NUCLEOTIDE-SEQUENCE VARIATION OF CHITIN SYNTHASE GENES AMONG ECTOMYCORRHIZAL FUNGI AND ITS POTENTIAL USE IN TAXONOMY

DNA sequences of single-copy genes coding for chitin synthases (UDP-N- acetyl-D-glucosamine:chitin 4-beta-N-acetylglucosaminyltransferase; EC 2.4.1.16) were used to characterize ectomycorrhizal fungi. Degenerate primers deduced from short, completely conserved amino acid stretches flanking a region of about 200 amino acids of zymogenic chitin syntha ses allowed the amplification of DNA fragments of several members of t his gene family. Different DNA band patterns were obtained from basidi omycetes because of variation in the number and length of amplified fr agments. Cloning and sequencing of the most prominent DNA fragments re vealed that these differences were due to various introns at conserved positions. The presence of introns in basidiomycetous fungi therefore has a potential use in identification of genera by analyzing PCR-gene rated DNA fragment patterns. Analyses of the nucleotide sequences of c loned fragments revealed variations in nucteotide sequences from 4 to 45%. By comparison of the deduced amino acid sequences, the majority o f the DNA fragments were identified as members of genes for chitin syn thase class II. The deduced amino acid sequences from species of the s ame genus differed only in one amino acid residue, whereas identity be tween the amino acid sequences of ascomycetous and basidiomycetous fun gi within the same taxonomic class was found to be approximately 43 to 66%. Phylogenetic analysis of the amino acid sequence of class II chi tin synthase- encoding gene fragments by using parsimony confirmed the current taxonomic groupings. In addition, our data revealed a fourth class of putative zymogenic chitin synthases.