Preliminary Study On Genetic Differentiation And Inheritance Stability Of Mitochondrial Genomes In Cordyceps Militaris

Cordyceps militaris is an edible and medicinal fungus used for developing health food.They are often used as an alternative to Ophiocordyceps sinensis for clinical treatment because of their similar chemical composition and biological activity substances.Compared with the abundant market demand,the resoure of wild C.militaris is insufficient.Artificial cultivation of C.militaris is the appropriate way to solve this problem.However,the degeneration phenomenon of C.militaris during artificial cultivation is the restrictive bottleneck of the industrial exploitation.How to solve this problem has become the focus of many researches.Genetic mutations are the dominant factors of strain degeneration,so it is significance to study the C.militaris' genetic mechanisms.Studies have shown that mitochondrium has an independent genetic system and the evolution rate of mitochondrial genomes is greater than that of nucleus genes in the process of evolution.This topic focused on the C.militaris mitochondrial genomes research to provide a possible new idea of solving the problem of strain degradation.We analyzed nucleotide variability in mitochondrial genomes and nucleus genes of 10 C.militaris strains,and compared the evoutionary relationships between mitochondrial and nuclear genes.The alignment of 10 C.militaris mitochondrial genomes generates 34,067 positions.There are 127 pleomorphic positions at exonic regions of the standard protein-coding genes and the tRNA,rRNA regions,and 44 pleomorphic loci at intronic regions.On the whole,the variability is similar between exonic and intronic regions.There are 125 pleomorphic positions at intergenic regions.The variability at intergenic regions is higher than that at genic regions.The alignment of 10 C.militaris nucleus genes generates 9,822 positions which include 105 pleomorphic loci.Nucleotide variability frequencies of nuclear genes is 1.0%,while it is approximate 0.6% at mitochondrial genomes.The result shows that variability frequencies of nucleus genes is a little higher than that ofmitochondrial genomes.Due to lack of time,there is no comprehensive statistics of more nuclear genes.And we need more evidences to verify our conclusion.The evoutionary relationships between mitochondrial genomes and nuclear genes are basically consistent.Studies showed that C.militaris mitochondrial genomes contain 8variable introns(rnl-i1-i4,cob-i1,cox1-i1,cox2-i1,and cox3-i1).In order to establish a system of rapid-detecting C.militaris mitochondrial genetypes,we regarded those introns as markers,and designed specific primer pairs that was used for detecting if them were exist.The established system works on testingmitochondrial genetypes of different C.militaris strains.In order to explore the relationship between strain degradation and C.militaris mitochondrial genetypes,we separated 25 single spore strains of 3 C.militaris and tested their mating types.Eight single spore strains and 10 parent strains were used for subculturing.We treated 8 days as one cycle.During the period of continuous subculturing,degeneration phenomnons were observed.C.militaris mitochondrial genetypes were tested every 5generations.We subcultured 15 generations and separated 2 areas of degradation,then tested their mitochondrial genetypes.Unexpectedly,there is no difference with original strains in mitochondrial genetypes.However,in the current study,too few generations have been carried out to determine whether it had a direct relationship between the strain degradation and the change of C.militaris mitochondrial genetypes.This is also one of the important research subjects of our next works.