Agriculture Reference
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some members of the signalling pathway. In the presence of ABA, the ABA receptor
PYR/PYL/RCAR (pyrabactin resistance/PYR1-like/regulatory component of ABA
receptor) forms a protein complex with PP2C, which activates OST1, making it pos-
sible for the ABA signal to be transmitted to the downstream components (Fujii et al.
2009
; Park et al.
2009
; Santiago et al.
2009
; Umezawa et al.
2009
). ABA-activated
OST1 acts upstream of ROS in guard cell ABA signalling.
To date, no complete description of a global transcriptomic study of any one
plant species' response to ROS has been published. The ROS-activated TFs that
have been revealed in plants are members of the WRKY, Zat, RAV, GRAS and
Myb families (Tripathy and Oelmller
2012
). Zat12 is an important component
of the oxidative stress-response signal transduction network of
Arabidopsis
,
the expression of which is induced by abiotic stresses and wound-induced sys-
temic signalling (Davletova et al.
2005
). Bioinformatics and chromatin immu-
noprecipitation (ChIP) approaches identified seven potential members of the
ROS-responsive elements (ROSEs). ROSE7/GCC was specifically bound by the
APETALA2/ethylene-responsive-element binding factor 6 (ERF6), and ERF6
interacts physically with mitogen-activated protein kinase 6 (MPK6) to regulate
ROS-responsive gene expression at the transcriptional level (Wang et al.
2013a
).
Activation of a MAPK cascade mediates responses to exogenous ABA and a vari-
ety of abiotic stress conditions in plants (Knetsch et al.
1996
; Hirt
2000
; Lu et al.
2002
). At least three members of the MAPK family in
Arabidopsis
—AtMPK3,
AtMPK4 and AtMPK6—can be activated by different stresses, including oxidative
stress (Kovtun et al.
2000
; Ichimura et al.
2000
; Yuasa et al.
2001
).
Given that ROS signals are tightly linked with abiotic and biotic stresses,
unravelling the mechanism of ROS regulation and the details of the genes induced
by ROS is important for deciphering ROS signals, which should ultimately con-
tribute to the development of high-quality crops.
10.4 Crosstalk Between ABA and ROS Signalling
Substantial effort has been expended on attempts to discover possible crosstalk
between ABA and ROS in plant stress damage and signalling upon exposure to differ-
ent stress conditions (Table
10.1
). For example, the time course of ABA accumulation
in the leaves of maize plants exposed to water stress was monitored at the same time
as the increased generation of ROS (such as O
2
−
and H
2
O
2
) and the induction of sev-
eral antioxidant enzymes (such as SOD, CAT, APX and GR) (Jiang and Zhang
2002
).
10.4.1 Stomatal Closure
Guard cells, which form stomata, have been investigated as a single-cell sys-
tem that is useful for the elucidation of individual signalling mechanisms that
function in the cellular signalling network. Given that ABA plays a key role in
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