Abstract:We investigated the function of SWEET family genes in the flowering process of tree peony. Based on the ‘Luoyang red’ tree peony petal transcriptome database, the SWEET family genes were identified and analyzed by bioinformatics. The results showed that: (1) a total of 10 SWEET genes with complete open reading frame were obtained. (2) There were little difference in isoelectric point and extinction coefficient of peony SWEET family proteins, among which 5 peony SWEET genes encoded proteins were unstable proteins. Subcellular localization predicted that the 10 SWEET genes of tree peony were located in the cell membrane. Evolutionary tree analysis showed that the SWEET genes of tree peony was more closely related to Arabidopsis thaliana. Structural analysis showed that the structures of tree peony SWEET proteins were very conserved in the evolutionary process. The 10 peony SWEET proteins had 5 identical motiations and all contained two MtN3 saliva domains. (3) The results of soluble sugar content showed that the content of sucrose in tree peony petals decreased continuously, while the contents of fructose and glucose increased continuously, and both reached the peak in the blooming period. (4) Through the analysis of RTqPCR, we found that the expression level of PsSWEET4 at flowering stage was 34 times than that in small bell, and the expression level of PsSWEET8 at flowering stage was 60 times than that in small bells. Combined with the relationship between the expression and evolution of these two genes and the change value of soluble sugar, we presumed that PsSWEET4 and PsSWEET8 might regulate the flowering process indirectly by regulating the transport of fructose and glucose, which layed a foundation for further study of the function of peony SWEET genes in the plant growth and development.