Biology Reference
In-Depth Information
Type III CaM did not induce NAD kinase at any Ca
2+
level (Karita et al.
2004
). Ca
2+
spike frequency optimizes gene expression (Li et al.
1998
). Calcium oscillations
increase the effi ciency and specifi city of gene expression (Dolmetsch et al.
1998
).
A combination of changes in all Ca
2+
parameters produced by a particular signal
determines Ca
2+
signature (Luan et al.
2002
).
4.12
Ca
2+
Sensors in Ca
2+
Signal Transduction
The calcium signature is perceived by different Ca
2+
-binding proteins (Kudla et al.
2010
). These intracellular Ca
2+
-binding proteins are also known as Ca
2+
sensors.
The changes in [Ca
2+
]
cyt
concentrations are monitored by the Ca
2+
sensors and the
Ca
2+
signals are subsequently decoded and propagated downstream to activate plant
defense responses. Ca
2+
signaling pathways are composed of molecular relays; the
fi rst runner after Ca
2+
is Ca
2+
“sensor”, which monitors temporal and spatial changes
in Ca
2+
concentrations. Several Ca
2+
sensors have been identifi ed in plants (Fig.
4.4
).
Calmodulin
(CaM)
Calmodulin-like
proteins
Calcineurin B-
like (CBL)
proteins
Ca
2+
-dependent
and calmodulin-
independent
protein kinases
(CDPKs)
Calcium
sensors
Ca
2+
-CaM-
dependent kinases
(CCaMK)
NADPH oxidase
Copines
Phospholipase D
Fig. 4.4
Calcium-binding proteins as calcium sensors
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