The geranylgeranyl diphosphate synthase gene of Gibberella fujikuroi: isolation and expression.

The rice pathogen, Gibberella fujikuroi, produces large amounts of gibberellins, a group of natural plant hormones, which induce the superelongation (bakanae) disease of rice. Gibberellins are diterpenoid compounds which are synthesized via the isoprenoid pathway. Here we report the isolation and molecular characterization of the geranylgeranyl diphosphate synthase (ggs) gene from G. fujikuroi. Geranylgeranyl diphosphate synthase is a key enzyme in isoprenoid biosynthesis. Southern blot analysis showed that G. fujikuroi has a single copy of the ggs gene, which is not linked to the farnesyl diphosphate synthase gene. This indicates that the genes of the isoprenoid pathway are not clustered in the fungal genome. The ggs gene is not interrupted by an intron and codes for a polypetide of 418 amino acids. Peptide sequence comparison showed a high degree of similarity to the corresponding Neurospora crassa gene (al-3). However, transcription analyses revealed that the ggs gene, in contrast to the analogous N. crassa gene, is not regulated by blue light. Ammonium and glucose did not affect the transcription of the G. fujikuroi ggs gene, indicating that it is not subject to nitrogen and carbon catabolite repression. The G. fujikuroi gene complements a N. crassa al-3 mutant.