G-Proteins as Molecular Switches in Signal Transduction - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 191

regulated by G -dependent pathways. These channels are activated by ABA and

this activation is lost in gpa1 mutant lines (Zhang et al. 2011 ). The results suggest
that ABA activation of these channels is dependent on G-proteins.

α

3.19.4 ABA Increases Expression of Genes Encoding

Heterotrimeric G-Proteins

ABA treatment triggered an increase in expression of BnG β 1 encoding a putative

G-protein 1 was induced

by low ABA concentrations, but high ABA concentrations inhibited the expression,
suggesting that there might be an ABA-mediated feedback expression of
BnG

β subunit (G β ) in Brassica napus . The expression of BnG β

1 expression (Gao et al. 2010b ). In contrast, the expression of BnGA1 encod-
ing G

β

G-protein subunit in B . napus was signifi cantly induced by the high
concentrations of ABA (Gao et al. 2010a ). These results suggest that the hetero-
meric G-protein may participate in ABA signaling system.

α

3.19.5 G-Protein May Play a Role in ABA Signaling Between

ABA Reception and ROS Production

The participation of G-proteins in ABA signaling system was demonstrated using
Arabidopsis mutants defi cient in GPA1, the sole canonical Arabidopsis G subunit

expression (Zhang et al. 2011 ). Arabidopsis mutants defi cient in GPA1 were found
to be impaired in ABA inhibition of K + infl ux channels, and in pH-independent
activation of anion effl ux channels. The gpa1 mutants were disrupted both in ABA-
induced Ca 2+ -channel activation, and in production of reactive oxygen species
(ROS) in response to ABA. These studies further suggested that absence of GPA1
interrupts ABA signaling between ABA reception and ROS production, with a con-
sequent impairment in Ca 2+ -channel activation (Zhang et al. 2011 ). These results
strongly suggest that the heterotrimeric G-protein is involved in ABA signaling
system.

α

3.19.6 G-Proteins May Be Involved in Modulation

of ABA-Induced Stomatal Closure Immune Response

G-proteins may be involved in modulation of ABA-induced stomatal closure
immune response. ABA is known to be involved in stomatal pore closure which
is a key component in plant immune responses against bacterial pathogens
(Takahashi et al. 2007 ; Hettenhausen et al. 2012 ; Uraji et al. 2012 ). The