A Novel (1,4)-β-Linked Glucoxylan Is Synthesized by Members of the <i>Cellulose Synthase-Like F</i> Gene Family in Land Plants

Abstract

As a significant component of monocot cell walls, (1,3;1,4)-β-glucan has conclusively been shown to be synthesized by the cellulose synthase-like F6 protein. In this study, we investigated the synthetic activity of other members of the barley (<i>Hordeum vulgare</i>) <i>CslF</i> gene family using heterologous expression. As expected, the majority of the genes encode proteins that are capable of synthesizing detectable levels of (1,3;1,4)-β-glucan. However, overexpression of <i>HvCslF3</i> and <i>HvCslF10</i> genes resulted in the synthesis of a novel linear glucoxylan that consists of (1,4)-β-linked glucose and xylose residues. To demonstrate that this product was not an aberration of the heterologous system, the characteristic (1,4)-β-linkage between glucose and xylose was confirmed to be present in wild type barley tissues known to contain <i>HvCslF3</i> and <i>HvCslF10</i> transcripts. This polysaccharide linkage has also been reported in species of <i>Ulva</i>, a marine green alga, and has significant implications for defining the specificity of the cell wall content of many crop species. This finding supports previous observations that members of a single CSL family may not possess the same carbohydrate synthetic activity, with the CSLF family now associated with the formation of not only (1,3)- and (1,4)-β-glucosidic linkages, but also (1,4)-β-glucosidic and (1,4)-β-xylosidic linkages.