G-Proteins as Molecular Switches in Signal Transduction - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 183

Fig. 3.7 Heterotrimeric
G protein-mediated nitric
oxide (NO) production
in Arabidopsis (Adapted
from Li et al. 2009 )

Heterotrimeric G-protein Gα subunit

Activation

NADPH oxidase

H 2 O 2

Activation

NO production

H 2 O 2 -induced NO production depended mainly on NITRIC OXIDE
ASSOCIATED 1 (NOA1) (also called NITRIC OXIDE SYNTHASE1 [NOS1])
(Li et al. 2009 ). However Bright et al. ( 2006 ) reported that it is NITRATE
REDUCTASE (NR), not NOA, that is responsible for NO generation in Arabidopsis
in response to H 2 O 2 .

3.14 Close Relationship Between G-Proteins and MAPKs

in Signal Transduction

Both hetrotrimeric and small monomer G-proteins may be required for defense
signaling (Zhao et al. 2010 ; Zhang et al. 2011 , 2012 ; Kiirika et al. 2012 ). Mitogen-
activated protein kinases (MAPKs) are involved in defense signaling system (Liu
et al. 2011 ; Mao et al. 2011 ). A close relationship between MAPKs and G-proteins
in the transduction of external signals into intracellular responses has been reported
(Lieberherr et al. 2005 ).
To study the importance of these two types of G-proteins in defense signaling,
transgenic rice cell lines in which the small G-protein OsRac1 gene was specifi -
cally silenced by RNA interference and loss-of-function mutant rice cells
containing heterotrimeric G

mutation were obtained (Lieberherr et al. 2005 ).
There was a strong reduction of OsRac1 protein level in the transgenic plants and
these transgenic plants also showed strong reduction in MAPK protein level. In
the OsRac1 -RNAi line, the MAPK activity was not induced by an elicitor,

α