Biology Reference
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2008
,
2009
; Boller and He
2009
; Boller and Felix
2009
). The tobacco MAP kinase
SIPK is activated by the oomycete PAMP,
-megaspermin (Hall et al.
2007
). The
SIPK activation induced by the PAMP required external calcium infl ux, suggesting
that SIPK activation occurs downstream of Ca
2+
infl ux (Hall et al.
2007
). The signaling
cascade initiated by the endogenous elicitor AtPep1 leads to expression of
MPK3
gene involved in MAPK signaling system in a Ca
2+
-dependent manner (Qi et al.
2010
).
The MAPK, MPK6 has been shown to act downstream of cytosolic calcium signature
(Yue et al.
2012
).
β
4.21.4
Salicylate Signaling System
4.21.4.1
Ca
2+
Signature May Modulate SA Biosynthesis
and Accumulation Pathway
Salicylate (SA) signaling system has been identifi ed as an important downstream
event of Ca
2+
infl ux (Wang et al.
2010
; Boursiac et al.
2010
; Chen et al.
2011
;
Truman and Glazebrook
2012
). Ca
2+
signaling has been reported to play an impor-
tant role in modulation of salicylate signaling system (Du et al.
2009
; Wang et al.
2011
; Wan et al.
2012
). Ca
2+
infl ux plays an important role in triggering SA signal-
ing system (Garcia-Brugger et al.
2006
; Ahn et al.
2007
).
Cytosolic Ca
2+
signals result from a combined action of Ca
2+
infl ux through
channels and Ca
2+
effl ux through pumps and cotransporters (McAinsh and
Pittman
2009
; Ward et al.
2009
; Boursiac et al.
2010
). Infl ux occurs down the
electrochemical gradient through various ion channels, such as voltage-gated
channels or Ca
2+
-permeable cyclic nucleotide-gated channels (CNGCs) or gluta-
mate-gated ion channels (Qi et al.
2006
,
2010
; Moeder et al.
2011
; Vatsa et al.
2011
; Price et al.
2012
; Vincill et al.
2012
). Effl ux requires energy-dependent
Ca
2+
pumps (autoinhibited Ca
2+
-ATPases (ACAs) and ER-type Ca
2+
-ATPases)
(McAinsh and Pittman
2009
; Boursiac et al.
2010
). The cytoplasmic Ca
2+
signal
is shaped by the balance of activity between Ca
2+
infl ux and effl ux (Boursiac
et al.
2010
).
Disruption of the vacuolar calcium-ATPases in
Arabidopsis
results in the activa-
tion of salicylic acid signaling pathway, probably by generating specifi c Ca
2+
signa-
ture in the cytosol (Boursiac et al.
2010
). A double knockout mutation of the
vacuolar Ca
2+
pumps ACA1 and ACA11 in
Arabidopsis thaliana
resulted in the
activation of SA signaling system triggering programmed cell death. Initiation and
spread of hypersensitive response that protects plants from pathogens could also be
suppressed by disrupting the production of SA in
Arabidopsis
mutants with
combined
aca4/11
mutations and a
sid2
(for
salicylic acid induction-defi cient2
)
mutation. SID2 is an isochorismate synthase that is involved in biosynthesis of SA
(Wildermuth et al.
2001
). These studies suggest that disruption of the vacuolar
calcium-ATPases may result in the activation of
SID2
-mediated SA signaling path-
way (Boursiac et al.
2010
).
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