THE GERANYLGERANYL DIPHOSPHATE SYNTHASE GENE OF GIBBERELLA-FUJIKUROI - ISOLATION AND EXPRESSION

The rice pathogen, Gibberella fujikuroi, produces large amounts of gib berellins, a group of natural plant hormones, which induce the superel ongation (bakanae) disease of rice. Gibberellins are diterpenoid compo unds which are synthesized via the isoprenoid pathway. Here we report the isolation and molecular characterization of the geranylgeranyl dip hosphate synthase (ggs) gene from G. fujikuroi. Geranylgeranyl diphosp hate synthase is a key enzyme in isoprenoid biosynthesis. Southern blo t analysis showed that G. fujikuroi oi has a single copy of the ggs ge ne, which is not linked to the farnesyl diphosphate synthase gene. Thi s indicates that the genes of the isoprenoid pathway are not clustered in the fungal genome. The ggs gene is not interrupted by an intron an d codes for a polypeptide of 418 amino acids. Peptide sequence compari son 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 regulat ed by blue light. Ammonium and glucose did not affect the transcriptio n of the G. fujikuroi ggs gene, indicating that it is not subject to n itrogen and carbon catabolite repression. The G. fujikuroi gene comple ments a N. crassa al-3 mutant.