Biology Reference
In-Depth Information
Arabidopsis small GTPase protein AtRac1 has been identifi ed as a central
component in the ABA-mediated stomatal closure (Lemichez et al. 2001 ). ABA
treatment induced inactivation of AtRac GTPases. In contrast, ABA-treatment-
induced AtRac inactivation was not observed in the Arabidopsis ABA-insensitive
mutant abi1-1 , which is impaired in stomatal closure. Expression of a dominant-
positive mutant of AtRac1 blocked the ABA-mediated stomatal closure in wild-
type plants, whereas expression of a dominant-negative AtRac1 mutant
recapitulated the ABA effects in the absence of the hormone. It was also observed
that the dominant-negative form of AtRac1 could restore stomatal closure in the
abi-1 mutant (Lemichez et al. 2001 ). These results demonstrate that a small
monomeric G-protein plays a key role in the stomatal closure immune response
induced by ABA.
3.20
G-Proteins May Participate in Gibberellic Acid
Signaling
Heteromeric G-protein has been reported to play a role in GA signaling system
(Iwasaki et al. 2003 ). GA treatment triggered an increase in expression of
BnG
1 was
more prominently induced by high concentrations of GA (Gao et al. 2010b ). The
expression of BnGA1 encoding a G-protein
β
1 encoding a putative G-protein
β
subunit (G
β
) in Brassica napus . BnG
β
subunit of B . napus was induced by
low gibberellin 3 (GA3) concentrations and higher GA3 concentrations inhibit the
expression of BnGA1 (Gao et al. 2010a ). These results suggest that heterotrimeric
G-proteins may be involved in signaling pathways modulated by GA.
α
3.21
G-Proteins Participate in Brassinosteroid Signaling
G-proteins also take part in activation of brassinosteroid (BR) signaling system. The
α
) has been shown to participate in
BR signaling responses in Arabidopsis and rice (Ullah et al. 2002 ; Wang et al. 2006 ;
Gao et al. 2008 ; Oki et al. 2009 ). The expression of the Brassica napus heterotri-
meric G protein
subunit of plant heterotrimeric G proteins (G
α
subunit ( BnGA1 ) was induced by exogenous application of
brassinosteroid (Gao et al. 2010a ).
Wang et al. ( 2006 ) showed that the rice d1 mutant was less responsive to 24-epi-
brassinolide compared to wild-type plants, suggesting that the rice G
α
α
was involved
in brassinosteroid signaling. Rice G
α
has been shown to affect BR signaling cas-
cade, but G
may not be a signaling molecule in BRI1-mediated perception/trans-
duction (Oki et al. 2009 ). These studies suggest that G-proteins may participate in
BR signaling system.
α
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