PhyA and cry1 act redundantly to regulate gibberellin levels during de-etiolation in blue light

In pea (Pisum sativum L.) seedlings, both phytochrome A (phyA) and cryptochrome 1 (cry1) are required for the rapid inhibition of elongation in response to transfer from dark to blue light. The reduction in stem elongation upon blue light exposure is accompanied by a rapid reduction in the level of bioactive gibberellin A1 (GA1) in the shoot, and mutant studies indicate that this process is redundantly regulated by phyA and cry1. The reduction in GA1 levels under blue light may be mediated by phyA and cry1 in part through increased conversion of GA1 to the inactive catabolite GA8. Changes in the transcript level of key GA metabolism genes appear to play an important role in this process. Under blue light, both phyA and cry1 are required to suppress the transcript level of PsGA3ox1, which regulates the conversion of GA20 to GA1. PhyA and cry1 also contribute to upregulation of PsGA2ox2 transcript level under blue light, which encodes a GA 2-oxidase that converts GA1 to inactive GA8. In addition to changes in GA levels, phyA and/or cry1 may also regulate changes in GA responsiveness, an important mechanism for regulating long-term stem elongation in the light. Copyright © Physiologia Plantarum 2006.