Biosynthesis of gibberellins in Gibberella fujikuroi: biomolecular aspects

Gibberellins (GAs) are a large family of isoprenoid plant hormones, some of which are bioactive growth regulators, controlling seed germination, stem elongation and flowering. The rice pathogen Gibberella fujikuroi (mating po pulation C) is able to produce large amounts of GAs, especially the bioacti ve compounds gibberellic acid (GA(3)) and its precursors, GA(4) and GA(7). The main steps of the biosynthetic pathway have long been established from the identification of intermediates in wild-type G. fujikuroi and mutant st rains. However, the genetics of the fungus have been rather under-developed , and molecular genetic studies of the GA pathway started just recently. Th e progress in researching GA biosynthesis in the last 2 years resulted prim arily from development of the molecular tools, e.g, transformation systems for the fungus, and cloning the genes encoding GA biosynthesis enzymes, suc h as the bifunctional ent-copalyl diphosphate/kaurene synthase and several cytochrome P450 monooxygenases. The availability of these genes opened new horizons both for detailed study of the pathway and the regulation mechanis ms at the molecular level, and for modern strain improvement programs. This review gives a short overview of the well-known physiological and biochemi cal studies and concentrates mainly on the new molecular genetic data from GA research, including new information on the regulation of GA biosynthesis .