Separate compartments for the production of sterols, carotenoids and gibberellins in Gibberella fujikuroi

Substrate flow in the sterol, carotenoid and gibberellin pathways of Gibberella fujikuroi were examined by isotope-dilution experiments. The wild type and two carotenoid mutants of this fun were grown in minimal medium with abundant glucose. limiting ammonium nitrate and a radioactively labelled precursor (either acetate, mevalonate or leucine). The precursors did not affect growth or terpenoid production, with two exceptions; leucine allowed additional growth, as expected from the nitrogen limitation In the medium, and mevalonate inhibited the accumulation of gibberellins, but only if added before the onset of gibberellin production. The relative contributions of glucose, mevalonate, leucine and acetate as terpenoid precursors, calculated from tire specific radioactivities of ergosterol, neurosporaxanthin and phytoene, were different products and different precursors. We conclude that the biosyntheses of sterols, gibberellins and carotenoids in Gibberella are physically separated in different subcellular compartments with independent substrate pools. The same results were obtained with the three strains, except for carotenoid production, indicating that this pathway is regulated independently from other terpenoid pathways.