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Characterization of a 2,3‐oxidosqualene cyclase in the toosendanin biosynthetic pathway of Melia toosendan
Author(s) -
Lian Xufan,
Zhang Xiuli,
Wang Fei,
Wang Xiaoning,
Xue Zheyong,
Qi Xiaoquan
Publication year - 2020
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/ppl.13189
Subject(s) - biology , biosynthesis , triterpene , biochemistry , meliaceae , gene , metabolic pathway , lupeol , chemistry , botany , medicine , alternative medicine , pathology
Toosendanin, bearing a furan ring, is a limonoid belonging to the group of tetranortriterpenoids. Toosendanin is a phytochemical found in the medicinal plant Melia toosendan Sieb. et Zucc. of the Meliaceae family. Toosendanin and its derivatives demonstrate high insecticidal activity and are important pesticides derived from plants. Despite intensive investigation of limonoids over several decades, the biosynthetic pathway of these triterpenoids is less understood. To identify the key enzymes involved in the toosendanin biosynthetic pathway, we analyzed the contents of toosendanin in various plant tissues and parts and found that the highest level of toosendanin was found in the developing fruit and gradually decreased as the fruit matured. More than 346 116 transcripts were assembled based on 394 million paired‐end Illumina reads and 6 million PacBio reads from the pooled RNA samples of fruits, leaves and young barks. A total of 186 263 genes were predicted. Six 2,3‐oxidosqualene cyclase (OSC) genes were identified by analyzing the association between gene expression and metabolite profiles. Functional analyses using the Nicotiana benthamiana transient expression assay showed that MtOSC1 catalyzed 2,3‐oxidosqualene to produce a tetracyclic triterpene skeleton, tirucalla‐7,24‐dien‐3β‐ol, which is predicted as the precursor for toosendanin biosynthesis. We identified another OSC, MtOSC6, which is a lupeol synthase. Using synthetic biology methods, these identified enzymes could be used to model a biosynthetic pathway to produce large quantities of toosendanin.