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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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