Saponins biosynthesis

A more detailed understanding of the biochemical pathways and enzymes involved in saponin biosynthesis will facilitate the development of plants with altered saponin content. In some cases, enhanced levels of saponins or the synthesis of novel saponins may be desirable (for example, for drug production 4 or improved disease resistance3,5,6), while for other plants, reduction in the content of undesirable saponins would be beneficial (for example, for legume saponins that are associated with antifeedant properties in animal feed7). This chapter is concerned with recent progress that has been made in the characterization of the enzymes and genes involved in the synthesis of these complex molecules and focuses on triterpenoid saponins. 

Triterpenoid saponins are synthesized via the isoprenoid pathway.4 The first committed step in triterpenoid saponin biosynthesis involves the cyclization of 2,3-oxidosqualene to one of a number of different potential products (Fig. 5.1).4,8 Most plant triterpenoid saponins are derived from oleanane or dammarane skeletons although lupanes are also common 4 This cyclization event forms a branchpoint with the sterol biosynthetic pathway in which 2,3-oxidosqualene is cyclized to cycloartenol in plants, or to lanosterol in animals and fungi. 

Kohara, A., Nakajima, C., Hashimoto, K., Ikenaga, T, Tanaka, H., Shoyama, Y, Yoshida, S. and Muranaka, T. (2005) A novel glucosyltransferase involved in steroid saponin biosynthesis in Solanum aculeatissimum. Plant Mol. Biol., 57, 225-39. 

KUROSAWA, Y., TAKAHARA, H., SHIRAIWA, M., UDP-glucuronic acidisoyasapogenol glucuronosyltransferase involved in saponin biosynthesis in germinating soybean seeds, Planta, 2002,5, 620-629. 

Takagi, K., Nishizawa, K., Hirose, A., Kita, A., Ishimoto, M., 2011. Manipulation of saponin biosynthesis by RNA interference mediated silencing of -amyrin synthase gene expression in soybean. Plant Cell Rep. 30, 1835-1846. 

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