A Study On Regulatory Mechanism Of Arabidopsis GSK3 In Abscisic Acid Signaling

Arabidopsis Glycogen Synthase Kinase 3 (GSK3)-like kinases have versatile functions in plant development and in responding to abiotic stresses. Although physiological evidence suggested a potential role of GSK3-like kinases in abscisic acid (ABA) signaling, the underlying molecular mechanism was largely unknown. Here, we identified members of Snf1-Related Kinase 2s, SnRK2.2 and SnRK2.3 can interact with and be phosphorylated by a GSK3-like kinase, Brassinosteroid Insensitive 2 (BIN2). bin2-3 bil1 bil2, a loss of function mutant of BIN2 and its two closest homologues BIN2 like 1(BIL1) and BIN2 like 2(BIL2), was hyposensitive to ABA in both primary root inhibition, ABA-responsive gene expression, and in-gel kinase assay on phosphorylating ABF2 fragment, while bin2-1, a gain of function mutation of BIN2 was hypersensitive to ABA, suggesting these GSK3-like kinases function as positive regulators in ABA signaling. Furthermore, BIN2 phosphorylated SnRK2.3 on T180, and SnRK2.3T180A had decreased kinase activity in both autophosphorylation and phosphorylating ABRE binding factors. Bikinin, a GSK3 kinase inhibitor, inhibited the SnRK2.3’s kinase activity and its phosphorylation on T180 in vivo. Our genetic analysis further demonstrated that BIN2 regulating ABA signaling downstream of the PYRABACTIN RESISTANCE1 (PYR1)/PYR1-LIKE (PYL)/REGULATORY COMPONENTS OF ABA RECEPTORS (RCAR) receptors and clade A Protein Phosphatase 2C (PP2C), but relies on SnRK2.2 and SnRK2.3. These findings provide significant insight into the modulation of ABA signaling by Arabidopsis GSK3-like kinases.