ABA-dependent and ABA-independent functions of RCAR5/PYL11 in response to cold stress

Arabidopsis thaliana has 14 abscisic acid (ABA) receptors--PYR1/PYLs/RCARs--which have diverse and redundant functions in ABA signaling; however, the precise role of these ABA receptors remains to be elucidated. Here, we report the functional characterization of RCAR5/PYL11 in response to cold stress. Expression of RCAR5 gene in dry seeds and leaves was ABA-dependent and ABA-independent, respectively. Under cold stress conditions, seed germination was markedly delayed in RCAR5-overexpressing (Pro35S:RCAR5) plants, but not in Pro35S:RCAR5 in ABA-deficient (aba1-6) mutant background. Leaves of Pro35S:RCAR5 plants showed enhanced stomatal closure--independent of ABA--and high expression levels of cold, dehydration, and/or ABA-responsive genes; these traits conferred enhanced freezing tolerance. Our data suggest that RCAR5 functions in response to cold stress by delaying seed germination and inducing rapid stomatal closure via ABA-dependent and ABA-independent pathways, respectively.