OVEREXPRESSION OF 20-OXIDASE CONFERS A GIBBERELLIN-OVERPRODUCTION PHENOTYPE IN ARABIDOPSIS

In the gibberellin (CA) biosynthesis pathway, 20-oxidase catalyzes the oxidation and elimination of carbon-20 to give rise to C-19-GAs. All bioactive GAs are C-19-GAs. We have overexpressed a cDNA encoding 20-o xidase isolated from Arabidopsis seedlings in transgenic Arabidopsis p lants. These transgenic plants display a phenotype that may be attribu ted to the overproduction of CA. The phenotype includes a longer hypoc otyl, lighter-green leaves, increased stem elongation, earlier floweri ng, and decreased seed dormancy. However, the fertility of the transge nic plants is not affected. Increased levels of endogenous GA(1), GA(9 ), and GA(20), were detected in seedlings of the transgenic line exami ned. GA(4), which is thought to be the predominantly active GA in Arab idopsis, was not present at increased levels in this line. These resul ts suggest that the overexpression of this 20-oxidase increases the le vels of some endogenous GAs in transgenic seedlings, which causes the GA-overproduction phenotype.