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Ca
2+
influx
Cytosolic Ca
2+
CDPK
ACC synthase
Ca
2+
signature
1-Aminocyclopropane-1-
carboxylic acid (ACC)
ACC oxidase
Activation
Ethylene
Fig. 4.13
Ca
2+
infl ux and calcium-dependent protein kinase (CDPK) in downstream biosynthesis
of ethylene
and basic PR-1 protein families and chitinase accumulation were found to be
inhibited by EGTA, the Ca
2+
chelator. Addition of calcium or application of Ca
2+
ionophore induced the ethylene-inducible defense-related proteins (Raz and Fluhr
1992
). These results suggest that downstream ethylene signaling system is triggered
by Ca
2+
signature.
4.21.7
Abscisic Acid Signaling System
Arabidopsis
CDPK AtCPK32 interacts with ABF4, a transcriptional regulator of
ABA-responsive gene expression, and modulates its activity (Choi et al.
2005
).
Expression of a grape CDPK, ACPK1, in
Arabidopsis thaliana
activates abscisic
acid (ABA) signaling (Yu et al.
2006
,
2007
). Analysis of transcriptome changes in
Arabidopsis
revealed 230 calcium-responsive genes, of which 162 were upregulated
and 68 were downregulated. Analysis of upstreams revealed, exclusively in the
upregulated genes, a highly signifi cant occurrence of a consensus sequence
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