The Penicillium chrysogenum tom1 Gene a Major Target of Transcription Factor MAT1-1-1 Encodes a Nuclear Protein Involved in Sporulation

Three-Dimensional Structural Heteromorphs of Mating-Type Proteins in Hirsutella sinensis and the Natural Cordyceps sinensis Insect-Fungal Complex

The MAT1-1-1 and MAT1-2-1 proteins are essential for the sexual reproduction of Ophiocordyceps sinensis. Although Hirsutella sinensis has been postulated to be the sole anamorph of O. sinensis and to undergo self-fertilization under homothallism or pseudohomothallism, little is known about the three-dimensional (3D) structures of the mating proteins in the natural Cordyceps sinensis insect-fungal complex, which is a valuable therapeutic agent in traditional Chinese medicine. However, the alternative splicing and differential occurrence and translation of the MAT1-1-1 and MAT1-2-1 genes have been revealed in H. sinensis, negating the self-fertilization hypothesis but rather suggesting the occurrence of self-sterility under heterothallic or hybrid outcrossing. In this study, the MAT1-1-1 and MAT1-2-1 proteins in 173 H. sinensis strains and wild-type C. sinensis isolates were clustered into six and five clades in the Bayesian clustering trees and belonged to 24 and 21 diverse AlphaFold-predicted 3D structural morphs, respectively. Over three-quarters of the strains/isolates contained either MAT1-1-1 or MAT1-2-1 proteins but not both. The diversity of the heteromorphic 3D structures of the mating proteins suggested functional alterations of the proteins and provided additional evidence supporting the self-sterility hypothesis under heterothallism and hybridization for H. sinensis, Genotype #1 of the 17 genome-independent O. sinensis genotypes. The heteromorphic stereostructures and mutations of the MAT1-1-1 and MAT1-2-1 proteins in the wild-type C. sinensis isolates and natural C. sinensis insect-fungi complex suggest that there are various sources of the mating proteins produced by two or more cooccurring heterospecific fungal species in natural C. sinensis that have been discovered in mycobiotic, molecular, metagenomic, and metatranscriptomic studies, which may inspire future studies on the biochemistry of mating and pheromone receptor proteins and the reproductive physiology of O. sinensis.

The MAT1 locus is required for microconidia-mediated sexual fertility in the rice blast fungus

Rice blast fungus (Pyricularia oryzae) is a heterothallic ascomycete that causes the most destructive disease in cultivated rice worldwide. This fungus reproduces sexually and asexually, and its mating type is determined by the MAT1 locus, MAT1-1 or MAT1-2. Interestingly, most rice-infecting field isolates show a loss of female fertility, but the MAT1 locus is highly conserved in female-sterile isolates. In this study, we performed a functional analysis of MAT1 using the CRISPR/Cas9 system in female- and male-fertile isolates and female-sterile (male-fertile) isolates. Consistent with a previous report, MAT1 was essential for sexual reproduction but not for asexual reproduction. Meanwhile, deletion mutants of MAT1-1-1, MAT1-1-2, and MAT1-1-3 exhibited phenotypes different from those of other previously described isolates, suggesting that the function of MAT1-1 genes and/or their target genes in sexual reproduction differs among strains or isolates. The MAT1 genes, excluding MAT1-2-6, retained their functions even in female-sterile isolates, and deletion mutants lead to loss or reduction of male fertility. Although MAT1 deletion did not affect microconidia (spermatia) production, microconidia derived from the mutants could not induce perithecia formation. These results indicated that MAT1 is required for microconidia-mediated male fertility in addition to female fertility in P. oryzae .