Control of Gibberellin Levels and Gene Expression during De-Etiolation in Pea

Gibberellin Al (GAl) levels drop significantly in wild-type pea (Pisum sativum) plants within 4 h of exposure to red, blue, or far-red light. This response is controlled by phytochrome A (phyA) (and not phyB) and a blue light receptor. GAs levels are increased in response to 4 h of red light, whereas the levels of GA19, GA2o, and GA29 do not vary substantially. Red light appears to control GAl levels by down-regulating the expression of Mendel's LE (PsGA30xl) gene that controls the conversion of GA20 to GAl' and by up-regulating PsGA2ox2, which codes for a GA 2-oxidase that converts GAl to GAs. This occurs within 0.5 to 1 h of exposure to red light. Similar responses occur in blue light. The major GA 20-oxidase gene expressed in shoots, PsGA20oxl, does not show substantial light regulation, but does show up-regulation after 4 h of red light, probably as a result of feedback regulation. Expression of PsGA30xl shows a similar feedback response, whereas PsGA2ox2 shows a feed-forward response. These results add to our understanding of how light reduces shoot elongation during de-etiolation.