## 3 Results and Discussion
### Effects of Characteristic Bioactive Metabolites on Meat Quality Traits
Seven upregulated DEGs and eight downregulated DEGs played key roles in the differential accumulation of characteris  
Figure 5: Statistical analysis of DEGs. (**A**) Principal component analysis based on overall transcripts. (**B**) Volcano plot of DEGs in the breast muscle of Silkie and Wuding chickens. (**C**) GO enrichment analysis and KEGG pathway enrichment analysis of upregulated genes in Silkie chickens. tic metabolites. _NPR2_ (encoding a natriuretic peptide receptor) and _PDE6B_ (encoding a phosphodieserase) were differentially expressed and were responsible for the significant upregulation of guanine. The downregulation of _PHGDH_ (encoding a phosphoglycerate dehydrogenase) led to the accumulation of glyceric acid. The upregulation of _BHMT2_ (encoding a betaine homocysteine _S_-methyltransferase) promoted _S_-adenosylmethionine synthesis, and the downregulation of _GNMT_ (encoding a glycine _N_-methyltransferase) decreased _S_-adenosylmethionine breakdown. Estrone was activated by the significantly upregulated _HSD17B1_ (encoding a hydroxysteroid 17-beta dehydrogenase) to form estradiol. _UPP2_ (encoding a uridine phosphorylase catalyzing the cleavage of uridine) was downregulated, which led to the accumulation of UMP. _CNDP1_ (encoding a carnosine dipeptidase transforming 4-acetamidobutanoate into homocarnosine) was downregulated, which led to an increase in the 4-acetamidobutanoate content. The significant upregulation of _IL4 II_ promoted the biosynthesis of D-phenyllactic acid. We conducted correlation analysis to identify DEGs that regulate the synthesis of characteristic lipids and fatty acids. A total of 11 lipid metabolism-related DEGs were positively correlated with characteristic lipids and fatty acids (_r_ > 0.4 and \(p\) < 0.05, Figure 7). We identified 11 DEGs that play key roles in the biosynthesis of upregulated characteristic lipids and fatty acids in Silkie chickens. _ADIRF_ promotes adipogenic differentiation. _ABCB1 LA_, _APOD_, and _PRELID3B_ encode proteins that are involved in lipid transport. _ABCB1 LA_ encodes a protein that is capable of transporting PE [62] and is positively correlated with PE, PE(16:0_20:4)-H, PE(18:0_20:4)-H, and PE(36:4)+H. _APOD_ encodes the most abundant and versatile apolipoprotein that facilitates lipid transport and metabolism [63; 64]. _PRELID3B_ encodes a protein that is involved in phospholipid transport [65] and is positively correlated with PE, PG, and CL. The proteins encoded by _ASIP_, _ELOVL2_, _PLPP4_, and _SPTSSBL_ are directly involved in the formation of lipids and fatty acids. _ASIP_ affects the saturation of fatty acids [66] and is positively correlated with PS(C22:5). _ELOVL2_ is directly involved in polyunsaturated fatty acid biosynthesis [67] and is positively correlated with PS(C22:5), PS(C22:6), and PC(C22:6). _PLPP4_ is involved in the synthesis of PE and is positively correlated with PE and PE(16:0_20:4)-H. _SPTSSBL_ encodes a protein that catalyzes the first rate-limiting step in sphingolipid biosynthesis [68] and is positively correlated with ST(m38:0)-H. _ANGPTL6_[69], _RGS16_[70], and _ULK_[71] also play important roles in lipid metabolism. Figure 6: Identification of key DEGs that regulate characteristic metabolic pathways. Orange represents significantly upregulated metabolites and genes in Silkie chickens, and green represents significantly downregulated metabolites and genes.