Evolution of mating pheromone and receptor genes in Pucciniomycotina

Mating pheromones and their receptors act as a switch controlling phenotypic changes required for successful mating in fungi. Although basidiomycete mating pheromones and their processingwere first described in Rhodosporidiumtoruloides,
a “red yeast” in the Sporidiobolales, the receptor gene was never described,
and much of the mating process remains unexplored in any
species of Pucciniomycotina. We used published data from wholegenome-
sequencing projects to detect putative mating pheromones and
their receptor genes in several Pucciniomycotina. Primers were designed
for direct amplification and sequencing of a putative receptor
gene similar to Sterile 3 (ste3) and a closely linked gene similar to a putative
nuclear localization protein from other red yeasts. Results suggest
that pheromones and their receptors, as well as synteny around the
pheromone receptor locus, are relatively conserved in the Sporidiobolales.
Although only a single ste3 locus could be detected in Sporidiobolales
genomes, three separate loci similar to ste3 were detected in
the Puccinia graminis (Pucciniales) genome. In phylogenetic analyses
the Puccinia STE3 sequences formed a well-supported clade at the
base of the basidiomyceteswhile the Sporidiobolales sequences formed
a well-supported clade nested within the basidiomycetes.