Biology Reference
In-Depth Information
regulates Ca
2+
release by enhancing InsP3 receptor binding affi nity for InsP3.
Overexpression of RACK1 markedly augments Ca
2+
release, while depletion of
RACK1 by interference RNA diminishes Ca
2+
release (Patterson et al.
2004
).
InsP3-activated Ca
2+
channel is the important Ca
2+
release channel (Alexandre
and Lassales
1992
). InsP3-gated channels release Ca
2+
from the vacuole and
endoplasmic reticulum (ER) (Berridge
1993
). The calcium released through this
channel induces calcium waves and oscillations in the cytosol (Berridge
1993
).
Calcium ion acts as a signal carrier (Kudla et al.
2010
) and calcium signaling is
modulated by specifi c “calcium signatures”. The specifi c changes in calcium
transients, oscillations, or repeated spikes/waves are called calcium signatures
(Lecourieux et al.
2006
). Collectively the results suggest that G-protein triggers
the InsP3-activated Ca
2+
channel and modulates Ca
2+
signature - mediated
immune signaling system.
3.10.2
G-Proteins Stimulate H
+
-ATPase and Regulate
Ca
2+
Channel
PAMP-PRR signaling activates G-proteins and the activated G-proteins stimulate
the plasma membrane H
+
-ATPase (Vera-Estrella et al.
1994a
,
b
; Xing et al.
1997
;
Blumwald et al.
1998
). The plasma membrane H
+
-ATPases generate an H
+
-gradient
across the plant plasma membrane. The concomitant hyperpolarization of the mem-
brane potential induces the opening of the Ca
2+
channel. The proton gradient creates
an electrical potential, which drives Ca
2+
uptake through ion channels (Palmgren
and Harper
1999
). The results suggest that the G-proteins may also modulate the
expression of H
+
-ATPase and activate Ca
2+
signaling.
3.10.3
G-Proteins Activate Ca
2+
Signaling System Through
Modulation of Phosphorylation/Dephosphorylation
System
G-proteins may be involved in Ca
2+
channel opening (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 signal (Vera-Estrella et al.
1994a
).
Phosphorylation of proteins involved in G-protein coupled signaling has been
reported in tobacco cells treated with a bacterial PAMP (Gerber et al.
2006
).
The activation of the Ca
2+
channel by PAMPs was modulated by a heterotri-
meric G-protein-dependent phosphorylation of the channel protein in tomato,
probably by activating protein kinase, and inhibiting protein phosphatase (Gelli
et al.
1997
). The activated G-protein transduced the signal by activating
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