G-Proteins as Molecular Switches in Signal Transduction - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 187

resistance to Tobacco mosaic virus infection by inducing salicylic acid (Sano
et al. 1994 ). Collectively these studies suggest that G-proteins play an important
role in SA biosynthesis and signal transduction in plant innate immune responses.

3.17 G-Proteins Trigger Ethylene Signaling Pathway

G-protein may trigger ethylene-dependent signaling pathway. G-proteins have
been recognized as crucial signal transducers in ethylene-mediated signaling
(Steffens and Sauter 2010 ). The rice small G-protein OsRac1 induced methionine
synthase and S-adenosyl-methionine synthase in rice cells (Fujiwara et al. 2006 ).
Methionine synthase is involved in conversion of homocysteine to methionine and
S-adenosyl-methionine synthase catalyses the formation of S-adenosyl-methionine.
S-adenosylmethionine is a precursor of ethylene and it is converted into 1-amino-
cyclopropane-1-carboxylic acid (ACC) by the action of ACC synthase. ACC is
oxidized by ACC oxidase resulting in the formation of ethylene (Fig. 3.9 ; Wang
et al. 2002 ; Vidhyasekaran 2007 ).

Homoserine

Small G-protein

Activation

Methionine
synthase

Methionine

S-adenosyl-
methionine
synthase

Small G-protein

Activation

S-adenosyl - methionine

ACC synthase

1- Aminocyclopropane -1-
carboxylic acid (ACC)

ACC oxidase

Fig. 3.9 G-protein - induced
ethylene biosynthesis

Ethylene