Separate Compartments for the Production of Sterols, Carotenoids and Gibberellins in Gibberella fujikuroi

Abstract

Substrate flows 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 fungus 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 the specific radioactivities of ergosterol, neurosporaxanthin and phytoene, were different for 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.

On the absence of the glyceraldehyde 3-phosphate/pyruvate pathway for isoprenoid biosynthesis in fungi and yeasts

“…Similar feeding experiments performed with Gibberella fujikuroi, indicated that such a compartmentation also occurred in this fungus for the formation of ergosterol, carotenoids and gibberellins [7]. Such radiolabeling experiments, however, even if they were in accordance with the role of MVA as precursor, do not exclude the participation of other possible pathways to IPP.…”

“…This suggested that they were all issued from a single acetyl-CoA pool. The di¡erences observed in the incorporation of radiolabeled acetate, MVA or leucine into di¡er-ent isoprenoid series of Phycomyces blakesleeanus and Gibberella fujikuroi [6,7] actually re£ected the compartmentation of the MVA pathway in the fungal cells and were therefore most probably not related to the presence of two di¡erent routes to IPP as observed in higher plants. …”

“…Although the presence of the MVA route was well established in several fungi and yeasts for many isoprenoids, no data were available for the biosynthesis of their ubiquinone. Radiolabeling experiments suggested even that the biosynthesis of L-carotene and ergosterol in Phycomyces blakesleeanus [6] or of ergosterol, carotenoids and gibberellins in Gibberella fujikuroi [7] were independently regulated and occurred in di¡erent, physically separated subcellular compartments from independent substrate pools.…”

Regulation of Carotenogenesis and Secondary Metabolism by Nitrogen in Wild-Type Fusarium fujikuroi and Carotenoid-Overproducing Mutants

“…This is followed by the synthesis of isopentenyl diphosphate (IPP) and several condensation steps, the latter mediated by a prenyl transferase presumably shared by both pathways and encoded by fppS (23), to yield farnesyl diphosphate (FPP). From this point, separate specific enzymes, encoded by genes ggs1 (31) and gibA (originally ggs2 [45]), are used to produce the common precursor geranylgeranyl diphosphate (GGPP) in different subcellular locations (15). The biosynthesis of gibberellins depends on seven genes organized in a cluster (44).…”

Gibberellin biosynthesis inGibberella

“…3). This implies that the biosyntheses of the three groups ofterpenoids are physically separated in subcellular compartments (Domenech et al, 1996). Similar experiments indicated that the biosyntheses of carotenes and sterols are physically separated and independently regulated in the fungus Phycomyces blakesleeanus (Bejarano & Cerda-Olmedo, 1992).…”