Comparative Analysis In Gyrodactylus And Paragyrodactylus Mitochondrial Genomes And Phylogenetic Reconstruction Of Gyrodactylidae

Monogeneans(Platyhelminthes,Monogenea)are parasitic flatworms infected fish,amphibians and reptiles.Monogeneans are the important pathogens for fish,which can often cause severe economic losses.The mitochondrial genome has been widely used in molecular phylogeny and evolution,due to rapid evolutionary rate,conserved products,maternal inheritance and rarely gene recombination.In this study,mitochondrial genomes of Gyrodactylus parvae You,Easy et Cone,2008,Gyrodactylus variegatus sp.nov.,and Paragyrodactylus variegatus You,King,Ye et Cone,2014 were determined and described.A comparative analyses of mitochondrial genomes in Gyrodactylus and Paragyrodactylus were performed.Thereafter,phylogenetic analysis of Gyrodactylidae based on 18s rDNA had been done,and the phylogenetic relationships and the status of Paragyrodactylus among Gyrodactylidae were preliminary investigated as well.Followings are the main results and conclusion:1.The Paragyrodactylus variegatus,Gyrodactylus parvae and Gyrodactylus variegatus mitochondrial genome lengths are 14,517bp,14,702 bp and 14,755 bp,respectively.All the newly sequenced mitochondrial genomes contain 12 proteion-coding,tworRNA,22 tRNA genes and major non-coding regions,which is identical with reported mitochondrial genomes from Monogenea except for major non-coding regions.2.The overall A+T of Paragyrodactylus variegatus,G parvae and G variegatus,are 76.3%,73.5%and 72.0%,respectively.The A + T content value of P.variegatus is higher than that of all reported mitochondrial genomes of monogeneans and the A +T content value of G.parvae and G.variegatus are higher than published Gyrodactylus mitochondrial genomes,especially for the third codon position of PCGs.Three start codons(TTG,GTG and ATG)were found in PCGs of P.variegatus mitochondrial genome,while only one start codon was employed for Gyrodactylus spp.All the three newly mitochondrial genomes used TAA or TAG as the stop codon.3.All 22 tRNA genes can be folded into the common cloverleaf structure except for tRNACys,tRNASer1 and tRNASer2,due to the absence of stable DHU stem.In Gyrodactylus,tRNAIle,tRNAHHis,tRNAPro and tRNAMet have the highest levels of nucleotide conservation,and tRNACys,tRNAGly and tRNAAla show lower level of identical nucleotides.The level of tRNA conservation was not linked to codon usage.4.The first model of rrnL and rrnS secondary structures for Gyrodactylus and Paragyrodactylus were provided.The secondary structures of rrnL and rrnS contain six and three structural domains,respectively.The third domain is absent in rrnL.Domain Ⅲ in rrnS and domains Ⅳ and Ⅴ in rrnL are the most conserved parts5.the gene order between Paragyrodactylus and Gyrodactylus is different:the arrangement of tRNAGln and tRNAMet.Furthermore,Gyrodactylus contains another major noncoding region neighbor on tRNASer2.Comparative analyses of all gene order from Monogenea showed that two conserved gene clusters(tRNAAsn-tRNAPro-tRNAIle-tRNALys and rrnL-tRNACys-rrnS)in monopisthocotyleans which could potentially be a marker used to help define the Polyopisthocotylea and Monopisthocotylea within the Monogenea.6.Gyrodactylus mitochondrial genomes contain two almost identical major non-coding regions,but the similarity of major non-coding regions among different species was not very high.Seven conserved blocks were found in Gyrodactylus major non-coding regions,and Block-G was also found in Paragyrodactylus variegatus major non-coding regions.Paragyrodactylus variegatus mitochondrial genome possess only one major non-coding regions,which include 240 bp repeat sequences and some pertinent elements corresponding to the control region for replication and transcription initiation around Block-G.7.Molecular phylogeny of Gyrodactylidae based on 18s rDNA showed that the viviparous species and oviparous species formed the monophyletic group,respectively.The oviparous group were divided into two branches.Four genus(Scleroductus,leredactylus,Gyrodactyloides and Laminiscus)grouped a small branch.The rest genus formed another clade.Gyrodactylus was proven to be a paraphyletic group.Gyrodactylus clade Ⅰ include two species representing Fundulotrema and Swingleus;Gyrodactylus clade Ⅱ and Paragyrodactylus formed a sister group.