AUTHOR=Wachananawat Bussarin , Kuroha Takeshi , Takenaka Yuto , Kajiura Hiroyuki , Naramoto Satoshi , Yokoyama Ryusuke , Ishizaki Kimitsune , Nishitani Kazuhiko , Ishimizu Takeshi 

TITLE=Diversity of Pectin Rhamnogalacturonan I Rhamnosyltransferases in Glycosyltransferase Family 106

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00997

DOI=10.3389/fpls.2020.00997

ISSN=1664-462X

ABSTRACT=<p>Rhamnogalacturonan I (RG-I) comprises approximately one quarter of the pectin molecules in land plants, and the backbone of RG-I consists of a repeating sequence of [2)-α-L-Rha(1-4)-α-D-GalUA(1-] disaccharide. Four <italic>Arabidopsis thaliana</italic> genes encoding RG-I rhamnosyltransferases (AtRRT1 to AtRRT4), which synthesize the disaccharide repeats, have been identified in the glycosyltransferase family (GT106). However, the functional role of RG-I in plant cell walls and the evolutional history of RRTs remains to be clarified. Here, we characterized the sole ortholog of AtRRT1–AtRRT4 in liverwort, <italic>Marchantia polymorpha</italic>, namely, MpRRT1. MpRRT1 had RRT activity and genetically complemented the At<italic>RRT1</italic>-deficient mutant phenotype in <italic>A. thaliana</italic>. However, the Mp<italic>RRT1</italic>-deficient <italic>M. polymorpha</italic> mutants showed no prominent morphological changes and only an approximate 20% reduction in rhamnose content in the cell wall fraction compared to that in wild-type plants, suggesting the existence of other <italic>RRT</italic> gene(s) in the <italic>M. polymorpha</italic> genome. As expected, we detected RRT activities in other GT106 family proteins such as those encoded by Mp<italic>RRT3</italic> in <italic>M. polymorpha</italic> and <italic>FRB1/</italic>At<italic>RRT8</italic> in <italic>A. thaliana</italic>, the deficient mutant of which affects cell adhesion. Our results show that <italic>RRT</italic> genes are more redundant and diverse in GT106 than previously thought.</p>