Abstract
In plants, under drought stress conditions, abscisic acid (ABA) levels increase, resulting in regulating the expression of many genes that function in the stress tolerance. In the presence of ABA, PYR/PYL/RCAR family START proteins that function as ABA receptors recognize and bind to group-A protein phosphatases 2C (PP2Cs). Then the subclass III of SNF1-related protein kinases (SnRK2s; SRK2D/SnRK2.2, 4SRK2E/SnRK2.6, and SRK2I/SnRK2.3) are released from the PP2C-dependent negative regulation, which allows SnRK2s to phosphorylate downstream transcription factors such as AREB/ABFs (AREB1/ABF2, AREB2/ABF4, and ABF3) and activate ABA-responsive gene expression or other ABA-related responses. In both srk2d srk2e srk2i and areb1 areb2 abf3 triple knockout mutants, the expression of the ABA-responsive genes such as group-A PP2Cs was drastically and globally impaired in comparison to the WT plants. Among the PP2Cs, three PP2C genes strongly induced in the vegetative tissues after exogenous ABA treatment were named HAI1, HAI2 and HAI3 (for highly ABA-induced PP2C genes). Here, we report the functional analysis of these HAI genes involved in drought stress response in Arabidopsis thaliana.
