Metabolism of gibberellins and ent-kaurenoids in mutants of Gibberella fujikuroi

The gibberellin precursors-ent-kaur-16-ene (1), ent-kaur-16-en-19-ol (2), ent-kaur-16-en-19-al (3) and ent-kaur-16-en-19-oic acid (4)- were fed to Gibberella fujikuroi gibberellin-defective mutants SG121, SG136, SG138 and SG139 in order to determine at which point their metabolic pathways were blocked. Mutant SG138 was also incubated with GA(4) and GA(14), and with 3 beta-hydroxyent-kaur-16-en-19-oic acid (10). Results indicated that SG139 was a regulatory mutant, and the synthesis of 1 was inhibited in SG121 and SG136. SG138 was blocked in the 1-->4 oxidation steps, as well as in the C-3 and C-13 hydroxylations and the C-20 loss. The complex phenotype showed by SG138 supports the hypothesis of a gene product involved in more than one biochemical oxidation step of the gibberellin biosynthesis. Biotransformation of GA(14) by SG(138) gave GA(36) and GA(37), providing new experimental evidence about the metabolism of GA(14) in Gibberella. Compound 10 was transformed to 3 beta,7 beta-dihydroxy-ent-kaur-16-en-19-oic acid, indicating that 3 beta-hydroxy group prevents enzymatic ring B contraction of ent-kaurenoids to gibberellins in strain SG138. (C) 1999 Elsevier Science Ltd. All rights reserved.