A -Mating-Type Gene Expression Can Drive Clamp Formation in the Bipolar Mushroom Pholiota microspora (Pholiota nameko)

Abstract

In the bipolar basidiomycete Pholiota microspora, a pair of homeodomain protein genes located at the A-mating-type locus regulates mating compatibility. In the present study, we used a DNA-mediated transformation system in P. microspora to investigate the homeodomain proteins that control the clamp formation. When a single homeodomain protein gene (A3-hox1 or A3-hox2) from the A3 monokaryon strain was transformed into the A4 monokaryon strain, the transformants produced many pseudoclamps but very few clamps. When two homeodomain protein genes (A3-hox1 and A3-hox2) were transformed either separately or together into the A4 monokaryon, the ratio of clamps to the clamplike cells in the transformants was significantly increased to ca. 50%. We therefore concluded that the gene dosage of homeodomain protein genes is important for clamp formation. When the sip promoter was connected to the coding region of A3-hox1 and A3-hox2 and the fused fragments were introduced into NGW19-6 (A4), the transformants achieved more than 85% clamp formation and exhibited two nuclei per cell, similar to the dikaryon (NGW12-163 ؋ NGW19-6). The results of real-time reverse transcription-PCR confirmed that sip promoter activity is greater than that of the native promoter of homeodomain protein genes in P. microspora. Thus, we concluded that nearly 100% clamp formation requires high expression levels of homeodomain protein genes and that altered expression of the A-mating-type genes alone is sufficient to drive true clamp formation.In basidiomycetous mushrooms, mating compatibility is controlled by one or two sets of multiple allelomorphic genes known as bipolar or tetrapolar mating systems, respectively (37). In tetrapolar mushrooms, such as Coprinopsis cinerea (5, 13), Laccaria bicolor (8,11,19), and Schizophyllum commune (10), the mating-type loci A and B, which are located on different chromosomes, regulate mating and clamp formation (9,15,27,28). The A locus comprises multigenes encoding homeodomain proteins, and the B locus comprises multigenes encoding pheromones and pheromone receptor proteins (6,13,21,25,26,30,31,32,35,36). On the basis of the homeodomain sequence, the mating-type proteins of the A locus are divided into two subgroups: HD1 and HD2 (20,21). When an HD1 protein from one mate heterodimerizes with an HD2 protein from the other mate to form a functional regulatory protein, sexual compatibility is intracellularly recognized, and the A developmental pathway is initiated (3,17,23).Few studies have examined the composition and function of mating-type loci in bipolar basidiomycetes. In a landmark study, Bakkeren and Kronstad (2) discovered that in bipolar fungus, Ustilago hordei, the A-and B-mating-type loci were fused into one nonrecombining mating-type region with two alleles. However, subsequent studies revealed that although both A-and B-mating-type homologs are found in bipolar mushrooms, they are present on different chromosomes, and only the A-mating-type homologs are related to mating compatibility (1, 16).Although Ph...

The evolution and pathogenic mechanisms of the rice sheath blight pathogen

“…In Agaricomycetes, the two classes of genes (those encoding pheromone receptors and HD1/HD2 transcription factors) are part of the MAT locus in bipolar systems (Supplementary Note 10). In the R. solani AG1 IA genome, we found the homologous HD1 (AG1IA_06139) and HD2 (AG1IA_08558) sequences to Pleurotus djamor , and we detected similar HD1/HD2 specific domains according to the homologous motifs in Basidiomycetes40. In the assembly, we did not find diverged HD1 and HD2 mating type genes, which would be expected in a diploid basidiomycete.…”

Mating-Type Locus Organization and Mating-Type Chromosome Differentiation in the Bipolar Edible Button Mushroom Agaricus bisporus

“…bisporus H97 strain (as noted in a preliminary analysis [ 52 ]) and display several differences. The structure of the shorter gene β-fg1 with six introns (one after the start codon) and the length and amino-acid sequence of its protein are highly similar to the genes and proteins in C. cinerea [ 87 ], C. disseminatus [ 48 ], L. bicolor [ 86 ], Pholiota microspora [ 88 ] and Heterobasidion annosum [ 49 ]. The 220 aa-long product (ID 1137415) of β-fg1 shows 57–58% identity to the products of β-fg genes in C. disseminatus (AAZ14920), C. cinerea (EAU92782) and L. bicolor (EDR15176).…”

A Single Mating-Type Locus Composed of Homeodomain Genes Promotes Nuclear Migration and Heterokaryosis in the White-Rot Fungus Phanerochaete chrysosporium

“…Thus, it is likely that these functions are still controlled by the actions of pheromones and their receptors, but in the bipolar species, the MAT-A genes are now able to regulate the expression of these genes. More recently, Yi et al (85) showed that heteroallelism at MAT-A alone could drive both clamp cell formation and fusion in the bipolar species Pholiota microspora, suggesting some level of regulation of MAT-A genes on the normally MAT-B-regulated process of clamp cell fusion. Why loci controlling nuclear migration (MAT-B) should be regulated separately from the loci controlling conjugate nuclear division (MAT-A) is a longstanding mystery, as common MAT-A heterokaryons can form in tetrapolar species, but they produce a flat, unfit mycelium (62).…”