Three nonorthologous ITS1 types are present in a polypore fungus Trichaptum abietinum.

To explore phylogenetic relationships of Trichaptum species, internal transcribed spacer (ITS) regions of nuclear ribosomal DNAs were sequenced and analyzed. Gene trees from ITS1 and ITS2 sequences showed striking discrepancy in relationships of eight T. abietinum strains. All strains of T. abietinum had a single orthologous ITS2 type, but there were three paralogous types in the ITS1 region, which were designated Types I, II, and III. PCR amplification tests using type-specific primers showed that Types I and II are present in all strains of T. abietinum. The results suggest that gene duplication of the ancestral ITS1 region might have occurred prior to evolutionary radiation of Trichaptum and both types have been maintained in Trichaptum. However, Type III was amplified only in three T. abietinum strains collected from Korea, indicating that a new local geographic subtype has arisen in Korean strains.