Regulation of plant growth by polysaccharide synthesis and incorporation into the cell wall

Plant cells can grow and increase their volume by several orders of magnitude. Growth is associated with expansion of the cell wall, a process that is thought to be primarily regulated by the coupling between cell wall remodelling and cell wall mechanics. Nevertheless, expansion requires the addition of new material to the cell wall to prevent wall thinning and bursting. Here, we consider the potential regulation of expansion by synthesis and integration into the wall of cellulose and matrix polysaccharides-pectins and hemicelluloses. We review experimental data about synthesis and transport of polysaccharide precursors, synthesis of polysaccharides, delivery to the wall of matrix polysaccharides or of cellulose synthases, and incorporation of polysaccharides into the wall, as well as the role of turgor pressure in these processes. In most cases, it appears that regulation of expansion by integration is both direct-mostly negative for cellulose and positive for matrix polysaccharides-and indirect-through cell wall integrity sensing. As a case study, we consider the phenomenon of stored growth: after a transient drop in turgor, a growth burst may occur so that the tissue reaches the size it would have without the drop in turgor, suggesting that growth was 'stored' during the phase of low turgor. Finally, we propose that these entangled processes can be analysed using the same framework as gene regulatory networks, which may guide future research.