Genetic Parameter Estimation And Response Mechanism Of Marsupenaeus Japonicus Under Nitrite Stress

The Kuruma shrimp Marsupenaeusjaponicus is one of the important aquaculture shrimp species in my country.In recent years,due to the deterioration of the breeding environment,there have been problems such as frequent disease outbreaks and low breeding urvival rates,which has become a constraint on the sustainable and healthy development of the shrimp aquaculture industry.As the main environmental stress factor,nitrite is the main pollutant that is easy to accumulate in the breeding environment.However,there are not many studies on the nitrite tolerance mechanism of M.japonicus in China.This study carried out using the family of M.japonicus.In the nitrite stress experiment,the genetic parameters of nitrite tolerance were estimated,and the response mechanism of M japonicus to nitrite stress was explored at the histological and transcriptomic levels.The results of the study will not only help to analyze the response mechanism of M japonicus to nitrite tolerance,but will also provide important theoretical support for the excavation and genetic breeding of excellent stress-resistant germplasm.The main results of this paper are as follows:1.Estimation of genetic parameters for nitrite tolerance traits of M.japonicusEstimation of genetic parameters is a basic method to understand the genetic characteristics of breeding family traits and the direction of selection.This study is based on the nitrite tolerance test of 12 M japonicus families(100 days old)constructed in 2019 to estimate the genetic parameters of growth traits tolerance and nitrite traits,of which the body length heritability is 0.4956±0.0642,The heritability of body weight is 0.4462±0.0547,which belongs to the high heritability range;the heritability of nitrite tolerance is 0.0930±0.0658,which belongs to the low heritability.The genetic correlation coefficient between body length and body weight of the growth traits of M.was 0.9934±0.0043,and the phenotypic correlation coefficient was 0.9611±0.00 5 8,and both were extremely significant positive correlations(P<0.01).The genetic correlation coefficient between body length and nitrite tolerance traits is 0.0001 ± 0.2733,and the phenotypic correlation coefficient is 0.0676 ± 0.0564;the genetic correlation coefficient between body weight and nitrite tolerance traits is 0.0661 ± 0.2749,and the phenotypic correlation coefficient is 0.0697±0.0564,both were not significantly correlated(P>0.05).Studies have shown that the genetic relationship between nitrite tolerance and growth traits of M.japonicus is not significant.2.Histopathological changes in hepatopancreas of M.japonicus under nitrite stressIn this study,the hepatopancreas tissues of M.japonicus under nitrite stress for 12h and 96h were histopathologically observed.It was found that the hepatopancreas tissue structure of 12h and 96h had obvious damage,and the damage was more obvious after 96h stress than 12h.After 12 hours of nitrite stress,the lumen appeared deformed,the secretory cells swelled,the edges gradually spread,and rupture appeared,causing some of the liver tubules to squeeze;After the gap becomes larger and the secretory cells rupture,part of the cell structure has been ablated and the stellate structure is lost.Studies have shown that nitrite toxicity has caused histopathological damage to the liver and pancreas of M japonicusd,and it is speculated that the vacuolation of M.japonicus is one of the self-defense mechanisms and transport and detoxification mechanisms.3.Transcriptomics study of M japonicus in response to nitrite stressTranscriptome sequencing of the hepatopancreas and gills of M.japonicus under nitrite stress for 12h and 96h were performed to investigate the temporal and spatial expression and stress response at the transcriptome level of M.japonicus under nitrite stress.We obtained 65341 unigenes,their average length is 1127bp and N50 is 1846bp.A comparative analysis of DEGs found that the number of differential genes in hepatopancreas at 96h was more than 12h,and the number of up-regulated genes increased significantly;in gill,compared with 12h,the number of up-regulated genes increased and the number of down-regulated genes decreased in gill.As the stress time increases,the toxic stress effect strengthens,and the related immune response is gradually activated.Studies have shown that there is a severe acute stress response in gill under nitrite stress,and the hepatopancreas,as an organ of immune metabolism,has a richer physiological and biochemical response.GO term analysis and KEGG analysis revealed that nitrite stress activated various immune responses in the gill and hepatopancreas of M japonicus,including interference with the synthesis and metabolism of macromolecules,and the key to inhibiting blood oxygen transport pathways Protein,inhibit redox reactions,inhibit the expression of key genes in detoxification pathways such as liver carboxylesterase and glutathione,which proves that nitrite stress can interfere with the autoimmune system of M.japonicus and increase its susceptibility to pathogens.It is speculated that M.japonicus has its own detoxification mechanism,and reducing its own metabolism is one of its physiological strategies to combat toxicity.4.Temporal and spatial expression analysis of important functional genes of M.japonicus under nitrite stressWe selected 6 important functional genes(MjhsL2,MjhsY,Mjsty,Mjilys,MjCytMnSOD,MjADP-rf)to explore their expression change on different times under nitrite stress(0h,3h,6h,12h,24h,48h,72h,96h)in hepatopancreas,gills and hemolymph of M japonicus.It showed that the six functional genes were significantly down-regulated in gills,comparing with hepatopancreas and hemolymph,the gills was greater down-regulated.It’s speculated that the nitrite stress effect in gills is more direct and severe.The expression level of hemocyanin gene decreased significantly under nitrite stress.In addition,Mjsty,Mjilys,and MjADP-rf all showed significant up-regulation in hepatopancreas,indicating that nitrite stress activated the immune response of shrimp.MjCytMnSOD was significantly down-regulated in the three tissues.It is speculated that prolonged nitrite stress caused oxidative damage to the shrimp and inhibited the expression of antioxidant enzyme genes.