Abstract
Analysis of gibberellin (GA)-deficient dwarf mutants contributed to the identification of GA biosynthesis genes. Meanwhile, additional GA-related genes that have not been discovered by conventional forward genetic approach are likely to be present. We identified such genes by analysis of an activation tagged mutant (1), and by reverse genetic approach (2). (1) A dominant dwarf mutant designated dwarf and delayed-flowering 1 (ddf1) was isolated from a library of activation-tagged Arabidopsis. We found that the contents of bioactive GAs were decreased in ddf1. Genetic and molecular analyses revealed that the ddf1 phenotypes are caused by increased expression of GA 2-oxidase 7 gene (GA2ox7), which encodes a C_<20>-GA inactivation enzyme, through increased expression of a high salinity responsive AP2 transcription factor, DDF1. (2) A rice P450 gene, EUI (CYP714D1) encodes a novel class of GA inactivation enzyme, which catalyzes 16α, 17-epoxidation of GAs. We examined the possible involvement of other CYP714 members of Arabidopsis and rice in GA metabolism. We found the gene products that have GA 13-hydroxylation activity from Arabidopsis (one gene) and rice (two genes). GA measurements of a rice double mutant of these genes indicated that the levels of 13-hydroxy GAs were decreased, whereas those of non 13-hydroxy GAs were increased in the double mutants. These results strongly suggest that these two cytochrome P450 genes play a major role in GA 13-hydroxylation in rice.
