SPINDLY is involved in ABA signaling bypassing the PYR/PYLs/RCARs-mediated pathway and partly through functional ABAR

SPINDLY (SPY) is a putative O-linked β-N-acetyl glucosamine transferase and an O-fucosyltransferase, involved in various signaling pathways. We report here that SPY is involved in ABA signaling. spy mutants have insensitive phenotypes in response to ABA in seed germination and early seedling development. SPY has a complex relationship with ABI5, ABI3 and ABI4, which are key transcription factors in ABA-mediated seed germination and early seedling development. This relationship is dependent of developmental stage. Quadruple mutants ♀spy-3♂pyl1-1 pyl4-1 pyr1-1 and ♀pyl1-1 pyl4-1 pyr1-1♂spy-3 display enhanced insensitivity to ABA compared with either pyl1-1/pyl4-1/pyr1-1 or spy-3 in terms of seed germination and cotyledon greening. In RNA-seq assay, the general transcription level of germinating seeds of spy-3 under ABA is up-regulated compared with that of Col-0. The transcription level of ABAR，another ABA receptor spanning the chloroplast envelope, is up-regulated in spy-3 whereas another two types of putative ABA receptors ABAR and GTG1/GTG2 remain largely unaltered. As uncovered by genetic analyses, insensitivity to ABA of spy-3 is hindered by cch, a mutant of ABAR, in terms of seed germination and cotyledon greening, and vice versa. Genetic analyses also reveal that SPY regulates chloroplast function and leaf development via ABAR. Altogether, we conclude that SPY is involved in ABA signaling bypassing PYR-mediated pathway but likely playing a role in ABA signaling partly via the ABAR-mediated pathway.