天然冬虫夏草有性生殖过程中交配基因的差异表达和生殖模式的探讨

Differential transcription of mating-type genes during sexual reproduction of natural Cordyceps sinensis

天然冬虫夏草为冬虫夏草菌侵染蝙蝠蛾幼虫后形成的虫菌复合体,从中检出17种基因型冬虫夏草菌和多种真菌。该文综述天然冬虫夏草、中国被毛孢(GC偏倚基因型#1冬虫夏草菌)的交配基因及其转录,探讨其交配模式。冬虫夏草宏基因组和宏转录组中含有特异交配型MAT1-1和MAT1-2的交配基因和转录子,因其菌物来源不详,无法准确推测其交配模式。该文揭示237株中国被毛孢菌株的交配基因差异性存在,构成基因水平的有性生殖调控。中国被毛孢转录水平的有性生殖调控包括:交配基因差异性转录沉寂;交配基因MAT1-2-1转录子含未剪切的内含子Ⅰ,内含终止密码。中国被毛孢L0106和1229号菌株交配基因互补性差异转录,不支持(假)同宗配合的自交;但可产生互补的交配蛋白,完成异宗配合。冬虫夏草子座、子囊果和子囊孢子中检出多种AT偏倚基因型菌,具有基因组独立性,能否成为中国被毛孢的交配伴侣、完成有性生殖有待证实。蝙蝠蛾拟青霉FENG号菌株的交配基因差异性转录,与中国被毛孢L0106号菌株形成互补,能否突破生殖隔离完成杂交有待证实。基因型#13~14冬虫夏草菌呈现2种亲代真菌的大片段DNA交叉互换和遗传物质重组,可能代表杂交或准性生殖的子代变异菌。冬虫夏草菌交配基因的差异性存在和表达,为人工培殖冬虫夏草、解决日益匮乏的天然资源提供了生殖生理学的关键科学信息。

The Chinese Pharmacopeia defines natural Cordyceps sinensis as an insect-fungal complex,which is developed after Ophiocordyceps sinensis infects a larva of Hepialidae family.Seventeen genotypes of O.sinensis have been identified in natural C.sinensis,which are genome-independent and exhibit“Hirsutella sinensis-like”morphologic and growth characteristics,in addition to>90 co-colonized fungal species in natural Cordyceps sinensis spanning at least 37 fungal genera.This paper summarized the literature reports and GenBank database regarding occurrence and transcription of the mating-type genes of MAT1-1 and MAT1-2 idiomorphs in natural Cordyceps sinensis,in H.sinensis(GC-biased Genotype#1 of O.sinensis)and Samsoniella hepiali(Paecilomyces hepiali),to infer the mating pattern of O.sinensis in the lifecycle of natural C.sinensis.The mating-type genes and transcripts of MAT1-1 and MAT1-2 idiomorphs were identified in the metagenomes and metatranscriptomes of natural C.sinensis.However,their fungal sources are unclear because of cocolonization of several genotypes of O.sinensis and multiple fungal species in natural C.sinensis.The mating-type genes of MAT1-1 and MAT1-2 idiomorphs were differentially present in 237 H.sinensis strains,constituting the genetic control of the O.sinensis reproduction.Transcriptional control of the O.sinensis reproduction includes①differential transcription or silencing of the mating-type genes of MAT1-1 and MAT1-2 idiomorphs,and②the MAT1-2-1 transcript with unspliced intron I that contains 3 stop codons.Research on the H.sinensis transcriptome demonstrated differential and complementary transcriptions of the mating-type genes of MAT1-1 and MAT1-2 idiomorphs in Strains L0106 and 1229,which may become mating partners to accomplish physiological heterothallism.The differential occurrence and transcription of the mating-type genes in H.sinensis are inconsistent with the self-fertilization hypothesis under homothallism or pseudohomothallism,but instead indicate the need of mating partners of the same H.sinensis species,either monoecious or dioecious,for physiological heterothallism,or heterospecific species for hybridization.Multiple GC-and AT-biased genotypes of O.sinensis were identified in the stroma,stromal fertile portion(densely covered with numerous ascocarps)and ascospores of natural C.sinensis.It needs to be further explored if the genome-independent O.sinensis genotypes could become mating partners to accomplish sexual reproduction.S.hepiali Strain FENG experienced differential transcription of the mating-type genes with a pattern complementary to that of H.sinensis Strain L0106.Additional evidence is needed to explore a hybridization possibility between S.hepiali and H.sinensis,whether they are able to break the interspecific reproductive isolation in order to adapt the extremely harsh plateau ecological environment.Genotypes#13~14 of O.sinensis feature large DNA segment reciprocal substitutions and genetic material recombination between 2 heterospecific parental fungi,H.sinensis and an AB067719-type fungus,indicating a possibility of hybridization or parasexuality.Our analysis provides important information at the genetic and transcriptional levels regarding the mating-type gene expression and reproduction physiology of O.sinensis in the sexual life of natural C.sinensis and offers crucial reproductive physiology evidence,to assist in the design of the artificial cultivation of C.sinensis to supplement the increasing scarcity of natural resource.