Soapberry (Sapindus mukorossi Gaertn.) is a tree species of the family Sapindaceae, the pericarp of which is rich in triterpenoid saponins, which are important in chemical production, biomedicine, and other fields. Cytochrome P450 monooxygenase (CYP450) is involved in the modification of the skeletons of triterpenoid saponins and is linked to their diversity. We previously identified 323 CYP450 genes in the transcriptome of soapberry and screened 40 CYP450 genes related to the synthesis of triterpenoid saponins by gene annotation and conserved structural domain analysis. The genetic structure and phylogeny of the CYP450 genes were analyzed separately. Phylogenetic analysis categorized the CYP450 genes of soapberry into five subfamilies, the members of which had similar conserved cumulative sequences and intron structures. A cis-acting element analysis implicated several genes in the responses to environmental changes and hormones. The expression of several genes during eight periods of fruit development was analyzed by real-time quantitative qRT-PCR; most showed high expression during the first four periods of fruit development, and their expression decreased as the fruits matured. A co-expression network analysis of SmCYP450s and related genes in the triterpenoid saponin synthesis pathway was performed. Correlation analysis showed that 40 SmCYP450s may be involved in saponin synthesis in soapberry. The triterpenoid saponin synthesis-related candidate genes identified in this study provide insight into the synthesis and regulation of triterpenoid saponins in soapberry.

Genome-Wide Identification, Characterization, and Expression Analysis of the CYP450 Family Associated with Triterpenoid Saponin in Soapberry (Sapindus mukorossi Gaertn.)