipases and the generated PA activates NADPH oxi-
dase involved in generation of ROS (Fig. 3.6 ).
3.12.5
Small G-Proteins May Trigger Accumulation of ROS
by Suppressing the Action of ROS Scavengers
Small G-proteins may act as a suppressor of ROS scavenging, resulting in accumu-
lation of ROS (Wong et al. 2004 ). Metallothioneins are small, ubiquitous Cys-rich
proteins involved in ROS scavenging. The expression of the metallothionein gene
( OsMT2b ) was synergistically down-regulated by OsRac1 and PAMPs from
Magnaporthe oryzae , the rice blast pathogen. OsMT2b -overexpressing cells showed
reduced PAMP-induced H 2 O 2 production. In contrast, OsMT2b -RNAi-silenced
transgenic cells showed signifi cantly higher PAMP-induced OsRac1-dependent
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