Glucuronidation of type II arabinogalactan polysaccharides function in sexual reproduction of Arabidopsis

• Published in: The Plant journal : for cell and molecular biology 2022-01, Vol.109 (1), p.164-181
• Main Authors: Ajayi, Oyeyemi O., Held, Michael A., Showalter, Allan M.
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabinogalactan; arabinogalactan protein; Arabinose; Cell Wall - metabolism; Cell walls; embryo; Epitopes; Galactans - metabolism; Galactose; glucuronic acid; Glucuronic Acid - metabolism; glucuronosyltransferases; Glycan; Monosaccharides; Mucoproteins - genetics; Mucoproteins - metabolism; mutant; Mutants; Ovules; Plant Proteins - genetics; Plant Proteins - metabolism; Plant reproductive structures; Pollen; Pollen - enzymology; Pollen - genetics; Pollen - physiology; Pollen Tube - enzymology; Pollen Tube - genetics; Pollen Tube - physiology; Pollen tubes; Polysaccharides; Polysaccharides - metabolism; polytubey; Proteins; Reproduction; Reproduction (biology); Saccharides; seed set; Sexual reproduction; Stamens; Sugar
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.15562

SUMMARY Arabinogalactan proteins (AGPs) are complex, hyperglycosylated plant cell wall proteins with little known about the biological roles of their glycan moieties in sexual reproduction. Here, we report that GLCAT14A, GLCAT14B, and GLCAT14C, three enzymes responsible for the addition of glucuronic acid residues to AGPs, function in pollen development, polytubey block, and normal embryo development in Arabidopsis. Using biochemical and immunolabeling techniques, we demonstrated that the loss of function of the GLCAT14A, GLCAT14B, and GLCAT14C genes resulted in disorganization of the reticulate structure of the exine wall, abnormal development of the intine layer, and collapse of pollen grains in glcat14a/b and glcat14a/b/c mutants. Synchronous development between locules within the same anther was also lost in some glcat14a/b/c stamens. In addition, we observed excessive attraction of pollen tubes targeting glcat14a/b/c ovules, indicating that the polytubey block mechanism was compromised. Monosaccharide composition analysis revealed significant reductions in all sugars in glcat14a/b and glcat14a/b/c mutants except for arabinose and galactose, while immunolabeling showed decreased amounts of AGP sugar epitopes recognized by glcat14a/b and glcat14a/b/c mutants compared with the wild type. This work demonstrates the important roles that AG glucuronidation plays in Arabidopsis sexual reproduction and reproductive development. Significance Statement Despite arabinogalactan protein (AGP) abundance in reproductive tissues and function in plant sexual reproduction, little is known about the role of AGP glycan moieties in Arabidopsis sexual reproduction. We showed that three glucuronosyltransferase genes involved in the glucuronidation of AGP functions in pollen development, polytubey block, and normal embryo development in Arabidopsis. This work contributes to the better understanding of the genetic mechanisms involved in male gametophyte development and sexual fertilization in Arabidopsis.