Abstract Background Soapberry ( Sapindus mukorossi ) is an economically important multifunctional tree species. Triterpenoid saponins have many functions in soapberry. However, the types of uridine diphosphate (UDP) glucosyltransferases (UGTs) involved in the synthesis of triterpenoid saponins in soapberry have not been clarified. Results In this study, 42 SmUGT s were identified in soapberry, which were unevenly distributed on 12 chromosomes and had sequence lengths of 450 bp to 1638 bp, with an average of 1388 bp. The number of amino acids in SmUGTs was 149 to 545, with an average of 462. Most SmUGTs were acidic and hydrophilic unstable proteins, and their secondary structures were mainly α-helices and random coils. All had conserved UDPGT and PSPG-box domains. Phylogenetic analysis divided them into four subclasses, which glycosylated different carbon atoms. Prediction of cis- acting elements suggested roles of SmUGT s in plant development and responses to environmental stresses. The expression patterns of SmUGT s differed according to the developmental stage of fruits, as determined by transcriptomics and RT-qPCR. Co-expression network analysis of SmUGT s and related genes/transcription factors in the triterpenoid saponin synthesis pathway was also performed. The results indicated potential roles for many transcription factors, such as SmERF s, SmGATA s and SmMYB s. A correlation analysis showed that 42 SmUGT s were crucial in saponin synthesis in soapberry. Conclusions Our findings suggest optimal targets for manipulating glycosylation in soapberry triterpenoid saponin biosynthesis; they also provide a theoretical foundation for further evaluation of the functions of SmUGT s and analyses of their biosynthetic mechanisms.

Identification and analysis of UGT genes associated with triterpenoid saponin in soapberry (Sapindus mukorossi Gaertn.)