Abstract
In soybean, triterpenoid saponin is one of the major secondary metabolites and is further classified into group A and DDMP saponins. Although they have known health benefits for humans and animals, acetylation of group A saponins causes bitterness and gives an astringent taste to soy products. Therefore, several studies are being conducted to eliminate acetylated group A saponins. Previous studies have isolated and characterized the Sg-5 (Glyma.15g243300) gene, which encodes the cytochrome P450 72A69 enzyme and is responsible for soyasapogenol A biosynthesis. In this study, we elucidated the molecular identity of a novel mutant of Glycine soja, ′CWS5095′. Phenotypic analysis using TLC and LC-PDA/MS/MS showed that the mutant ′CWS5095′ did not produce any group A saponins. Segregation analysis showed that the absence of group A saponins is controlled by a single recessive allele. The locus was mapped on chromosome 15 (4.3 Mb) between Affx-89193969 and Affx-89134397 where the previously identified Glyma.15g243300 gene is positioned. Sequence analysis of the coding region for the Glyma.15g243300 gene revealed the presence of four SNPs in ′CWS5095′ compared to the control lines. One of these four SNPs (G1127A) leads to the amino acid change Arg376Lys in the EXXR motif, which is invariably conserved among the CYP450 superfamily proteins. Co-segregation analysis showed that the missense mutation (Arg376Lys) was tightly linked with the absence of group A saponins in ′CWS5095′. Even though Arg and Lys have similar chemical features, the 3D modelled protein structure indicates that the replacement of Arg with Lys may cause a loss-of-function of the Sg-5 protein by inhibiting the stable binding of a heme cofactor to the CYP72A69 apoenzyme.
Highlights
Saponins are glycosylated compounds that are widely distributed in plants, and have different biological and pharmaceutical properties [1,2]
oxidosqualene cyclases (OSCs), CYP450s, and UGTs are the three main enzymes involved in the biosynthesis of saponins [3]
Majority of A-type and a few non-A-type CYP450s are involved in the biosynthesis of secondary metabolites such as terpenoids, flavonoids, alkaloids and phytoalexins [42, 43]
Summary
Saponins are glycosylated compounds that are widely distributed in plants, and have different biological and pharmaceutical properties [1,2]. Triterpenoid saponins are widely distributed in higher plants [1,2]. They are composed of triterpene aglycone, with one or more sugar chains. In the first step of saponin synthesis, 2,3-oxidosqualene is cyclized by oxidosqualene cyclases (OSCs) to produce polycyclic triterpene [4,5]. After cyclization of the basic triterpene backbone, the backbone is oxidized to produce a hydrophobic aglycone called sapogenin. The step is to synthesize saponins via O-glycosylation of the aglycones. The biological roles of triterpenoid saponins in plants remain underexplored
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
