3-Hydroxy-3-methylglutaryl-CoA reductase gene of Gibberella fujikuroi: isolation and characterization.

3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) is the first specific enzyme of the isoprenoid pathway, which leads to several classes of primary and secondary metabolites such as sterols, quinones, carotenoids and gibberellins. The structural gene of HMG-CoA reductase was isolated from the ascomycetous fungus Gibberella fujikuroi. Additionally, the most conserved region of this gene was also isolated from another plant pathogenic fungus, Sphaceloma manihoticola. Both ascomycetous fungi use the plant hormone gibberellin to induce an elongation of infected host plants, and in the case of S. manihoticola of plant tumors. Sequence analysis revealed a high degree of similarity between the deduced amino-acid sequences in the C-terminal catalytic domains of all known HMG-CoA reductases, but the highest degree was found between the sequences of both analysed ascomycetes. In contrast to Saccharomyces cerevisiae, Ustilago maydis and plants, G. fujikuroi and S. manihoticola possess only a single copy of this gene, although the product of HMGR (mevalonate) is the precursor for essential sterol and quinone biosynthesis and secondary metabolites such as gibberellins. RNA-blot and hybridization experiments showed that gene expression is not influenced by either glucose or ammonium excess.