The Role of the Plant-Specific ALTERED XYLOGLUCAN9 Protein in Arabidopsis Cell Wall PolysaccharideO-Acetylation  

Abstract

A mutation in the ALTERED XYLOGLUCAN9 (AXY9) gene was found to be causative for the decreased xyloglucan acetylation phenotype of the axy9.1 mutant, which was identified in a forward genetic screen for Arabidopsis (Arabidopsis thaliana) mutants. The axy9.1 mutant also exhibits decreased O-acetylation of xylan, implying that the AXY9 protein has a broad role in polysaccharide acetylation. An axy9 insertional mutant exhibits severe growth defects and collapsed xylem, demonstrating the importance of wall polysaccharide O-acetylation for normal plant growth and development. Localization and topological experiments indicate that the active site of the AXY9 protein resides within the Golgi lumen. The AXY9 protein appears to be a component of the plant cell wall polysaccharide acetylation pathway, which also includes the REDUCED WALL ACETYLATION and TRICHOME BIREFRINGENCE-LIKE proteins. The AXY9 protein is distinct from the TRICHOME BIREFRINGENCE-LIKE proteins, reported to be polysaccharide acetyltransferases, but does share homology with them and other acetyltransferases, suggesting that the AXY9 protein may act to produce an acetylated intermediate that is part of the O-acetylation pathway.

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Producing corrosive acetic acid in bio-oil (Mante et al, 2014), acetyl groups on cell wall polymers are another potential target for genetic engineering of "pyrolysis crops. " Three enzyme classes, including the reduced wall acetylation (RWA) proteins, Trichome birefringence-like (TBL) and Altered Xyloglucan (AXY) proteins acetylate cell wall polysaccharides (Lee et al, 2011;Xiong et al, 2013;Schultink et al, 2015). A mutant of the dicot reference plant, Arabidopsis thaliana, which lacks expression of all four RWA genes, shows a 40% reduction in secondary wall-associated acetyl groups (Lee et al, 2011).…”

“…Advances in understanding cell wall biosynthesis, including genes responsible for synthesizing the major polymer classes (Bonawitz and Chapple, 2010;Scheller and Ulvskov, 2010;Pauly et al, 2013) and covalent interactions among them (Chiniquy et al, 2012;Bartley et al, 2013;Schultink et al, 2015); regulation of expression of the cell wall biosynthesis genes (Zhao and Dixon, 2011); and metal ion transport proteins that determine the abundance and distribution of plant mineral content (Ma et al, 2006;Yamaji and Ma, 2009;Zhong and Ye, 2015), lay the foundation for genetically engineering bioenergy crop cell wall content and structure. For example, lignin is an important target for genetic engineering for pyrolysis since the major lignin-derived products have a lower O:C ratio, a higher energy value, and are more stable than sugar-derived products (Tanger et al, 2013;Mante et al, 2014).…”

Two Trichome Birefringence-Like Proteins Mediate Xylan Acetylation, Which Is Essential for Leaf Blight Resistance in Rice

“…Three groups of proteins have been identified to be involved in O-acetylation of cell wall polymers (Gille et al, 2011b;Manabe et al, 2011;Schultink et al, 2015), in which TBLs constitute the largest gene family. Forty-six TBL members are present in the Arabidopsis genome (Gille and Pauly, 2012), but only a few of those TBLs have been characterized (Gille et al, 2011b;Xiong et al, 2013;Yuan et al, 2013Yuan et al, , 2016aYuan et al, , 2016c.…”

“…AXY9 is a recently reported Golgi-localized protein bearing only one transmembrane domain. The decrease in acetylation level on multiple polymers such as XyG and xylan in the axy9 mutant indicates its involvement in O-acetylation, but its precise function remains elusive (Schultink et al, 2015). TBL proteins share two conserved domains, the TBL and DUF231 domain, with the Arabidopsis Trichome Birefringence protein (Potikha and Delmer, 1995;Bischoff et al, 2010).…”

“…One possibility is that this modification can enhance the interaction of the hemicelluloses with other wall polymers (Busse-Wicher et al, 2014), leading to the rigid wall conformation to facilitate relevant physiological functions. Several Arabidopsis mutants that have the compromised acetyl-xylan exhibit collapsed xylem vessels and abnormal growth status (Lee et al, 2011;Xiong et al, 2013;Schultink et al, 2015;Yuan et al, 2016c). Another potential function of polymer O-acetylation is to protect plants against invading microorganism and environmental stresses.…”