Abstract
Abscisic acid (ABA) modulates numerous physiological events including seed dormancy and germination. I have studied the regulation of ABA metabolism and responses in Arabidopsis seeds. The ABA-insensitive abi3 mutants were isolated by a genetic screening based on germination ability in the presence of uniconazole that blocks gibberellin biosynthesis. The abi3 seeds failed to acquire desiccation tolerance, accumulation of seed reserves, and induction of seed dormancy. Phenotypic analysis suggested that ABI3 is a heterochronic gene that controls developmental timing during seed development. Gene expression analysis using randomly collected marker genes for seed development and germination indicated that ABI3 have a dual function both to activate and to repress gene expression. On the other hand, the ABA metabolism study revealed that four Arabidopsis CYP707A genes encode ABA 8'-hydroxylases, the major enzymes for ABA catabolism. Among them, the CYP707A2 was shown to be essential for the inactivation of ABA prior to seed germination.
