Biology Reference
In-Depth Information
9.10
Phosphorylation of Proteins Involved in H
+
Fluxes
Induced by PAMP/Elicitor
An important target protein of CDPK for phosphorylation is plasma membrane
H
+
-ATPase (Piedras et al.
1998
). Elicitation of tobacco cell cultures with an elicitor
resulted in changes of H
+
fl uxes, detectable as media alkalinization. These fl uxes are
accomplished by way of inactivation of an H
+
-ATPase by CDPK (Piedras et al.
1998
). Reversible phosphorylation of an H
+
-ATPase in tobacco has been reported
(Xing et al.
1996
). CDPKs are known to regulate H
+
-ATPase (Camoni et al.
1998b
;
Schaller and Oecking
1999
). A CDPK phosphorylates H
+
-ATPase of oat roots
(Schaller et al.
1992
).
Regulation of H
+
-ATPases appear to depend on the presence or absence of 14-3-3
proteins (Chung et al.
1999
; Fuglsang et al.
1999
). An in vitro interaction between
a phosphorylated CDPK and 14-3-3 isoforms from
Arabidopsis
has been reported
(Camoni et al.
1998a
). There may be a functional link among phosphorylated
CDPK, H
+
-ATPase and 14-3-3 protein in defense signaling (Romeis et al.
2000
).
Binding of 14-3-3 proteins to the plasma membrane H
+
-ATPase involves the three
C-terminal residues Tyr-Thr-Val and requires phosphorylation of Thr (Fuglsang
et al.
1999
). 14-3-3 proteins recognize phosphate-bearing amino acids and regulate
the H
+
-ATPase enzyme activity (Romeis et al.
2000
).
9.11
Phosphorylation of Proteins Involved
in ROS Signaling System
Several and different protein kinases induce a sequence of phosphorylation events
in the production of reactive oxygen species (ROS) and downstream signaling
events (Fig.
9.2
; Anthony et al.
2006
). Elicitors induce very rapid production of
ROS resulting in the oxidative burst in plant cells. The oxidative burst is mostly
mediated by NADPH oxidases (Torres et al.
2002
; Torres and Dangl
2005
; Davies
et al.
2006
). In response to elicitors,
Arabidopsis
leaves produce ROS within
minutes and this oxidative burst peaks around 10 min. During this period, phos-
phorylation on several different residues in a NADPH oxidase (RBOHD [respira-
tory burst oxidase protein D]) was observed (Benschop et al.
2007
). CDPK has been
shown to phosphorylate NADPH oxidase (Xing et al.
1997
; Blumwald et al.
1998
).
Accumulation of ROS requires Ca
2+
infl ux and protein kinase activity (Keller et al.
1998
; Piedras et al.
1998
; Romeis et al.
1999
).
Anthony et al. (
2006
) reported the participation of 3-phosphoinositide-dependent
protein kinase 1 (PDK1), the AGC family protein kinase called oxidative signal-
inducible 1 (OXI1) protein kinase, the serine/Thr kinase (PTI1-2 for
Pt
o kinase
i
nteractor1-2), and the mitogen-activated kinase MPK6 in ROS signaling system in
A. thaliana
. OXI1 was identifi ed as a downstream signaling component to the
PDK1 (Rentel et al.
2004
). OXI1 is activated by PDK1-mediated phosphorylation
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