Regulation of Gibberellin 20-Oxidase and Gibberellin 3β-Hydroxylase Transcript Accumulation during De-Etiolation of Pea Seedlings

Gibberellin (GA) 20-oxidase (GA 20-ox) and GA 3β-hydroxylase (GA 3β-hy) are enzymes that catalyze the late steps in the formation of active GAs, and are potential control points in the regulation of GA biosynthesis by light. We have investigated the photoregulation of the GA 20-ox and GA 3β-hy transcript levels in pea (Pisum sativum L.). The GA 20-ox transcript level was higher in light-grown seedlings than in etiolated seedlings, whereas GA 3β-hy mRNA accumulation was higher in etiolated seedlings. However, transfer of etiolated seedlings to light led to a 5-fold increase in the expression of both transcripts 4 h after transfer. GA 20-ox mRNA accumulation is regulated by both phytochromes A and B. Transfer to light also resulted in a 6-fold decrease in GA(1) levels within 2 h. These results suggest that the light-induced drop in GA(1) level is not achieved through regulation of GA 20-ox and GA 3β-hy mRNA accumulation. The application of exogenous GA(1) to apical buds of etiolated seedlings prior to light treatments inhibited the light-induced accumulation of both GA 20-ox and GA 3β-hy mRNA, suggesting that negative feedback regulation is an important mechanism in the regulation of GA 20-ox and GA 3β-hy mRNA accumulation during de-etiolation of pea seedlings.