Plant cells are surrounded by a rigid wall made up of cellulose microfibrils, pectins, hemicelluloses, and lignin. This cell wall provides structure and protection for plant cells. In grasses and in dicot secondary cell walls, the major hemicellulose is a polymer of β-(1,4)-linked xylose units called xylan. Unlike cellulose--which is synthesized by large complexes at the plasma membrane--xylan is synthesized by enzymes in the Golgi apparatus. Xylan synthesis thus requires the coordinated action and regulation of these synthetic enzymes as well as others that synthesize and transport substrates into the Golgi. Recent research has identified several genes involved in xylan synthesis, some of which have already been used in engineering efforts to create plants that are better suited for biofuel production. Copyright © 2013 Elsevier Ltd. All rights reserved.