The plant cell wall: Barrier and facilitator of environmental perception

Abstract

The plant cell wall is an assembly of ions, small molecules, macromolecules, and higher-order structures that surround plant cells. All plant cells start with a primary cell wall, the major components of which are polysaccharides - cellulose, hemicelluloses, and pectin. The primary cell wall is a dynamic structure that undergoes constant remodeling through synthesis, modification, and altered interactions of its macromolecular and other contents. Cells with only a primary cell wall have the ability to grow/expand or not to do so in response to a variety of intrinsic and extrinsic environmental cues through mechanisms that involve the cell wall. Depending on the environment, the cell wall may extend irreversibly with the increasing volume of an expanding cell or the cell wall may become rigid preventing the cell from expanding. How do a variety of abiotic and biotic signals interact with and influence the cell wall? Significant advances have been made in the last few years in our understanding of the physical basis of the signals, their receptors, and the downstream events that lead to remodeling of the cell wall. While some signal molecules are not cell wall-derived, for example, those from pathogens (PAMPs), in other cases, the cell wall is a source of signals, either in the form of signaling molecules (DAMPs) or changes in the composition/ structure of the wall. It is believed that these signals are recognized by cell surface receptors that upon activation trigger, among other effects, change in the expression of a number of wall-related genes that code for wall-modifying proteins. In a feedback response, signals from the wall are sensed for modification of the wall. Many of the signaling pathways that utilize the cell wall as both a source of signals and a response target are the ones that operate during pattern-triggered immunity (PTI) and in the maintenance of cell wall integrity (CWI).