Metabolome And Transcriptome Association Analysis Of Longissimus Muscle Of Donkeys With High And Low Intramuscular Fat Content

With the improvement of living standards,people are increasingly pursuing excellent meat quality.The meat of donkeys is delicious,rich in protein and high in nutritional value,which has attracted widespread attention from consumers.The content of intramuscular fat(IMF)is closely related to meat quality traits and is one of the important indicators for determining meat quality.China has a long history of raising donkeys,and has a rich variety of local donkeys.However,there are few studies on donkey muscle fat deposition.Literature search includes some research literature from the evolutionary perspective,as well as research on reproduction.The research on meat donkey performance and improving donkey meat quality is basically blank.Therefore,in this experiment,the Guangling donkey was used as the research object.Transcriptome sequencing and metabolome analysis were performed on the Guangling donkey with different intramuscular fat content,and differentially expressed genes were screened.The genetic differences of Guangling donkeys with different intramuscular fat contents were revealed at the molecular level,which provided a theoretical basis for further research on molecular breeding of Guangling donkeys.The main results of this study are as follows:(1)The intramuscular fat content of 10 Guangling donkeys was measured,and divided into two groups according to the level of intramuscular fat content(L,n=3 and H,n=3).The significant differences between H and L groups were found(P<0.0001).RNA-Seq revealed 167 DEGs between H and L groups groups,of which 64 genes were up-regulated and 103 genes were down-regulated.Gene ontology analysis revealed these DEGs(including ITGAL,MAPK,WNT10 B,DLK1,SCD,DGAT2 and CIDEA)were significantly enriched in cell-cell adhesionneutral lipid metabolic process and fat cell differentiation biosynthetic process.Meanwhile,Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed these DEGs were significantly enriched in Arachidonic acid metabolism,HIF-1 signaling pathway and AMPK signaling pathway.In addition,we found that DEGs related to muscle regeneration(DGKA and VEGF)and lipocatabolism(LEPR)were reduced in the high-fat group.Seven differentially expressed genes involved in the above pathways were randomly selected for q PCR verification,and the q PCR results were consistent with the RNA-Seq results(R~2=0.984).(2)UPLC-MS/MS technology was used to analyze the metabolome of the longissimus dorsi muscle of Guangling donkeys with different intramuscular fat contents.The results showed that 591 metabolites were detected in the L and H groups,a total of 72 differentially accumulated metabolites(Fold-Change≥2 or Fold-Changes≤0.5 and VIP≥1),27 were up-regulated,45 These were down-regulated,with lipids(phospholipids,oxidized lipids,and fatty acids),amino acids,organic acids,nucleotides,and carbohydrate metabolites the most.Correlation analysis of metabolomics and transcriptome data showed that there were 35 co-enriched pathways,including glycerophospholipid metabolism,and biosynthesis of unsaturated fatty acids pathways.In terms of biosynthesis of unsaturated fatty acids,polyunsaturated fatty acids(PUFA),including docosahexaenoic acid(DHA)and arachidonic acid(AA)were down-regulated in high-IMF donkeys,while saturated fatty acids(SFA)and monounsaturated fatty acids(MUFA),including eicosanoic acid(20:0)and palmitoleic acid(16:1)was increased.These metabolites are closely related to SCD gene expression.In the glycerophospholipid metabolism pathway,the contents of lysolecithin 16:0,glycerol-3-phosphate(G3P)and lysophosphatidic acid(LPA)are down-regulated in high-IMF donkeys.The results of this study will help to further explore the molecular mechanism of IMF deposition in donkeys in the future,and provide a theoretical basis for the molecular breeding of Guangling donkeys.