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Fig. 17.2
Models of multiple interactions between ABA and other plant hormones in cold
stress response. There are multiple points of interaction between ABA and other plant hormones
including GA (
a
), cytokinin (
b
), ethylene (
c
), JA (
d
), and SA (
e
) in regulation of plant response
to cold stress.
CTK
cytokinin,
ETH
ethylene,
DELLA
DELLA protein,
AHK
Arabidopsis
histi-
dine kinase,
AHP
Arabidopsis
histidine phosphor-transferase,
ARR
Arabidopsis
response regu-
lator,
EIN3
Ethylene insensitive3,
JAZ
jasmonate-zim-domain protein,
MYC2
MYC-related
transcriptional activator2
responses in both ABA-dependent and ABA-independent signalling pathways
(Tran et al.
2007
); on the other hand, the homologous gene
AHK1
was identi-
fied as an osmotic stress sensor that positively regulates abiotic stress (Wohlbach
et al.
2008
; Kumar et al.
2013
; Tran et al.
2007
). Increasing evidence suggests a
negative role for cytokinin signalling in cold- and ABA-mediated abiotic stress.
For instance,
ahk2 ahk3
double mutants are highly tolerant to cold, drought, and
salt stress and show strong expression of ABA-responsive genes (Jeon et al.
2010
;
Tran et al.
2007
). However, whether cytokinin receptors can perceive stress signals
is still unclear. AHP2, AHP3, and AHP5 function as redundant negative regula-
tors of the drought stress response in both ABA-dependent and ABA-independent
manners (Nishiyama et al.
2013
). These studies support the notion that AHK2-
AHK4 and AHPs play negative roles under unfavourable environmental conditions
and may integrate with ABA signalling to modulate stress responses (Fig.
17.2
b).
Type-A
ARR
genes are negative response regulators in cytokinin signalling path-
way. They are induced by cytokinin as well as by cold stress (To et al.
2004
).
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