Triterpenes are natural products of plants that can defend against microorganisms and various stresses. Oxidosqualene cyclase (OSC), the key rate-limiting enzyme of the triterpene biosynthetic pathway, catalyzes 2,3-oxidosqualene into sterols and triterpenes with different skeletons through the chair–boat–chair (CBC) conformation or chair–chair–chair (CCC) conformation. They were expanded in plants mainly by tandem duplication and are distributed in many plant lineages. They have multiple biological activities, including as functional foods and drugs. Here, we summarize the current characterized forest OSCs and their potential functions, especially for pharmacological applications. The study of triterpene-catalyzed enzyme OSC has an important scientific role and potential economic value. This paper summarizes the research advances of the main members of the OSC family in plants, their structure and function, the biosynthesis of triterpenes, and the molecular evolution of OSC.

The oxidosqualene cyclase family of Rosa rugosa (RrOSC) provides a starting point for the triterpenoid pathway, which contributes to the medicinal value of the extraction of tissues of Rosa rugosa. However, the structure and function of key RrOSCs of active triterpenoids remain ambiguous. In this study, a total of 18 RrOSC members with conservative gene structures and motifs were identified based on the genome of Rosa rugosa. The RrOSCs were located on three chromosomes including two gene clusters that derived from gene replication. The phylogenetic relationship divided RrOSCs into six groups, and the RrOSCs of GI and GIV that were represented by lupeol or α-amyrin were identified as likely to include candidate genes for producing active triterpenoids. Considering the high expression or specific-tissue expression of the candidates, RrOSC1, RrOSC10, RrOSC12, and RrOSC18 were considered the key genes. RrOSC12 was identified in vitro as lupeol synthase. The results provided fundamental information and candidate genes for further illustration of the triterpenoid pathway involved in the pharmacological activities of Rosa rugosa.

Rosa rugosa is highly regarded for its aesthetic and therapeutic qualities. In particular, R. rugosa’s flowers are known to produce essential oils containing a mixture of volatile terpenes, phenylpropanoids, and other compounds. Despite this, extensive research exists on volatile terpenes in flowers, while the knowledge of non-volatile terpenes in distinct tissues is still limited. Using UPLC–ESI–MS/MS, a comprehensive analysis of the terpene metabolites in five different tissues of R. rugosa was conducted. These metabolites accumulated in distinct tissues, and the majority of them were triterpenoids. Transcriptome data were collected from five tissues using RNA-seq. Transcriptomics and metabolomics were utilized to evaluate the triterpene biosynthesis pathway, resulting in new insights into its regulation and biosynthesis. The RrOSC10 was identified as a key enzyme in converting 2,3-oxidosqualene into α-amyrin, potentially contributing to the triterpene biosynthesis pathway. Furthermore, the expression of the RrOSC10 gene was upregulated by salinity for 0.5 h and 1 h, with subsequent downregulation at 2 h. This study lays a foundation for future research on the biosynthesis and accumulation of triterpenes in R. rugosa.

The flower is the main organ that produces essential oils in many plants. The yield of raw flowers and the number of secretory epidermal cells are the main factors for essential oil production. The cultivated rose species “Pingyin 1” in China was used to study the effect of RrANT1 on floral organ development. Eighteen AP2 transcription factors with dual AP2 domains were identified from Rosa rugosa genome. RrANT1 belonged to euANT. The subcellular localization results showed that RrANT1 protein is localized in the nucleus. The relative expression level of RrANT1 in the receptacle is higher than that in petals in the developmental stages, and both decreased from the initial phase to senescence. Compared with the RrANT1 expression level in petals in the blooming stage, RrANT1 expression level was significant in petals (~48.8) and highest in the receptacle (~102.5) in the large bud stage. It was only highly expressed in the receptacle (~39.4) in the blooming period. RrANT1 overexpression significantly increased petunia flower and leaf sizes (~1.2), as well as flower fresh weight (~30%). The total number of epidermis cells in the petals of overexpressing plants significantly increased (>40%). This study concluded that RrANT1 overexpression can increase the size and weight of flowers by promoting cell proliferation, providing a basis for creating new rose germplasm to increase rose and essential oil yield.