Connecting Homogalacturonan-Type Pectin Remodeling to Acid Growth

The primary cell wall is composed of a polysaccharide matrix whose chemical composition and remodeling affects plant development. Regulation of HG structure plays a central role in the control of cell elongation. Cell growth has been described as being promoted by low apoplast pH. Numerous studies have reported the occurrence of localized cell wall acidification during cell elongation. Perturbations in the expression of pectin-remodeling enzymes result in alteration of development. Modifications in HG structure can underlie changes in cell wall rheology, with consequences for development. Controlled cell elongation requires fine-tuning of pectin-remodeling enzyme activities which are related to spatial and temporal changes in apoplast pH. According to the ‘acid growth theory’, cell wall acidification controls cell elongation, therefore plant growth. This notably involves changes in cell wall mechanics through modifications of cell wall polysaccharide structure. Recently, advances in cell biology showed that changes in cell elongation rate can be mediated by the remodeling of pectins, and in particular of homogalacturonans (HGs). Their demethylesterification appears to be a key element controlling the chemistry and the rheology of the cell wall. We postulate that precise and dynamic modulation of extracellular pH plays a central role in the control of HG-modifying enzyme activities, and in particular those of pectin methylesterases and polygalacturonases. We propose that acid growth requires dynamic HG remodeling through the tight control of cell wall pH. According to the ‘acid growth theory’, cell wall acidification controls cell elongation, therefore plant growth. This notably involves changes in cell wall mechanics through modifications of cell wall polysaccharide structure. Recently, advances in cell biology showed that changes in cell elongation rate can be mediated by the remodeling of pectins, and in particular of homogalacturonans (HGs). Their demethylesterification appears to be a key element controlling the chemistry and the rheology of the cell wall. We postulate that precise and dynamic modulation of extracellular pH plays a central role in the control of HG-modifying enzyme activities, and in particular those of pectin methylesterases and polygalacturonases. We propose that acid growth requires dynamic HG remodeling through the tight control of cell wall pH. the space that surrounds a plant cell. It notably comprises the interfibrillar and intermicellar spaces of the cell walls. crosslink between divalent cations (mainly calcium ions) and demethylerified pectins. In vitro, these structures can increase the stiffness of a gel. In vivo, the occurrence of such structures is discussed (Box 1). a type of pectin homopolymer which can be methylesterified and/or acetylated. The regulation of its degree of methylesterification appears central to the control of plant development. small peptides that mediate inhibition of plasma membrane H+-ATPase, and that are thus involved in the regulation of apoplast pH. resistance to deformation. Applied to cell walls, it corresponds to changes in cell wall chemistry and structure.