Biology Reference
In-Depth Information
Regulation of Ca
2+
permeable channels
Regulation of anion channels
Phosphorylation of plasma membrane H
+
-ATPases
Activation of K
+
/H
+
-ATPase
Extracellular alkalinization
CDPK
Membrane depolarization
ROS generation
Activation of ethylene biosynthesis
Activation of abscisic acid signaling
Transcriptional activation of
PR
genes
Fig. 4.8
Immune signaling systems regulated by CDPKs
to be involved in regulation of anion- and Ca
2+
-permeable channels (Mori et al.
2006
). CDPKs regulate plasma membrane H
+
-ATPases by phosphorylation
(Schaller and Oecking
1999
). Anion channels and H
+
-ATPases have been shown
to be involved in Ca
2+
infl ux (Sanders et al.
2002
; White and Broadley
2003
). The
enzyme H
+
/K
+
-ATPase is a proton pump which is responsible for the acidifi ca-
tion of cytoplasm. The activation of K
+
/H
+
-ATPase is mediated by Ca
2+
infl ux and
activated by CDPK (Atkinson et al.
1990
). The CDPK may evoke ion fl uxes that
lead to extracellular alkalinization and depolarization of the plasma membrane
(Schaller and Oecking
1999
). The activation of the Ca
2+
channel by elicitors was
modulated by a heterotrimeric G-protein-dependent phosphorylation of the
channel protein in tomato, probably by activating a CDPK and inhibiting a pro-
tein phosphatase (Gelli and Blumwald
1997
). These results suggest that CDPK
targets several proteins involved in Ca2+ signaling system for phosphorylation
and activation.
CDPKs may be involved in activation of enzymes/proteins involved in various
defense signaling pathways (Fig.
4.8
). Plasma membrane-associated NADPH
oxidase is a substrate for CDPK (Xing et al.
2001
). NADPH oxidase is known to
stimulate ROS production (Kobayashi et al.
2007
). Overexpression of the
Arabidopsis
CDPK gene
AtCPK1
in a heterologous tomato protoplast system
resulted in an enhanced NADPH oxidase activity and increased production of ROS
(Xing et al.
2001
). Two CDPKs in potato, StCDPK4 and StCDPK5, phosphorylated
Ser-82 and Ser-97 in the terminus of StRBOHB, a potato NADPH oxidase, in a
calcium-dependent manner. Ectopic expression of the constitutively active mutant
of StCDPK5, StCDPK5VK, provoked ROS production in
Nicotiana benthamiana
leaves. The heterologous expression of StCDPK5VK phosphorylated Ser-82 of
StRBOHB in
N. benthamiana
(Kobayashi et al.
2007
). These results suggest that
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