Agriculture Reference
In-Depth Information
in the major ABA responses (Zhang DP, personnel communication), but two
other mutant alleles in the
CHLH
gene,
cch
and
rtl1
(for
rapid transcription
from
leaves
), show strong ABA-insensitive phenotypes in ABA-induced stoma-
tal closure and inhibition of stomatal opening (Shen et al.
2006
; Wu et al.
2009
;
Du et al.
2012
; Tsuzuki et al.
2011
,
2013
; Zhang et al.
2013
). These data sug-
gest that multiple ABA receptors are functioning in guard cells. Using three dif-
ferent methods, yeast two hybrid, chemical genetics, and coimmunoprecipitation
analysis, a cluster of homologous genes called RCAR/PYR/PYL was identified
as ABA receptors in
Arabidopsis
, and this family is composed of fourteen mem-
bers (Park et al.
2009
; Nishimura et al.
2010
; Ma et al.
2009
). Using biochemical
technique, ABA binding to RCAR/PYR/PRL was detected (Ma et al.
2009
; Park
et al.
2009
). Crystallographic structural study found that ABA enters a large inter-
nal cavity of PYR1 for ABA binding (Nishimura et al.
2010
). The overexpression
of
RCAR/PYR/PYL
leads to a slightly reduced stomata aperture in the absent of
ABA, and a strong hypersensitive phenotype in ABA-induced stomatal closure in
an ABA concentration-dependent manner compared to wild type in
Arabidopsis
(Ma et al.
2009
). The quadruple mutant
pyr1/pyl1/pyl2/pyl4
shows a strong ABA-
insensitive phenotype in ABA-induced stomatal closure, but the single mutant
pyr1
has no ABA-induced stomatal closure phenotype, indicating the presence of
functional redundancy within PYR/PYL/RCAR family. Further study is needed to
explore whether different types of ABA receptors function in guard cells in a cor-
porative manner to provide a mechanism to adjust the sensitivity of ABA percep-
tion for precise responses to drought and other stresses for an optimal stomatal
aperture and gas exchange (Ma et al.
2009
).
To investigate how ABA receptors deliver ABA signaling to downstream
components after binding to ABA, protein interaction analysis was performed,
and the direct protein interactions between ABA receptors RCAR/PYR/PYL and
phosphatases, PP2Cs, including HAB1, ABI1, ABI2, and PP2CA, were detected
by different groups (Ma et al.
2009
; Nishimura et al.
2010
; Park et al.
2009
),
and the phosphatase activity of PP2Cs was dramatically inhibited by the protein
interactions in an ABA concentration-dependent manner (Ma et al.
2009
; Park
et al.
2009
). Direct protein interactions between PP2C phosphatases and SnRK
family were also observed, the protein kinase activity of SnRKs was constitu-
tively released by the protein interactions, and the mutated PP2C phosphatases
failed to interact with and inhibit SnRKs (Umezawa et al.
2009
; Vlad et al.
2009
;
Weiner et al.
2010
; Dupeux et al.
2011
). Structural analysis confirmed the pro-
tein interaction of PP2C phosphatases with upstream ABA receptors and down-
stream SnRK kinases in protein complexes (Soon et al.
2012
; Santiago et al.
2012
). These series fantastic research formed a complete ABA signaling cas-
cade from ABA receptors to downstream ion channels for ABA-induced stoma-
tal closure. In this ABA signaling pathway, guard cells perceive ABA stimulus
by the binding of ABA to ABA receptors to further trigger the protein interac-
tion between ABA receptors and PP2Cs; this protein interaction inhibits the
phosphatase activity of PP2Cs and consequently releases the kinase activity of
SnRKs and CKPKs, which further activate anion channel SLAC1 by protein
Search WWH ::
Custom Search