The plant primary cell wall is a dynamic structure that exhibits considerable spatial and temporal variability in term of composition and organization, reflecting a balance between wall synthesis, deposition, reorganization and selective disassembly. This is achieved through the coordinated action of a battery of wall synthesizing and modifying enzymes that collectively provide a mechanism for regulating cell size, shape and cell-cell adhesion. Thus, selective modification of wall architecture is an integral part of processes as diverse as cellular growth, fruit softening, organ abscission, vascular differentiation and responses to pathogens
One of the key interactions in the primary wall of dicotyledons is formed between cellulose and the hemicellulose xyloglucan, which together typically comprise about two thirds of the dry wall mass. Xyloglucan binds non-covalently to cellulose, coating and cross-linking adjacent cellulose microfibrils
Cleavage of load-bearing xyloglucan cross-links by hydrolytic enzymes might be a means of achieving rapid wall loosening; however, in the absence of significant wall synthesis and reinforcement, the net result would be a reduction in wall tensile strength, with an increased potential for disastrous structural failure. Thinning of the wall as cell expansion proceeded would further exacerbate this weakening. An alternative mechanism for cleaving structurally important xyloglucan polymers emerged from an early hypothesis that cell growth involves... an endotransglycosylase that transfers a portion of a polysaccharide to itself
As of 2002, following a meeting of several research groups working with these enzymes/genes, a new unifying nomenclature has been adopted.