Enhanced triterpene saponin biosynthesis and root nodulation in transgenic barrel medic (Medicago truncatula Gaertn.) expressing a novel β‐amyrin synthase (AsOXA1) gene

Abstract

Summary Triterpene saponins are a group of bioactive compounds abundant in the genus Medicago, and have been studied extensively for their biological and pharmacological properties. In this article, we evaluated the effects of the ectopic expression of AsOXA1 cDNA from Aster sedifolius on the production of triterpene saponins in barrel medic (Medicago truncatula Gaertn.). AsOXA1 cDNA encodes β‐amyrin synthase, a key enzyme involved in triterpene saponin biosynthesis. One of the four transgenic lines expressing AsOXA1 accumulated significantly larger amounts of some triterpenic compounds in leaf and root than did control plants. In particular, the leaf exhibited significantly higher levels of bayogenin, medicagenic acid and zanhic acid. The amounts of medicagenic acid and zanhic acid, which represent the core of the M. truncatula leaf saponins, were 1.7 and 2.1 times higher, respectively, than the amounts extracted from the control line. In root, the production of bayogenin, hederagenin, soyasapogenol E and 2β‐hydroxyoleanolic acid was increased significantly. The increase in the total amounts of triterpenic compounds observed in the leaves of transgenic lines correlated with the AsOXA1 expression level. Interestingly, the plants expressing AsOXA1 showed, under different growth conditions, improved nodulation when compared with the control line. Nodulation enhancement was also accompanied by a significant change in the soyasapogenol B content. Our results indicate that the ectopic expression of AsOXA1 in barrel medic leads to a greater accumulation of triterpene saponins and enhanced root nodulation.

RNA-Seq analysis discloses early senescence and nucleolar dysfunction triggered by Tdp1α depletion in Medicago truncatula

“…cv. Jemalong (M9-10a genotype) were grown and micropropagated in vitro as described by Confalonieri et al (2009). A detailed description of constructs is provided in the Supplementary data avbailable at JXB online.…”

Metabolite Profiling of Triterpene Saponins in Medicago truncatula Hairy Roots by Liquid Chromatography Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…7 In a more recent study, however, zanhic acid could not be detected in M. truncatula roots. 27 Similarly, no zanhic acid-containing compounds were detected in the hairy roots. Hairy root cultures are known to accumulate secondary metabolites that are normally produced in "natural" roots of differentiated plants.…”

“…No saponins of M. truncatula that contain soyasapogenol A as the aglycone had been described, but the compound had been shown to occur in M. truncatula as a sapogenin. 27 Hence, the two saponins containing this aglycone were tentatively identified as soyasapogenol A glycosides.…”

The Sg-1 Glycosyltransferase Locus Regulates Structural Diversity of Triterpenoid Saponins of Soybean

“…Peak 1 (saponin Aa, m/z = 1365.6) or peak 2 (saponin Ab, m/z = 1437.6) was as well as direct reduction of O 2 by nitrogenase, hydrogenase, and ferredoxin in bacteroids (Dalton, 1995). Ectopic expression of the b-amyrin synthase gene (OXA1) of Aster sedifolius resulted in increased accumulation of triterpene saponins and enhanced root nodulation in barrel medic (Medicago truncatula) (Confalonieri et al, 2009). In addition, exogenous treatments with group B saponins stimulate root growth in lettuce (Lactuca sativa) and Arabidopsis thaliana (Tsurumi and Ishizawa, 1997;Tsurumi et al, 2000).…”