Xyloglucan

Xyloglucan is a hemicellulose polysaccharide and a major component of the primary cell walls of many plants, particularly dicots and several monocots. It has a beta-1,4-glucan (cellulose-like) backbone with branched side chains of xylose attached at the O-6 position. These xylose residues are often further substituted with galactose and, in some species, fucose, yielding motifs such as XXXG, XXLG, XLLG, and XLFG.

The structure and composition of xyloglucan vary among species, giving different patterns of branching and side-chain substitutions. The repeating motif XXXG is common, but the exact side-chain decorations influence its physical properties and interactions with other wall components. Xyloglucan is synthesized in the Golgi apparatus, secreted in vesicles, and integrated into the cell wall where it associates with cellulose microfibrils to form an integrated network.

In the cell wall, xyloglucan functions as a cross-linker between cellulose microfibrils, contributing to wall strength and cohesion while allowing controlled extensibility. Its mechanical role is modulated by wall remodeling enzymes, particularly xyloglucan endotransglucosylases/hydrolases (XTH), which cut and re-join xyloglucan chains to rearrange the network during cell expansion and growth.

Ecological and developmental relevance varies; xyloglucan is a major determinant of wall mechanics in many plant tissues. In contrast, grasses rely more on other hemicelluloses such as glucuronoarabinoxylans, reflecting differences in cell wall architecture among plant lineages.