Abstract
The hormonal action of abscisic acid (ABA) depends on the endogenous level of ABA which are controlled by the precise balance between its biosynthesis and catabolism. ABA is mainly catabolized into phaseic acid through 8'-hydroxylation. The enzyme ABA 8'-hydroxylase was shown to be a member of cytochrome P450 (P450), however, its gene had not been identified. Based on the phylogenetic analysis, DNA microarray analysis, and comparison with the rice genome, the candidate genes for this enzyme were narrowed down from among 272 Arabidopsis P450 genes. Functional expression of these genes in yeast revealed that members of CYP707A family, CYP707A1 through CYP707A4, code for the target ABA 8'-hydroxylase. Expression analysis showed that CYP707A2 is responsible for rapid decrease in ABA level during seed imbibition. cyp707a2 mutant phenotype confirmed this result. Furthermore, strong correlation was seen between mRNA level of these genes and the level of ABA during dehydration and rehydration conditions.
