Genetic and Molecular Evidence of a Tetrapolar Mating System in the Edible Mushroom Grifola frondosa

Abstract

Grifola frondosa is a valuable edible fungus with high nutritional and medicinal values. The mating systems of fungi not only offer practical strategies for breeding, but also have far-reaching effects on genetic variability. Grifola frondosa has been considered as a sexual species with a tetrapolar mating system based on little experimental data. In the present study, one group of test crosses and six groups of three-round mating experiments from two parental strains were conducted to determine the mating system in G. frondosa. A chi-squared test of the results of the test-cross mating experiments indicated that they satisfied Mendelian segregation, while a series of three-round mating experiments showed that Mendelian segregation was not satisfied, implying a segregation distortion phenomenon in G. frondosa. A genomic map of the G. frondosa strain, y59, grown from an LMCZ basidiospore, with 40.54 Mb and 12 chromosomes, was generated using genome, transcriptome and Hi-C sequencing technology. Based on the genomic annotation of G. frondosa, the mating-type loci A and B were located on chromosomes 1 and 11, respectively. The mating-type locus A coded for the β-fg protein, HD1, HD2 and MIP, in that order. The mating-type locus B consisted of six pheromone receptors (PRs) and five pheromone precursors (PPs) in a crossed order. Moreover, both HD and PR loci may have only one sublocus that determines the mating type in G. frondosa. The nonsynonymous SNP and indel mutations between the A1B1 and A2B2 mating-type strains and the reference genome of y59 only occurred on genes HD2 and PR1/2, preliminarily confirming that the mating type of the y59 strain was A1B2 and not A1B1. Based on the genetic evidence and the more reliable molecular evidence, the results reveal that the mating system of G. frondosa is tetrapolar. This study has important implications for the genetics and hybrid breeding of G. frondosa.

Current Advances in the Functional Genes of Edible and Medicinal Fungi: Research Techniques, Functional Analysis, and Prospects

“…According to edible and medicinal fungi genetics, the A mating-type loci contain HD1 and HD2 genes encoding homology domain transcription factor proteins, which control behaviors such as the production of clamp connections, nucleus pairing, and division of the nucleus [117,118], whereas the B mating-type loci encode pheromone receptors and pheromone precursors, which control behaviors such as the migration of the nucleus and ablation of septa between cells [119]. The structure of the mating-type loci of common edible and medicinal fungi is shown in Figure 2 [120][121][122][123][124][125][126], which shows that the A mating-type loci contain a pair of mating-type genes that encode a pair of dissimilar homozygous proteins-HD1 and HD2; only at different alleles can they be paired to form heterodimers, whereas the B loci contain a pheromone receptor-coding gene and one to several pheromone-coding genes and originate from different alleles before they can recognize each other. From the perspective of collinearity, most of the A mating-type loci follow the typical mip-HD-β-fg structure, but L. edodes and F. filiformis do not, and the order and number of genes present at the loci vary considerably in different species, which possesses the characteristics of mating-type locus polymorphism.…”