G-Proteins as Molecular Switches in Signal Transduction - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 169

Fig. 3.3 Heterotrimeric
G-protein acting upstream
of small G-protein in immune
signaling system in rice cells
(Adapted from Suharsono
et al. 2002 )

PAMP

Receptor

Heterotrimeric
G-protein G α subunit

Small G-protein osRac1

PR gene expression

α

These results suggest the involvement of both the heterotrimeric G-protein G

subunit and small G-protein OsRac1 in defense signaling and the heterotrimeric
G-protein G

α

acts upstream of small G protein OsRac1 in rice cells.

3.5 Different G-Protein Subunits in Heterotrimeric

G-Proteins Play Distinct Roles in Plant Innate Immunity

α β γ

Heterotrimeric G-proteins contain subunits and these subunits may

behave differently in inducing defense responses. For example, the

, , and

β γ

subunits
were involved in triggering immune responses against necrotrophic fungal patho-
gens, while the

and

α

subunit conferred susceptibility against these pathogens in
Arabidopsis . The Arabidopsis

α

subunit gpa1 mutant exhibited enhanced resistance
to several necrotrophic fungal pathogens, including Plectosphaerella cucumerina ,