Transcriptomic Analysis Of Ji Ao Tilapia In Response To Streptococcus Agalactiae Stress Under High Temperature

Gi Ao tilapia is a new species hybrid of NEW GIFT O.niloticus?×O.aureus?and with its advantages of high male rate,fast growth rate and high resistance of cold,pathogen and hypoxia.However,Streptococcus agalactiae infection frequently in hot seasons has become a crucial factor restricting the sustainable development of tilapia industry.Therefore,to reveal the immune response mechanism of Ji Ao tilapia following S.agalactiae infection in high temperature is an urgent factor to expand the breeding scale.In this study,Ji Ao tilapia following S.agalactiae infection in high temperature(32?)and analysis the immune response mechanism of gill.The type of pathogen and the environment of the host will influences the genes differentially expressed,different stages of infection also influence the genes type and quantity.We analyzed the Transcriptome of initial infection period(B6h),dying period(B9h),inflection point(B15h)and plateau period(B18h).In addition,microscopic observations of pathological sections corresponding to the infection stage were performed.The microscopic observation and analysis of the pathological section revealed that there was no significant differential in the four infection period except the dying stage(B9h).A total of 8759 differentially expressed genes were obtained in the transcriptome,including 3846 up-regulated and 4313 down-regulated.The number of down-regulated genes related to immunity was much greater than the up-regulated.In the GO enrichment analysis found that the immune response and innate immunity in the initial infection period(B6h / P6h),dying period(B9h / P9h),inflection point(B15h / P15h)and plateau period(B18h / P18h)were significantly down-regulated,indicating that the host's immune function was suppressed during the four infection stages.Cytokine signaling pathways,cell adhesion,antigen processing and presentation are significantly up-regulated and enriched in the initial stage of infection,indicating that humoral immunity plays an important role in the initial stage of infection.Among them,the downregulation of the immune response to bacteria and the presentation of antigens through the major histocompatibility complex were significant enriched in the initial stage of infection(B6h)and dying stage(B9h),the defense response and the processing and presentation of antigens were significant enriched in the inflection point(B15h)and plateau(B18h).Through KEGG pathway enrichment analysis found the phagosome and cell adhesion molecules significantly enriched in the four infection stages,while in the dying stage,inflection point and plateau stage were significantly enriched with Intestinal immune network for ig A production and cytokine-cytokine receptor interaction.It is worth noting that Toll-like receptor signaling pathway and Cytosolic DNA-sensing pathway recovered to a very significant enrichment in the plateau period.The differential expression analysis of the transcriptome of the four periods of tilapia infection revealed that:(1)The immune regulation mechanism is different in different infection periods and the same immune regulation pathway also change in up and down regulation at different periods.(2)Tilapia at the inflection point and plateau stage were the fish that survived,and their defense response and innate immune response were significantly down-regulated.In the analysis of KEGG pathway,Toll-like receptor signaling pathway was found significantly enriched in the plateau stage,indicating that cellular immunity may be involved in the plateau stage immune response.(3)The total expression of genes in the four stages of infection was only 7.5%,indicating that the gene expression types of the four infection periods were quite different.(4)Through gene node and function analysis of the gene network diagram,1L-1beta,vcam1,RAB7 A and cd226 plays an important role in the immune process.