Xylan (木聚糖) and cellulose (纤维素) are abundant polysaccharides (多糖) in vascular plants (维管植物) and essential for secondary cell wall strength. Acetate or glucuronic acid (醋酸，葡糖醛酸) decorations are exclusively found on even-numbered residues in most of the glucuronoxylan polymer (葡糖醛酸聚合物). It has been proposed that this even-specific positioning of the decorations might permit docking (对接) of xylan onto the hydrophilic face (亲水面) of a cellulose microfibril1,2,3 (纤维素微纤丝). Consequently, xylan adopts a flattened ribbon-like (扁平带状) twofold screw (双螺旋) conformation (构象) when bound to cellulose in the cell wall4. Here we show that ESKIMO1/XOAT1/TBL29, a xylan-specific O-acetyltransferase, is necessary for generation of the even pattern of acetyl esters (醋酸基) on xylan in Arabidopsis. The reduced acetylation in the esk1 mutant deregulates (解除) the position-specific activity of the xylan glucuronosyltransferase GUX1 (木聚糖葡萄糖苷酸转移酶), and so the even pattern of glucuronic acid (葡糖醛酸) on the xylan is lost. Solid-state NMR (固体核磁共振) of intact cell walls shows that, without the even-patterned xylan decorations, xylan does not interact normally with cellulose fibrils (纤维素纤维). We conclude that the even pattern of xylan substitutions seen across vascular plants enables the interaction of xylan with hydrophilic faces of cellulose fibrils, and is essential for development of normal plant secondary cell walls.

Published online: October 9, 2017.