The molecular mechanism of polymer O-acetylation in plants is unknown limiting our ability to tailor plants with defined O-acetylation levels. In an attempt to gain insights into genes/proteins involved in polysaccharide O-acetylation we screened a chemically mutagenized plant population for mutants with altered hemicellulose structures (axy-mutants). One of the mutants, axy4, exhibited a 20% reduction in hemicellulose O-acetylation. Mapping of the mutation resulted in the identification of a gene (AXY4) encoding a protein of unknown function, which we propose represents a polysaccharide specific O-acetyltransferase. AXY4 is part of a multigene family and hence it is likely that the related homologs are responsible for acetylating other wall polymers.
A mechanistic model encompassing our current knowledge of polysaccharide O-acetylation will be presented. Since the identification of AXY4 enables us to altered polymer O-acetylation in planta, the impact of O-acetylation on wall recalcitrance to enzymatic degradation will be discussed.