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coupled signaling has been reported in tobacco cells treated with a bacterial PAMP
(Gerber et al.
2006
). The
Arabidopsis
G-protein GPA1 has been demonstrated to be
involved in the regulation of inward K
+
channels and slow anion channels (Wu and
Assmann
1994
; Wang et al.
2001
; Zhang et al.
2008
).
G-proteins are involved in PAMP-activated ROS-mediated signaling system
(Park et al.
2000
; Suharsono et al.
2002
). The PAMP fl g22 induces G-protein-
activated ROS signaling systems. The gene
AGB1
, encoding the
-subunit of
G-protein in
Arabidopsis
, is highly induced after fl g22 treatment (Zipfel et al.
2004
).
The
agb1
mutants are impaired in the oxidative burst triggered by fl g22, suggesting
the importance of G-proteins in ROS signaling system (Ishikawa
2009
). G-proteins
have been shown to be involved in generation of NO which is involved in stomatal
closure immune responses (Li et al.
2009
; He et al.
2013
). G-protein induces
biosynthesis of the important second messenger polyamine (Fujiwara et al.
2006
).
The G-protein may be involved in generation of phospholipid second messengers
(Viehweger et al.
2006
). G-proteins are also involved in salicylate signaling system
(Sano et al.
1994
; Beffa et al.
1995
; Fujiwara et al.
2006
), jasmonate signaling
system (Zhao and Sakai
2003
; Trusov et al.
2006
), ethylene signaling system
(Fujiwara et al.
2006
; Steffens and Sauter
2010
), abscisic acid signaling system
(Liu et al.
2007a
; Gao et al.
2010a
,
b
), gibberellic acid signaling system (Gao et al.
2010a
,
b
), brassinosteroid signaling system (Oki et al.
2009
), and auxin signaling
systems (Gao et al.
2010b
).
β
3.2
Heterotrimeric G-Protein Signaling
3.2.1
Subunits of Heterotrimeric G-Proteins
The heterotrimeric G-proteins contain G
- subunits (Fujisawa
et al.
2001
; Temple and Jones
2007
; Trusov et al.
2008
,
2010
; Wang et al.
2008
;
Zhang et al.
2011
). G
α
-, G
β
-, and G
γ
β
and G
γ
are tightly associated as a functional unit, while
G
α
can signal independently or through G
βγ
(Zeng et al.
2007
). In
Arabidopsis
genome only one gene is present for the G
subunits (Mason and Botella
2001
; Assmann
2002
; Zeng et al.
2007
), while three genes have been identifi ed
for G
α
and G
β
subunits (Chakravorty et al.
2011
, Thung et al.
2012
). In addition to a
single prototypical G
γ
-like
proteins, known as Extra Large G-protein 1 (XLG1), XLG2, and XLG3 (Ding
et al.
2008
; Zhu et al.
2009
). The rice genome harbors one gene for each of G
α
protein (GPA1),
Arabidopsis
has three unique G
α
α
(
RGA1
) and G
(RGG1 and RGG2) (Kato et al.
2004
).
TaGA1
and
TaGA2
genes encoding G-protein
β
(
RGB1
) and two genes for G
γ
α
subunits have been cloned
from wheat (Hossain et al.
2003
). Four G
proteins have
been detected in soybean (Bisht et al.
2011
). Choudhury et al. (
2011
) identifi ed
10 G
α
, four G
β
, and two G
γ
proteins and these can be grouped into three distinct families based on
sequence features: the archetypal G
γ
γ
proteins, the prenylation-less G
γ
proteins
and the cysteine-rich G
γ
proteins.
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