Study On Whole Genome Sequencing And Hypoxic Stress Response Of Mactra Veneriformis

In this study,Mactra veneriformis was studied by whole genome sequencing,survival under hypoxia stress,activities of antioxidant indexes and respiratory related enzymes,and transcriptomic analysis.For the initial occasion,complete the whole genome sequencing of M.veneriformis.The response mechanism of M.veneriformis under hypoxia stress was explored from the physiological and biochemical levels as well as molecular biological levels.This provides reference materials for further exploring the mechanism of low oxygen tolerance and creating new germplasm for low oxygen tolerance in M.veneriformis.The results are as follows:1.Illumina sequencing,Pacific Biosciences sequencing and High-throughput chromosome conformation capture were used to assemble high quality chromosome level genomes.M.veneriformis had a genome size of 926.72 Mb in size,with 916.5 Mb of sequence mapped to 19 chromosomes,wherein Contig N50 was 6.44 Mb and Scaffold N50 was 48.06 Mb.The genome contains a repetitive sequence of 345.41 Mb,accounting for approximately 37.27% of the entire genome of the four horned clam.M.veneriformis contains28446 coding genes,and 90.59% of the genes can be functionally annotated,indicating a high quality of genome assembly.2.12,239 single-copy orthologs,3,130 multiple-copy orthologs,and 765 unique gene were identified in M.veneriformis genome.The divergence time with fellow Veneroida Cyclina sinensis and Mercenaria mercenaria is the most recent,277.02 Mya.114 and 4 gene families showed expansion and contraction,respectively.A total of 88 positive selection genes were identified.3.Studies on the survival of M.veneriformis under hypoxia stress,the activities of antioxidant indexes and respiratory related enzymes found that the survival rate of M.veneriformis decreased with the decrease of dissolved oxygen concentration under the same hypoxia stress time.Under the same low oxygen concentration,the longer the stress time,the higher the mortality rate and the lower the survival rate.Stress time and dissolved oxygen concentration had significant effects on enzyme activity.Hypoxia stress on the activities of superoxide dismutase,catalase,pyruvate kinase,lactate dehydrogenase and malondialdehyde content in M.veneriformis gill and hepatopancreas initially increased and then decreased,and there were significant differences in the activities between the control group and the hypoxia group(P < 0.05).4.Transcriptome sequencing was performed on M.veneriformis branchial filament tissues under normal and hypoxia conditions by high-throughput sequencing technology,and54.58 Gb of clean data were obtained.There were differences in gene expression between the normal-oxygen group and the hypoxia group.Control group A and hypoxia group B had the most differentially expressed genes(7473 genes),among which 4000 up-regulated genes and3473 down-regulated genes.Secondly,there were 6407 differentially expressed genes between hypoxia group B and hypoxia group C,with 3535 up-regulated genes and 2872down-regulated genes.There were 5581 differentially expressed genes in the control group A and the hypoxia group C,2676 up-regulated genes and 2905 down-regulated genes.According to the enrichment of GO functional annotations,differential genes were mainly concentrated in the membrane of cell components,metabolism in biological processes and binding of molecular functions.The enrichment of KEGG pathway showed that multiple metabolic and genetic information processing pathways were activated.