Arabidopsis GALACTURONOSYLTRANSFERASE (GAUT) 1 synthesizes a homogalacturonan tightly bound to the cell wall and required for cell expansion
Melani A. Atmodjo (United States)1 2 3 4; Robert A. Amos (United States)1 2; Alexis Peaucelle (France)5; Kalina T. Haas (France)5; John Glushka (United States)1; Li Tan (United States)1; Ian M. Black (United States)1; Alban Mariette (France)5; Thierry Desprez (France)5; P. Jarod Glatz (United States)1; Darryn C. Amanda (United States)1; Ioana Emerich (United States)1; Joshua Indech (United States)1; Sivakumar Pattathil (United States)1 3; Sindhu Kandemkavil (United States)1; Stefan Eberhard (United States)1; Parastoo Azadi (United States)1; Michael G. Hahn (United States)1 6 3; Debra Mohnen (United States)1 2 3 4;
1 - Complex Carbohydrate Research Center, University of Georgia; 2 - Department of Biochemistry and Molecular Biology, University of Georgia; 3 - DOE BioEnergy Science Center; 4 - DOE Center for Bioenergy Innovation; 5 - Université Paris-Saclay, INRAE, AgroParisTech, Institut Jean-Pierre Bourgin (IJPB); 6 - Department of Plant Biology, University of Georgia;
Keywords: arabidopsis; homogalacturonan; cell expansion;
Abstract Topics: Theme 1: Pectins: Structure, Remodeling, and Function
Type of Presentation: Oral Communication

Abstract text: Arabidopsis GALACTURONOSYLTRANSFERASE1 (GAUT1) initiates pectic homogalacturonan (HG) biosynthesis and elongates HG acceptors in vitro. Its biological function and structure of the HG-containing polymer(s) it synthesizes remain unclear. Here we show that Arabidopsis gaut1 homozygous mutants grow as severely dwarfed seedlings that fail to yield mature plants due to defective cell expansion/elongation. Homozygous gaut1-1 mutant suspension cells are smaller than wild type (WT) with reduced HG:galacturonosyltransferase activity and wall galacturonic acid (GalA) content. Sequential extraction of gaut1-1 suspension cell walls with increasingly harsh solvents revealed a significant loss of GalA in the final 4M KOH post-chlorite extract. Digestion of this extract with endopolygalacturonase and high percentage polyacrylamide gel electrophoresis revealed doublet bands in WT extract downregulated in gaut1-1 and identified by NMR analysis as rhamnogalacturonan II (RG-II). The bulk of RG-II, generally extracted in early ammonium oxalate and sodium carbonate fractions, was not reduced in the gaut1-1 mutant. Super resolution microscopy revealed a decrease and disorganization of HG nanofilaments in hypocotyl and callus gaut1-1 walls compared to WT. The results support a model of GAUT1 synthesizing a unique HG held tightly in the cell wall, associated with a unique population of RG-II, and required for HG nanofilament organization and cell expansion/elongation.