Identification of Two Key Enzymes in Xylan Synthesis and Acetylation in Plant Cell Walls

The Science

Only a few dozen of the thousands of genes involved plant cell wall biosynthesis have been identified and confirmed. Xylan, a part of hemicellulose, is a major component of plant cell walls and the third most abundant polysaccharide on Earth. The key enzymes responsible for elongation of the xylan backbone and addition of acetyl groups had not been identified, but researchers from the BioEnergy Science Center of Oak Ridge National Laboratory recently identified two key enzymes for the synthesis of this polysaccharide and confirmed their function biochemically. Mutations that impair synthesis of the xylan backbone give rise to plants with collapsed xylem cells and poor growth. Phenotypic analysis of these mutants has implicated many possible proteins in xylan biosynthesis. To further investigate the role of the mutant genes in xylan biosynthesis, recombinant tagged proteins encoded by the Arabidopsis thaliana genes, IRX10-L and ESK1/TBL29, were expressed in vitro and purified. Enzymatic activity of these proteins was inferred from the similarity of their primary amino acid sequence to enzymes of known function. Their enzyme activity was analyzed in vitro by mass spectroscopy and nuclear magnetic resonance. This direct biochemical evidence confirmed the A. thaliana protein IRX10-L enzyme as the xylan synthase and ESK1/TBL29 as the archetypal plant polysaccharide O-acetyltransferase. Thus, two key enzymes for two critical process in xylan (and secondary plant cell wall) synthesis now have been identified, purified, and confirmed. These findings will accelerate understanding of and the ability to manipulate plant cell wall structures for advanced renewable feedstocks for conversion into sugars and fuels or into valuable products such as biomaterials.


Xylan is the third most abundant glycopolymer on earth after cellulose and chitin. As a major component of wood, grain and forage, this natural biopolymer has far-reaching impacts on human life. This highly acetylated cell wall polysaccharide is a vital component of the plant cell wall, which functions as a molecular scaffold, providing plants with mechanical strength and flexibility. By identifying the elusive xylan synthase and establishing ESK1/TBL29 as the archetypal plant polysaccharide O-acetyltransferase, researchers have resolved two long-standing questions in plant cell wall biochemistry. These findings shed light on integral steps in the molecular pathways used by plants to synthesize a major component of the world’s biomass and expand the toolkit for producing glycopolymers with valuable properties.

BER Program Manager

Shing Kwok

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Urbanowicz, B. R., M. J. Peña, H. A. Moniz, K. W. Moremen, and W. S. York. 2014. “Two Arabidopsis Proteins Synthesize Acetylated Xylan In Vitro,” The Plant Journal 80(2), 197-206. DOI:10.1111/tpj.12643.