Effects of a bile acid elicitor, cholic acid, on the biosynthesis of diterpenoid phytoalexins in suspension-cultured rice cells

• Published in: Phytochemistry (Oxford) 2008-02, Vol.69 (4), p.973-981
• Main Authors: Shimizu, Takafumi, Jikumaru, Yusuke, Okada, Atsushi, Okada, Kazunori, Koga, Jinichiro, Umemura, Kenji, Minami, Eiichi, Shibuya, Naoto, Hasegawa, Morifumi, Kodama, Osamu, Nojiri, Hideaki, Yamane, Hisakazu
• Format: Article
• Language: English
• Subjects: bile acids; Bile Acids and Salts - chemistry; Biological and medical sciences; Cell Culture Techniques; cell suspension culture; Chemical constitution; Cholic acid; Cholic Acid - pharmacology; Chromatography, High Pressure Liquid; cultured cells; Diterpene cyclase gene; diterpenoids; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant - drug effects; Gramineae; HPLC–MS/MS; Index Oryza sativa; Metabolism; Metabolism. Physicochemical requirements; Molecular Structure; momilactones; Oryza - cytology; Oryza - genetics; Oryza - metabolism; Oryza sativa; Phytoalexin; phytoalexins; Phytocassane; phytocassanes; Plant physiology and development; Plant Proteins - genetics; Plant Proteins - metabolism; quantitative analysis; rice; Rice suspension cells; Sesquiterpenes; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry; Terpenes - metabolism; Transcription, Genetic - drug effects
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2007.10.005

An HPLC–ESI-MS/MS system was established for the rapid quantification of the major rice phytoalexins, phytocassanes and momilactones. It was shown that cholic acid, an elicitor of rice defense responses, preferentially induced formation of phytocassanes and the transcription of diterpene cyclase genes, including OsCPS2 ( OsCyc2), that are involved in phytocassane biosynthesis in suspension-cultured rice cells. An elicitor of rice defense responses was recently isolated from human feces and was identified as cholic acid (CA). Pathogen infection in rice leaves induces phytocassanes and momilactones, both of which are major diterpenoid phytoalexins in rice, whereas CA mainly induces phytocassanes. We established a high-performance liquid chromatography–electrospray ionization-tandem mass spectrometry protocol for the rapid and accurate quantification of phytocassanes and momilactones. Using this method, we showed that CA preferentially induced the formation of phytocassanes in suspension-cultured rice cells, while a fungal chitin oligosaccharide elicitor induced that of both phytocassanes and momilactones. We further investigated the effects of CA on the expression of diterpene cyclase genes involved in phytoalexin biosynthesis. CA induced the transcription of the genes OsCPS2 ( OsCyc2) and OsKSL7 ( OsDTC1), which are involved in phytocassane biosynthesis, to a greater extent than the genes OsCPS4 ( OsCyc1) and OsKSL4, which are involved in momilactone biosynthesis. OsCPS2 was particularly strongly induced, suggesting that it is one of the main mechanisms by which CA induces high levels of phytocassanes.