Transcriptomics And Metabolomics Of Meat Quality Traits In Three Sheep Breeds

Meat quality traits are economically important traits in sheep and are closely related to meat production levels and economic efficiency.As a complex quantitative trait,the phenotypic differences caused by it are genetically regulated by both master and micro-effective polygenes.Therefore,obtaining candidate genes related to meat quality traits has become one of the priorities for genetic improvement of livestock and poultry.For this reason,this study was conducted to compare the meat performance and meat quality indexes of Dorper sheep,Tan sheep and Small-tailed Han sheep（8 each）,while transcriptomic and metabolomic techniques（3 each）were used to investigate the changes of metabolites and gene expression regulation in the muscle tissue of different breeds of sheep,in order to initially reveal the intrinsic connection between the two,so as to better understand the molecular regulation mechanism of sheep meat quality trait formation.The main findings are as follows.1.The live weight,carcass weight,net meat weight and protein content of the longest dorsal muscle of Dorper sheep were significantly higher than those of Tan sheep and Small-tailed Han sheep（P<0.05）,the muscle fiber density and inosinic acid content were significantly lower than those of Tan sheep and Small-tailed Han sheep（P<0.05）,the pH24h,muscle fiber diameter,inosine content,alcohol and ester content were significantly higher than those of Tan sheep（P<0.05）,and the total amino acid content was significantly higher than that of Small-tailed Han sheep（P<0.05）.The fat and selenium content of the longest dorsal muscle of Tan sheep were significantly higher than those in Dorper sheep and Small-tailed Han sheep,and the L*value of meat color and hydrocarbon content were significantly higher than those in Dorper sheep.The water loss rate,shear force and pH24h of the longest dorsal muscle of Small-tailed Han sheep were significantly higher than those of Dorper sheep and Tan sheep（P<0.05）,the back fat thickness,meat color b*value and total fatty acid content were significantly lower than those of Dorper sheep and Tan sheep（P<0.05）,the aldehyde content was significantly higher than that of Tan sheep（P<0.05）,and the GR value was significantly lower than that of Dorper sheep（P<0.05）.2.A total of 820 and 237 differentially expressed mRNAs and lncRNAs were obtained by transcriptomics,of which 99 and 82,436 and 105,552 and 129 differentially expressed mRNAs and lncRNAs were obtained between the Dorper sheep and Tan sheep,Small-tailed Han sheep and Dorper sheep and Small-tailed Han sheep and Tan sheep groups.GO enrichment analysis showed that differentially expressed mRNAs were significantly enriched in 224,517 and 657 GO entries,while differentially expressed lncRNA target genes were significantly enriched in 474,832 and 740 GO entries between the groups.KEGG pathway enrichment results showed that differentially expressed mRNAs between groups were enriched in 121,197 and 206 metabolic pathways,including cAMP,TGF-β,MAPK,AMPK,purine metabolism,glycerophospholipid metabolism,amino acid and fatty acid metabolism and glycolysis/xenobiotic signalling pathways related to muscle development and lipid metabolism;and the target genes of differentially expressed lncRNAs were enriched in 242,258 and 268 pathways,mainly involved in glutathione metabolism,regulation of adipocyte lipolysis,citric acid cycle（TCA cycle）,cytokine receptor interactions,cAMP signalling pathway and other metabolic pathways related to muscle development and meat quality regulation.Therefore,FOS,PPARGC1A,FABP4,LPIN1,CS,AMPD1,AMPD3,NT5C1A,GPI,PFKm,PKMand TCONS₀0088027,TCONS₀0172842,TCONS₀0129197,TCONS₀0188653 were further screened for candidate genes and regulators that may be associated with meat quality traits in sheep.3.A total of 278 differential metabolites were obtained by metabolomics techniques,including 143,151 and 94 between the Dorper sheep and Tan sheep,Small-tailed Han sheep and Dorper sheep and Smalltailed Han sheep and Tan sheep groups.KEGG pathway showed that the differential metabolites were enriched into 60,69 and 52 metabolic pathways.The combined KEGG pathway analysis of differential metabolites and differentially expressed genes showed that there were 49 co-enriched pathways,including 12 pathways related to meat quality regulation and flavour substance metabolism,including phosphatidylinositol signalling system,phosphatidylinositol metabolism,glycerophospholipid metabolism,glycerol ester metabolism,purine metabolism,etc.A total of 43 differentially expressed genes and 94 differential metabolites were enriched in these 12 Among them,the differentially expressed genes AMPD1,CS,IDH3A,ETNPPL,AKR1B1,DGKE,LPIN1 and ABCA1 were correlated with the differential metabolites xanthine,isocitric acid,phosphatidylcholine,phosphatidylethanolamine,triglyceride and diglyceride.In summary,there are some breed differences in meat performance and meat quality among Dorper sheep,Tan sheep and Small-tailed Han sheep.Some of the differentially expressed genes screened in this study can be used as key candidate genes for meat quality traits in sheep,providing a theoretical basis for breed selection and improvement of sheep and breeding of new Ningxia quality meat sheep breeds.