Abstract
The phytohormone abscisic acid (ABA) regulates physiologically important stress and developmental responses. To address the mechanism of ABA response, we isolated 4 novel ABA hypersensitive mutants named ahg (ABA hypersensitive germination). ahg2 showed clear ABA hypersensitivity not only in germination, but also at later developmental stages, and displayed pleiotropic phenotypes, small leaves, and short stems and roots. In ahg2, ABA was more accumulated and ABA-inducible genes were upregulated. Map-based cloning of AHG2 revealed that this gene encodes a poly(A)-specific ribonuclease is involved in mRNA destabilization and degradation. Detailed analysis of the ahg2 mutation suggests that this mutation causes reduced AHG2 expression. Interestingly, the expression of AHG2 was induced by treatments with ABA, high salinity, and osmotic stress. These results suggest that AHG2 has a pivotal role in the downregulation of some specific genes by destabilizing mRNAs to maintain proper ABA and stress responses.
