Phylogenetic relationships of Pleurotus species according to the sequence and secondary structure of the mitochondrial small-subunit rRNA V4, V6 and V9 domains

A comparative study of the V4, V6 and V9 domains of the mitochondrial small -subunit (SSU) rRNA was conducted to evaluate the use of these sequences to investigate phylogenetic relatedness within the genus Pleurotus. The PCR p roducts encompassing these regions from 48 isolates belonging to 16 Pleurot us species were sequenced and compared. From this comparison, the length an d sequence of the three domains were found to be constant within a species. Significant inter-species variations due to insertion/deletion events were found, in most cases occurring in regions not directly involved in the mai ntainance of the standard SSU rRNA secondary structure. Phylogenetic analys is based upon these mitochondrial sequences was in agreement with relations hips previously established by morphological descriptions and with previous studies based upon the nuclear genome or isozymes; moreover such analysis resolved some ambiguities in earlier analyses. It was confirmed that P. ost reatus and P. florida represent a single species, as well as P. pulmonarius and P. sajor-caju. The phylogenetic analysis also made it possible to asse ss the relative positions of P. rattenburyi, P. lampas, P. sapidus, P. colo mbinus and P. eryngii. The results clearly showed that sequences of the V4, V6 and V9 domains of the mitochondrial SSU rRNA could provide good markers for use in the taxonomy and phylogeny of species of Basidiomycota. Because of their nucleotide conservation, the major advantage of these species-spe cific markers was the possibility to study only one isolate from each speci es to determine phylogenetic relatedness.