Investigations into the taxonomy of the mushroom pathogen Verticillium fungicola and its relatives based on sequence analysis of nitrate reductase and ITS regions

Abstract

The full sequence of the nitrate reductase gene was obtained from a type isolate of Verticilliumfungicola var. fungicola and used for phylogenetic analysis against other ascomycete fungi. Sequencing obtained 2749 bp of coding region, 668 bp of 5' flanking sequence and 731 bp of 3' flanking sequence. In silico analysis indicated that the coding region contains a single intron and translates into an 893 amino acid protein, with BLAST analysis identifying five conserved nitrate reductase domains within the protein. The 5' flanking sequence contains numerous conserved sites putatively involved in binding nitrogen regulatory proteins, indicating that the regulation of the gene is likely to be subject to the same regulation as that of model fungi such as Aspergillus nidulans. The central portion of this gene was amplified and sequenced from a number of V.fungicola isolates and related fungi and the resulting phylogenies compared to those obtained from analysis of the rDNA internal transcribed spacer regions for these fungi. Both nitrate reductase and ITS analyses provide additional evidence that reinforces previous findings that suggest the mushroom pathogenic Verticillium species are more related to other chitinolytic fungi such as the insect pathogens Verticillium lecanii and Beauveria bassiana than to the plant pathogenic Verticillia.