The Genetic Diversity And Evolution Of Five Nematode-trapping Fungi Based On Mitochondrial Genome

Nematode-trapping fungi are anamorphic state of Ascomycota,Orbiliaceae,Orbilia,which vegetative hyphae may be specialized various capturing device(abbreviate to device)to capture nematodes.The main four devices are adhesive network,adhesive knobs(sometimes with non-contracting ring),adhesive columns and contracting rings.There are some hypothesis about the evolution of device,and some people have researched this topic in the level of combining multi-genes or nuclear genome.However,the mitochondrial genomes have not be used to study the evolution of device,and the diversity of mitochondrial genomes of fungi with various device has not carried.In this study,five strains of fungi were selected:Arthrobotrys musiformis YMF1.03753,which produces the three-dimensional network;Dactylellina leptospora YMF1.00042,which produces a sticky ball and a non-shrinking ring;Dactylellina cionopagum YMF 1.00569,which produces the sticky column;Dactylella tenuis YMF 1.00469,which produces contractile ring,and Dactylella tenuis YMF 1.00469,which has a close relationship with the other four strains but don't produce trap.We got the mitochondrial genome of the five strains sequenced and filled the gap,then annotated the mitochondrial genome and got physical mapping.The mitochondrial genome diversity of nematode-trapping fungi was compared and analyzed,and evolution of the trap was revealed from the mitochondrial genome level.The main results of the paper are as follows:1.The mitochondrial genome size of the five fungi is between 184443-280699 bp,with A.musiformis being the smallest and Dre.brochopaga being the largest;Dre.brochopaga has the longest intron length(185386 bp)with the number of 68 introns,while only 50 of A.musiformis,intron length drive the significant size expansion of mitogenomes.In the order of protein-coding genes,except for the position of the atp8 gene of Dactylella tenuis,the order of the protein coding genes of the other four species is highly consistent,clockwise:cox1,atp6,nad2,nad3,cox3,cob,nad4L,nad5,nad6,cox2,atp8,nad4,atp9,nad1.The tRNA genes of the five fungi have common insertion sites:coxl-rps3,nad3-cox3,nad4-atp9,rns-rnl,rnl-nad1 and nadl-coxl,but showed a difference in the number of tRNA genes.Among the five fungi,except for A.musiformis,the nad4L overlaps with the nad5,and the overlapping sequence of Dac.cionopaga and Dac.leplospora is ATGTACTTATTAA,Dactylella tenuis and Dre.brochopaga is A.2.The atp9,cob,cox I,nad5,nad2 protein-coding genes of Dre.brochopaga producing a contractile loop are significantly different from those of the other four strains.Both atp9 and cob have 14 and 10 amino acid deletions in one region,and 7 and 20 amino acid deletions in coxl at two sites,respectively.nad5 also has 49 and 5 amino acid deletions at two sites,respectively.And there are 16 amino acid insertion in nad2.In order to verify whether the difference is related to the type of trap,these genes were compared in more strains with different traps.Only the difference in the coding sequence of the nad2 gene was found to be due to the difference in the trap.We suggested that this gene is involved in the need of more energy for the instantaneous expansion of the cell when the contractile loop catches the nematode.3.Combined with 14 protein-coding genes,the phylogenetic analysis of 33 fungi in Ascomycota showed that the Orbiliaceae were aggregated into one clade,and Dactylella tenuis,which did not produce a trap,was located at the base.The first divergence branch was Dre.brochopaga,followed by Dactylellina cionopagum,which produces a sticky column,next the Arthrobotrys musiformis,which produces a three-dimensional network,and then Dactylellina leplo.spora,which produces a sticky ball,is located at the very end and appears at the latest in the evolution of the trap.The results of this analysis are basically consistent with the results obtained from the nuclear genome,indicating that the mitochondrial genome and nuclear genome are co-evolving during the evolution of the trap.4.By analyzing the number of introns of the five fungi,we found that five strains had the same number of introns in nad4L,atp8,nad3,nad6,nad4 and rps3,and there showed a difference in the number of introns of A.musiformis in nad2,Dac.Leplospora in cox2,Dac.Cionopaga in atp9 and Dactylella tenuis in nadl.The number of introns tends to increase as the evolutionary status of adhesive trapping devices increases.In particular,Dactylella tenuis does not contain introns in nadl,and the other four strains have introns in this gene,we suggested that the appearance of the intron is related to the appearance of the trap.Thus,the appearance of introns is closely related to the emergence and evolution of traps.