Isolation and Characterization of the Soybean Sg-3 Gene that is Involved in Genetic Variation in Sugar Chain Composition at the C-3 Position in Soyasaponins. (1st February 2018)

• Record Type: Journal Article
• Authors: Yano, Ryoichi; Takagi, Kyoko; Tochigi, Saeko; Fujisawa, Yukiko; Nomura, Yuhta; Tsuchinaga, Hiroki; Takahashi, Yuya; Takada, Yoshitake; Kaga, Akito; Anai, Toyoaki; Tsukamoto, Chigen; Seki, Hikaru; Muranaka, Toshiya; Ishimoto, Masao
• Is Part Of: Plant & cell physiology. Volume 59:Number 4(2018)
• Page Start: 792
• Page End: 805
• Publication Date: 2018-02-01
• Subjects: Glycosyltransferase -- Positional cloning -- Saponin polymorphism -- Soyasapogenol -- Soybean -- Sugar chain; Plant physiology -- Periodicals; Microbiology -- Periodicals; Cytology -- Periodicals; Cell Physiology -- Periodicals; Plant Physiological Phenomena -- Periodicals; Cytology; Microbiology; Plant physiology; Periodicals; 571.205
• DOI: 10.1093/pcp/pcy019
• Languages: English
• ISSNs: 0032-0781

Abstract

Abstract: Soyasaponins are specialized metabolites present in soybean seeds that affect the taste and quality of soy-based foods. The composition of the sugar chains attached to the aglycone moiety of soyasaponins is regulated by genetic loci such as sg-1, sg-3 and sg - 4 . Here, we report the cloning and characterization of the Sg-3 gene, which is responsible for conjugating the terminal (third) glucose (Glc) at the C-3 sugar chain of soyasaponins. The gene Glyma.10G104700 is disabled in the sg-3 cultivar, 'Mikuriya-ao', due to the deletion of genomic DNA that results in the absence of a terminal Glc residue on the C-3 sugar chain. Sg-3 encodes a putative glycosyltransferase (UGT91H9), and its predicted protein sequence has a high homology with that of the product of GmSGT3 ( Glyma.08G181000 ; UGT91H4), which conjugates rhamnose (Rha) to the third position of the C-3 sugar chain in vitro. A recombinant Glyma.10G104700 protein could utilize UDP-Glc as a substrate to conjugate the third Glc to the C-3 sugar chain, and introducing a functional Glyma.10G104700 transgene into the mutant complemented the sg-3 phenotype. Conversely, induction of a premature stop codon mutation in Glyma.10G104700 (W270*) resulted in the sg-3 phenotype, suggesting that Glyma.10G104700 was Sg-3 . The gmsgt3 (R339H) mutant failed to accumulate soyasaponins with the third Rha at the C-3 sugar chain, and the third Glc and Rha conjugations were both disabled in the sg-3 gmsgt3 double mutant. These results demonstrated that Sg-3 and GmSGT3 are non-redundantly involved in conjugation of the third Glc and Rha at the C-3 sugar chain of soyasaponins, respectively.