Structure and Biological Significance of Mating Type Locus in Edible Mushrooms

摘要

Three studies are presented here. In the first, we characterized the gene for the homeodomain protein (hox1) in a bipolar mushroom, Pholiota microspora, which is a putative homologue of A mating type genes in tetrapolar mushrooms. We also sequenced and characterized the gene for the pheromone receptor (rcb1) in P. microspora, which is a putative homologue of the B mating type genes in tetrapolar mushrooms. The hox1 gene was mapped to the A locus in linkage group I. However, rcb1 was not linked to the A locus and was mapped to another linkage group. In the second study, we investigated the genomic structure of the P. microspora A locus and its flanking region. A second homeodomain protein gene (A4-hox2) was discovered upstream of AA-hox1. In the third study, we used a DNA-mediated transformation system in P. microspora to investigate the homeodomain proteins that control the clamp-cell formation. When a single homeodomain protein gene (A3-hox1 or A3-hox2) from the A3 monokaryon strain was transformed into the AA monokaryon strain, the transformants produced many pseudo-clamps but very few clamps. When two homeodomain protein genes (A3hox1 and A3-hox2) were transformed either separately or together into the AA monokaryon, the ratio of clamps to the clamp-like cells in the transformants was significantly increased to approximately 50%. We, therefore, concluded that the dosage of homeodomain protein genes is important for clamp-cell formation. When the sip promoter was connected to the coding region of A3-hox1 and A3-hox2 and the fused fragments were introduced into A4 monokaryon, the transformants achieved more than 85% clamp formation and exhibited two nuclei per cell, similar to the dikaryon. So, we concluded that nearly 100% clamp formation requires high expression levels of homeodomain protein genes and that only A genes control the clamp-cell formation.