Molecular biology of the plant cell wall: searching for the genes that define structure, architecture and dynamics

The plant cell wall is a highly organized composite that may contain many different polysaccharides, proteins, and aromatic substances. These complex matrices define the features of individual cells within the plant body. Ultimately, the plant wall functions as the determinant of plant morphology. The importance of the plant cell wall is revealed in the shear number of genes that are likely to be involved in cell wall biogenesis, assembly, and modification. For example, over 17% of the 25498 Arabidopsis genes have signal peptides, and over 400 proteins have been identified that reside in the wall (Arabidopsis Genome Initiative, 2000). If just one-half of the proteins with signal peptides function in the biosynthesis, assembly, and modification of the walls, then well over 2000 genes are likely to participate in wall biogenesis during plant development. This number is considerably larger if all the cytosolic proteins that function in substrate generation are included. Beyond this, some integral membrane-associated proteins, such as cellulose synthase, obviously function in cell wall bio genesis but do not contain signal peptides. Thus, it is likely that some 15% of the Arabidopsis genome is dedicated to cell wall biogenesis and modification. Of these, only small subsets have been characterized.