Analysis Of The Composition And Structure Of Mitochondrial Genomes Of 6 Species Of Sarcocystis

Sarcocystis is an intracellular parasitic protozoan with veterinary and public health significance.Mitochondria exist in most eukaryotic cells and have a genome independent of nuclear genes,which is called the mitochondrial genome.At present,the mitochondrial genome has become a common genetic marker for studying the relationship between biological systems.So far,no articles have reported the composition and structure of the mitochondrial genome of Sarcocystis.In this paper,the mitochondrial genomes of Sarcocystis caninum,S.zuoi,S.clethrionomyelaphis,S.eothenomysi,S.cymruensis and S.wenzeli were amplified,sequenced and analyzed by long-segment PCR and other methods.The results are as follows:（1）Part of the mitochondrial genome sequence of S.caninum is 3403 bp in size,including 2 coding genes（COX 1 and CYTB genes）and 5 ribosomal RNA subunit genes（LSUF,LSUG,SSUE,SSUB and LSUA）,and mitochondrial COX1 gene Located upstream of the CYTB gene,the two have the same transcription direction;in addition,the complete mitochondrial COX3 gene sequence of S.caninum was also amplified,but its specific location in the mitochondrial genome is still uncertain.The full length of mitochondrial COX1,CYTB and COX3 genes are 1434 bp,1080 bp and 720 bp,respectively.The mitochondrial COX1 gene uses TCC as the start codon,the mitochondrial CYTB and COX3 genes use ATG as the start codon,and the 3 coding genes stop codons.The sons are TAA.（2）The sequence size of part of the mitochondrial genome of S.zuoi is 3325 bp,containing 2 coding genes（COX1 and CYTB genes）and 3 ribosomal RNA subunit genes（SSUF,LSUD and LSUE）.The mitochondrial COX1 gene is located in the CYTB gene Upstream,both have the same transcription direction.The length,start codon and stop codon of mitochondrial COX1 and CYTB genes are the same as S.caninum.（3）The two partial mitochondrial genome sequences of S.clethrionomyelaphis are 2790 bp（SEQ RZ-1）and 4349 bp（SEQ RZ-3）respectively.SEQ RZ-1 contains 2 coding genes（COX 1 and CYTB genes）.The mitochondrial COX1 gene is located upstream of the CYTB gene,and the transcription direction of the two is the same;SEQ RZ-3 contains the full length of the mitochondrial COX1,COX3 and CYTB genes,and the gene sequence is COX3-CYTB-COX1,the three coding genes have the same transcription direction.No ribosomal RNA subunit gene was identified in SEQ RZ-1 and SEQ RZ-3.S.clethrionomyelaphis full-length COX1 and CYTB genes have the same length and start and stop codons as S.caninum;the full-length mitochondrial COX3 gene is 741 bp in length,and the start and stop codons are TTA and TAA,respectively.（4）The size of partial mitochondrial genome sequences of S.eothenomysi and S.cymruensis are 2810 bp and 2549 bp,respectively.Both of them contain 2 coding genes（COX1 and CYTB genes）and two ribosomal RNA subunit genes（SSUB,and SSUE）.The mitochondrial COX1 gene is located upstream of the CYTB gene,and the two have the same transcription direction.（5）Part of the mitochondrial genome of S.wenzeli is 3752 bp in size,containing 2 coding genes（COX1 and CYTB genes）and 7 ribosomal RNA subunit genes（LSUE,LSUD,SSU9,SSU8,LSU7,LSU15 and SSUB）,The mitochondrial COX1 gene is located upstream of the CYTB gene,and the two have the same transcription direction.Based on sequence alignment analysis,the combination of protein-coding genes（CYTB,COX1 and COX3 genes）in the mitochondrial genome is relatively conserved among different Sarcocystis species,while the flanking sequences of coding genes have large interspecies differences.Sequence analysis and molecular phylogenetic analysis based on the mitochondrial COX1,COX3 and CYTB genes showed that all three coding genes have the ability to be used as molecular marker genes for species identification and phylogenetic analysis of Sarcocystis.The mitochondrial COX3 gene has a greater degree of interspecies discrimination than the COX1 and CYTB genes.