sti35, a stress-responsive gene in Fusarium spp.

A stress-induced mRNA was identified in the phytopathogenic fungus Fusarium oxysporum f. sp. cucumerinum. Treatment of the fungus with ethanol resulted in the induction of a major mRNA species encoding a protein of approximate Mr 37,000. A full-length cDNA clone of the induced message was obtained. RNA blot analysis indicated that the mRNA was induced by various other stresses, including treatment with copper(II) chloride and heat (37 degrees C). However, it was not greatly induced by treatment with phaseollinisoflavan, an antifungal isoflavonoid produced by Phaseolus vulgaris (French bean). In contrast, phaseollinisoflavan induced the homologous mRNA in the related bean pathogen Fusarium solani f. sp. phaseoli. A genomic clone of the F. solani f. sp. phaseoli gene was obtained, and both this and the cDNA clone from F. oxysporum f. sp. cucumerinum were sequenced. The latter indicated an open reading frame of 320 codons encoding a 34,556-dalton polypeptide. The corresponding reading frame in F. solani f. sp. phaseoli was 324 codons, 89% identical to the F. oxysporum f. sp. cucumerium sequence, and was interrupted by a short intron. The gene was designated sti35 (stress-inducible mRNA). Although computer homology searches were negative, the cloned gene was observed to cross-hybridize to DNAs of other filamentous fungi, Saccharomyces cerevisiae, and soybean. Thus, sti35 appears to be a common gene among a variety of eucaryotes.