The MATαHMGbox and HMG-boxROX1-like domains of the MAT1-1-1 and MAT1-2-1 proteins, respectively, play essential roles in DNA binding and the subsequent regulation of gene transcription, controlling Ophiocordyceps sinensis sexual reproduction. Alternative splicing, differential occurrence and transcription of the MAT1-1-1 and MAT1-2-1 genes have been demonstrated in Hirsutella sinensis (GC-biased Genotype #1 of the 17 O. sinensis genotypes), suggesting self-sterility under heterothallic or hybrid outcrossing. In this study, the MATαHMGbox domains of MAT1-1-1 proteins in wild-type Cordyceps sinensis isolates were shown to cluster into 5 clades in the Bayesian clustering tree and belong to diverse stereostructure morphs under 19 AlphaFold codes. The HMG-boxROX1-like domains of MAT1-2-1 proteins, on the other hand, were shown to cluster into 2 branched Bayesian clades and belong to stereostructure morphs under 25 AlphaFold codes. Correlation analysis revealed that 1–3 amino acid substitutions in the DNA-binding domains of the mating proteins resulted in altered hydrophobicity and secondary and tertiary structures of the DNA-binding domains of the proteins, especially altered stereostructures of the hydrophobic cores formed by 3 critical α- helices within the functional domains of the proteins. Fungal origin analysis revealed possible heterospecific fungal sources of mating proteins with stereostructure variations in wild-type C. sinensis isolates, suggesting that alterations in DNA binding function and the subsequent regulation of mating-related gene transcription are involved in ensuring the accuracy and genetic diversity of heterothallic and hybrid reproduction of O. sinensis during the lifecycle of the C. sinensis insect–fungal complex.
Li et al. (Mon,) studied this question.