Studies on the diversity of graminicolous Helminthosporium species by DNA analyzes and its taxonomical application

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The melanin biosynthetic pathway of Cochliobolus heterostrophus was analyzed. The Brn1 gene coding for reductase gene involved in melanin biosynthesis was cloned and sequenced. The Brn gene contains one open reading frame (804bp), consisting of 3 exons separated by two introns, and the predicted Brn1 polypeptide consists of 267 amno acids. The gene was contained only one copy per genome in this fungus.By using this gene, the taxonomical relationships in so-called graminicolous Helminthosporium species, Bipolaris, Curvularia, Drechslera, Exserohilum were analyzed. The Brn1 gene of some selected members in four genera was amplified with partial sequences derived from that of Cochliobolus heterostrophus as primers in PCR anc sequenced. Alignment of these sequences showed high similarities to each other through the entire sequence but intron regions.Neibour joining analysis using these sequences constructed four clusters. The cladogram well reflected the differentiation in this gene within these genera. However, relationships within these four genera differ from thosew based on morphological characters.Some other related studies on the plant pathogenic fungi were also summarized here.