Identification and genome organization of saponin pathway genes from a wild crucifer, and their use for transient production of saponins in Nicotiana benthamiana. (November 2015)

• Record Type: Journal Article
• Authors: Khakimov, Bekzod; Kuzina, Vera; Erthmann, Pernille Ø.; Fukushima, Ery Odette; Augustin, Jörg M.; Olsen, Carl Erik; Scholtalbers, Jelle; Volpin, Hanne; Andersen, Sven Bode; Hauser, Thure P.; Muranaka, Toshiya; Bak, Søren
• Is Part Of: Plant journal. Volume 84:Number 3(2015:Nov.)
• Page Start: 478
• Page End: 490
• Publication Date: 2015-11
• Subjects: Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.13012
• Languages: English
• ISSNs: 0960-7412

Abstract

<abstract abstract-type="main" id="tpj13012-abs-0001"> <title>Summary</title> <p>The ability to evolve novel metabolites has been instrumental for the defence of plants against antagonists. A few species in the <italic>Barbarea</italic> genus are the only crucifers known to produce saponins, some of which make plants resistant to specialist herbivores, like <italic>Plutella xylostella</italic>, the diamondback moth. Genetic mapping in <italic>Barbarea vulgaris</italic> revealed that genes for saponin biosynthesis are not clustered but are located in different linkage groups. Using co‐location with quantitative trait loci (QTLs) for resistance, transcriptome and genome sequences, we identified two 2, 3‐oxidosqualene cyclases that form the major triterpenoid backbones. LUP2 mainly produces lupeol, and is preferentially expressed in insect‐susceptible <italic>B. vulgaris</italic> plants, whereas LUP5 produces β‐amyrin and α‐amyrin, and is preferentially expressed in resistant plants; β‐amyrin is the backbone for the resistance‐conferring saponins in <italic>Barbarea</italic>. Two loci for cytochromes P450, predicted to add functional groups to the saponin backbone, were identified: CYP72As co‐localized with insect resistance, whereas CYP716As did not. When <italic>B. vulgaris</italic> sapogenin biosynthesis genes were transiently expressed by CPMV‐HT technology in <italic>Nicotiana benthamiana</italic>, high levels of hydroxylated and carboxylated triterpenoid structures accumulated, including oleanolic acid, which is a precursor of the major resistance‐conferring saponins. When the <italic>B. vulgaris</italic> gene for sapogenin 3‐<italic>O</italic>‐glucosylation was co‐expressed, the insect deterrent 3‐<italic>O</italic>‐oleanolic acid monoglucoside accumulated, as well as triterpene structures with up to six hexoses, demonstrating that <italic>N. benthamiana</italic> further decorates the monoglucosides. We argue that saponin biosynthesis in the <italic>Barbarea</italic> genus evolved by a neofunctionalized glucosyl transferase, whereas the difference between resistant and susceptible <italic>B. vulgaris</italic> chemotypes evolved by different expression of oxidosqualene cyclases (OSCs).</p> </abstract>