Biology Reference
In-Depth Information
Activation of G- proteins
Activation of Ca
2+
channel opening
Increases in Ca
2+
influx
Activation of anion channels
Activation of K
+
channels
Phosphorylation -
regulated early
signaling events
Induction of NADPH oxidase
Generation of ROS
Regulation of H
+
-
ATPase activity
Redox signaling
Fig. 9.1
Phosphorylation/dephosphorylation - modulated PAMP-triggered early signaling events
with a bacterial PAMP (Gerber et al.
2006
). G-proteins may be involved in Ca
2+
channel opening (Gelli et al.
1997
). The activation of the Ca
2+
channel by PAMPs
was modulated by a heterotrimeric G-protein-dependent phosphorylation of the
channel protein in tomato, probably by activating protein kinase, and inhibiting
protein phosphatase (Gelli et al.
1997
). Protein phosphorylation precedes Ca
2+
infl ux in tobacco cells treated with a PAMP isolated from the oomycete pathogen
Phytophthora cryptogea
(Tavernier et al.
1995
). The G-proteins modulate the
phosphorylation/dephosphorylation system in the plasma membrane of tomato cells
and transduce the Ca
2+
infl ux signal (Vera-Estrella et al.
1994a
,
b
).
An elicitor-induced increase in H
+
- ATPase activity was shown to be activated by
the G-proteins in tomato (Vera-Estrella et al.
1994a
). G-protein has been shown to
activate a membrane-bound phosphatase that mediates the dephosphorylation of the
host plasma membrane H
+
-ATPase in tomato (Xing et al.
1997
). The dephosphory-
lation of H
+
-ATPase was followed by rephosphorylation by protein kinase and Ca
2+
-
dependent kinase (Xing et al.
1996
).
Anion channels are also activated by protein phosphorylation. Protein kinases act
as positive regulators, while phosphatases negatively regulate anion channel activity
(Pei et al.
1996
; Wendehenne et al.
2002
). The activated anion channels trigger
Ca
2+
-mediated signaling system (Ward et al.
1995
). Activation of K
+
channel by
phosphorylation has also been reported (Li et al.
1998
).
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