Significance Abscisic acid (ABA) is a key stress-responsive hormone. Subgroup III Snf1-related kinase 2s (SnRK2s) are crucial positive regulators in ABA signaling pathway, but it is still not clear how SnRK2s are activated. In addition, besides ABA, some abiotic stresses can also activate SnRK2s with unknown mechanisms. Here we provide several lines of evidence to strongly support that brassinosteroid insensitive 2, a glycogen synthase kinase 3 (GSK3)-like kinase, interacts with and phosphorylates SnRK2s on specific novel sites to activate SnRK2s, which provides significant insights into the function of GSK3-like kinases in ABA signaling and transactivation of SnRK2s. Moreover, many GSK3-like kinases are regulated at transcriptional and/or posttranslational levels by many abiotic stresses, implying the presence of direct regulation of ABA signaling by other abiotic stresses.