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system (catalase), nitric oxide (NO) signaling system (NO synthase [NOS]), mito-
gen-activated protein kinase (MAPK) cascade (MAPK phosphatases), transcription
factors (OsCBTs, WRKY7, MYB2, TGA3, CAMTAs, ethylene-responsive genes-
encoded proteins), glucosinolate metabolism (nuclear factors), and MLO proteins
(receptor-like protein/modulator of defense response).
4.14.2
CaM Binds to CNG Channel Protein
Cyclic nucleotide-gated ion channels (CNGCs) are involved in Ca
2+
-dependent sig-
naling pathways (Talke et al.
2003
; Yoshioka et al.
2006
). These channels have been
found to be CaM-binding proteins. CNGCs have a CaM-binding domain near the
C-terminus suggesting a role for CaM in modulating the activity of these channels
(Leng et al.
1999
). Calmodulin binding has been demonstrated for the
Arabidopsis
CNGC proteins AtCNGC1, AtCNGC2, and AtCNGC10 (Kohler et al.
1999
; Kohler
and Neuhaus
2000
; Borsics et al.
2007
).
Arabidopsis DND1
codes for a cyclic nucle-
otide-gated channel 2 (AtCNGC2) involved in plant defense responses (Clough et al.
2000
). In bean, three CNGC isoforms (PvCNGC-A, PvCNGC-B, and PvCNGC-C)
have been shown to be involved in defense responses. These proteins bound CaM in
a Ca
2+
-dependent manner. Expression of an isoform of CNGCs, PvCNGC was
induced, whereas the expression of two other isoforms PvCNGC -B and PvCNGC-C
was repressed in response to incompatible pathogens in bean. It suggests that there
may be functionally distinct role for each CNGC in plants (Ali et al.
2003
). CNGCs
constitute a link between cyclic nucleotide and Ca
2+
signals (Talke et al.
2003
). High-
affi nity CaM-binding site in tobacco plasma-membrane channel protein coincides
with cyclic nucleotide-binding domains (Arazi et al.
2000
).
4.14.3
Ca
2+
-ATPases as CaM-Binding Proteins
Ca
2+
-ATPases are localized in the endomembranes or plasma membrane. They play an
important role in removing Ca
2+
from the cytoplasm to terminate a signaling event (Sze
et al.
2000
; McAinsh and Pittman
2009
). Among the Ca
2+
-ATPases in plants, type IIB
Ca
2+
-ATPases are involved in Ca
2+
signaling. These ATPases bind with calmodulin acti-
vated by Ca
2+
. Ca
2+
-CaM interacts with type IIB ATPases to activate the pump by
releasing an autoinhibitory domain from the active site (Luan et al.
2002
).
4.14.4
Protein Kinases as CAM-Binding Proteins
Some protein kinases are regulated by CaMs. A chimeric plant Ca
2+
-CaM-dependent
protein kinase, CCaMK, with a visinin-like Ca
2+
binding domain and a CaM
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