Regulation of the early GA biosynthesis pathway in pea.

The early steps in the gibberellin (GA) biosynthetic pathway are controlled by single copy genes or small gene families. In pea (Pisum sativum L.) there are two ent-kaurenoic acid oxidases, one expressed only in the seeds, while ent-copalyl synthesis and ent-kaurene oxidation appear to be controlled by single copy genes. None of these genes appear to show feedback regulation and the only major developmental regulation appears to be during seed development. During shoot maturation, transcript levels do not change markedly with the result that all the three genes examined are expressed in mature tissue, supporting recent findings that these tissues can synthesise GAs. It therefore appears that the regulation of bioactive GA levels are determined by the enzymes encoded by the 2-oxoglutarate-dependent dioxygenase gene families controlling the later steps in GA biosynthesis. However the early steps are nonetheless important as a clear log/linear relationship exists between elongation and the level of GA1 in a range of single and double mutants in genes controlling these steps.