Structure analysis of A and B mating type loci in a representative commercial strain of Pleurotus eryngii

Complete structures of the A3 and A4 alleles for the A mating type locus and the B3 and B4 alleles for the B mating type locus in the dikaryotic Pleurotus eryngii KNR2312, a representative commercial strain, were verified through comparative sequence analyses. Although the A3 mating type locus was highly homologous to the A4, it differed in the sequence region ranging from the 5'-region of homeobox (HB) motif of HD2 to the 5'-region of HB motif of HDI. Loss of 2 introns per gene was also observed in both the HDI and HD2 genes in the A3 locus. Investigation of the actinomycin o-treated samples revealed that the intronless HD2-A3 was more stable than the intron-containing HD genes, suggesting that the intron loss contributes to the stability of RNA transcript. When compared with the B3 mating type locus, the B4 mating type locus was shortened by 2.6 Kbp. It consisted of two mating pheromone receptor genes, STE3.3.2' and STE3.3.5, with the three associated mating pheromone genes (PHB3.5, PHB3.6, and PHB3.7) whereas the B3 locus was composed of three mating pheromone receptors, STE3.3.1, STE3.3.2, and STE3.3.4, with the four mating pheromone genes (PHB3.1-PHB3.4). STE3.3.3 devoid of associated pheromone gene was commonly discovered at the middle of both loci. STE3.3.1 and STE3.3.2 in the B3 showed high homology with STE3.3.2' in the B4, which suggests the occurrence of paralogous gene contraction in the sequence region spanning STE3.3.1-STE3.3.2 in the B3 mating type locus to generate STE3.3.2' in the B4. Lastly, specific primer sets targeting variable sequence regions in the mating type genes showed the successful detection of both mating types in P. eryngii, which contribute to the P. eryngii industry through acceleration of the breeding process.