Revealing the structural and functional diversity of plant cell walls

The extensive knowledge of the chemistry of isolated cell wall polymers, and that relating to the identification and partial annotation of gene families involved in their synthesis and modification, is not yet matched by a sophisticated understanding of the occurrence of the polymers within cell walls of the diverse cell types within a growing organ. Currently, the main sets of tools that are used to determine cell-type-specific configurations of cell wall polymers and aspects of cell wall microstructures are antibodies, carbohydrate-binding modules (CBMs) and microspectroscopies. As these tools are applied we see that cell wall polymers are extensively developmentally regulated and that there is a range of structurally distinct primary and secondary cell walls within organs and across species. The challenge now is to document cell wall structures in relation to diverse cell biological events and to integrate this knowledge with the emerging understanding of polymer functions.

Introduction

Plant cell walls are highly complex and dynamic cell compartments that underpin many aspects of cell development, organ growth and organ properties. In the study of cell walls in relation to growth mechanisms considerable knowledge of the component cell wall polysaccharides has been established and at the same time, schematic models of cell wall structure and of how the polysaccharide components of cell walls fit together to generate the appropriate properties have been proposed and refined [1]. However, such models are currently generic, aimed at understanding ‘the plant cell wall’ and generally propose a model that is applied to all primary or all secondary cell walls. Biochemical analyses and genome sequencing has led to a documentation of the, often large, gene families that are involved in the synthesis and modification of cell wall components, but the detailed understanding of how these sets of genes impact upon the construction and maintenance of cell walls during growth is limited. Central to all these studies are the actual cell walls that function in diverse cell types during growth. Cell walls generate the mechanical properties that deal with tensile and compressive forces and also regulate cell expansion and cell adhesion. We have only a limited knowledge of the diversity of the in situ cell wall macromolecular configurations that can occur in a developing organ [2]. In short, the known structural complexity of cell wall polysaccharide classes and the known extensive repertoires of carbohydrate active genes are not matched by a sophisticated view of polymer occurrences and functions within cell walls in the context of cells, tissues or organs.