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 pr imary and secondary metabolites such as sterols, quinones, carotenoids and gibberellins. The structural gene of HMG-CoA reductase was isolat ed from the ascomycetous fungus Gibberella fujikuroi. Additionally, th e most conserved region of this gene was also isolated from another pl ant pathogenic fungus, Sphaceloma manihoticola. Both ascomycetous fung i use the plant hormone gibberellin to induce an elongation of infecte d host plants, and in the case of S. manihoticola of plant tumors. Seq uence analysis revealed a high degree of similarity between the deduce d amino-acid sequences in the C-terminal catalytic domains of all know n HMG CoA reductases, but the highest degree was found between the seq uences of both analysed ascomycetes. In contrast to Saccharomyces cere visiae, Ustilago maydis and plants, G. fujikuroi and S. manihoticola p ossess only a single copy of this gene, although the product of HMGR ( mevalonate) is the precursor for essential sterol and quinone biosynth esis and secondary metabolites such as gibberellins. RNA-blot and hybr idization experiments showed that gene expression is not influenced by either glucose or ammonium excess.