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germination of seeds. Expression of different members
of the GmCYP707A family, A1a, A1b, A2b, A2c, A3a, A3b,
A4a, A4b and A5 , both in roots and in leaves, was
induced by drought stress, whereas transcription of A2a ,
A2b , A3b , A4a and A5 in roots, and only A3b and A5 in
leaves, was stimulated by rehydration. In addition,
short- or long-term salt stress induced expression of all
soybean CYP707A genes.
ABA catabolism might be affected by expression of
the soybean root-specific protein kinase, GmWNK1,
interacting with GmCYP707A1. Thus, the second effect
of the GmWNK1 on ABA could be related to metabo-
lism (Wang et al., 2010). Four homologues of CYP707A
(CYP707A 1-4) with major functions in ABA catabo-
lism were isolated from Arabidopsis (Kushiro et al.,
2004; Nambara & Marion-Poll, 2005). Sensitivity to
ABA or related stresses was increased with mutations
of these genes (Okamoto et al., 2006; Umezawa et al.,
2006). The mechanism of how the root-specific pro-
tein kinase acts on ABA or affects ABA dependence
under abiotic stress remains unclear. In the legume
Prosopis strombulifera low ABA hydroxylate levels were
detected under different salinity conditions (Llanes
et al., 2014). Control plants had a low dihydrophaseic
acid (DPA) content and usually no detectable phaseic
acid (PA), indicating that PA was rapidly metabolized.
Rapid metabolism of ABA is essential to prevent
accumulation of PA, and to regulate precisely stomatal
conductance (Nambara & Marion-Poll 2005). This is
consistent with a high content of DPA in the leaves of
P. strombulifera plants treated with Na 2 SO 4 (−2.6 MPa),
which also showed active production of free ABA and
ABA-GE. The biological activity of PA and DPA appears
to be very low. Previous studies showed that different
ABA-binding proteins in aleurone cells of barley are
unable to bind to PA, suggesting that this metabolite is
inactive in at least some physiological processes (Zhang
et al., 2001).
et al., 2010). Most of the studies of ABA receptors have
been done in Arabidopsis with a few reports in other
plants (Jia et al., 2011; Kim et al., 2012). Recently, ABA
receptors and group A 2C-type protein phosphatases
were shown to govern the ABA signalling pathway.
Moreover, recent studies have suggested that there are
interactions between the major ABA signalling pathway
and other signalling factors in stress responses and seed
and seedling development (Nakashima & Yamaguchi-
Shinozaki, 2013). Control of the expression of ABA
signalling factors may improve tolerance to environ-
mental stresses.
The PYR/PYL/RCAR family (hereafter referred to as
PYLs) is known to include ABA receptors. Ge et al.
(2010) reported the characterization of PYL homologues
(GmPYLs) in soybean. Twenty-three putative GmPYLs
can be found from the soybean genome sequence and
categorized into three subgroups. GmPYLs interact with
AtABI1 and two GmPP2Cs in diverse ways. Many of the
subgroup I GmPYLs interact with PP2Cs in an ABA-
dependent manner, whereas most of the subgroup II
and III GmPYLs bind to PP2Cs in an ABA-independent
manner. The subgroup III GmPYL23, which cannot
interact with any of the tested PP2Cs, differs from other
GmPYLs. The CL2/gate domain is crucial for GmPYL-
PP2C interaction, and a mutation in the conserved
proline (P109S) abolishes the interaction between
GmPYL1 and AtABI1. Furthermore, GmPYL1 interacts
with AtABI1 in an ABA-dependent manner in plant
cells. Three GmPYLs differentially inhibit AtABI1 and
GmPP2C1 in an ABA-dependent or -enhanced manner
in vitro . In addition, ectopically expressed GmPYL1
partially restores ABA sensitivity of the Arabidopsis triple
mutant pyr1/pyl1/pyl4. Thus, soybean GmPYLs are
ABA receptors that function by interacting and inhibit-
ing PP2Cs.
It has been demonstrated that a protein phosphory-
lation reaction in ABA signalling involves the
participation of several protein kinases (Verslues &
Zhu, 2007; Wang et al., 2010). The guard cell-specific
protein kinase AAPK from Vicia faba and its orthologue
OST1/SnRK2.6 in Arabidopsis are involved in ABA sig-
nalling (Yoshida et al., 2002; Rodriguez et al., 2010).
Expression of the soybean GmWNK1 is involved in
ABA signalling through activation of SPAK and OSR1
triggering a MAPK cascade or different co-transporters
regulating ABA-dependent osmotic stresses in legumes
(Wang et al., 2010)
10.3 perception of aBa in legumes
under abiotic stress
The cell needs to perceive ABA and transduce the signal
to cellular components for ABA function. Progress in
understanding ABA perception and signal transduction
has been achieved recently (Cutler et al., 2010;
Raghavendra et al., 2010; Umezawa et al., 2010; Weiner
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