ABRE-BINDING FACTORS play a role in the feedback regulation of ABA signaling by mediating rapid ABA induction of ABA co-receptor genes.

Abstract

Group A protein phosphatase 2Cs (PP2Cs) are abscisic acid (ABA) co-receptors that negatively regulate the ABA signaling pathway by inhibiting the downstream SnRK2 protein kinases. It has long been observed that exogenous ABA treatments dramatically induce the expression of group A PP2C genes, but the underlying molecular mechanisms and the biological significance remain largely unknown. Here, by using GUS reporter transgenic lines in which various lengths of ABI1 and ABI2 promoters were used to drive GUS gene expression, we defined the promoter fragments that confer ABA inducibility to ABI1 and ABI2. We further showed that ABRE-binding factors (ABFs), the bZIP family transcription factors, directly bind to the promoters of group A PP2C genes, and mediate rapid induction of their expression on exogenous ABA treatments. Moreover, our data indicated that ABA dramatically induces the expression of ABF genes and the accumulation of endogenous ABF proteins, and that ABFs themselves are involved in this induction, thus providing another layer of ABA regulation towards ABF proteins in addition to the well-characterized ABA-induced phosphorylation by SnRK2 protein kinases. Together, our data demonstrate that ABFs mediate rapid ABA induction of group A PP2C genes, thus playing a role in the negative feedback regulation of ABA signaling.