Pectin RG-I rhamnosyltransferases represent a novel plant-specific glycosyltransferase family
Takenaka,Y., Kato,K., Ogawa-Ohnishi,M., Tsuruhama,K., Kajiura,H., Yagyu,K., Takeda,A., Takeda,Y., Kunieda,T., Hara-Nishimura,I., Kuroha,T., Nishitani,K., Matsubayashi,Y., Ishimizu,T.
Nature Plants doi: 10.1038/s41477-018-0217-7
Pectin is one of the three key cell wall polysaccharides in land plants and consists of three major structural domains: homogalacturonan, rhamnogalacturonan I (RG-I) and RG-II. Although the glycosyltransferase required for the synthesis of the
homogalacturonan and RG-II backbone was identified a decade ago, those for the synthesis of the RG-I backbone, which consists of the repeating disaccharide unit [2)--L-Rha-(1 4)--D-GalUA-(1], have remained unknown. Here, we report the identification and characterization of Arabidopsis RG-I:rhamnosyltransferases (RRTs), which transfer the rhamnose residue from UDP--L-rhamnose to RG-I oligosaccharides. RRT1, which is one of the four Arabidopsis RRTs, is a singlespanning transmembrane protein, localized to the Golgi apparatus. RRT1 was highly expressed during formation of the seed coat mucilage, which is a specialized cell wall with abundant RG-I. Loss-of-function mutation in RRT1 caused a reduction in the level of RG-I in the seed coat mucilage. The RRTs belong to a novel glycosyltransferase family, now designated GT106. This is a large plant-specific family, and glycosyltransferases in this family seem to have plant-specific roles, such as biosynthesis of plant cell wall polysaccharides.