The plant cell wall is a dynamic structural and functional entity made up of polysaccharides and proteins. Besides providing structural integrity to the cell, the wall provides a mechanism for cell growth, cell-to-cell communication and participates in environmental signal transduction. Many microbial pathogens and symbionts of plants produce plant cell wall-degrading enzymes as important components of their virulence or interactive arsenal. Depolymerization of wall carbohydrate polymers generate oligomers of varying degrees of polymerization that serve to notify the plant as well as the invading microorganism of the presence of each other. Our understanding of theprecise mechanisms underlying plant cell wall-derived signal uptake or reception in microbial pathogens and symbionts, is in its infancy. Uptake systems for polysaccharide-derived monomers and dimers have been described. Several proteins have been recognized to play a structural role in the cell wall. Although many plant pathogens produce proteases, reports of uptake systems for peptides and oligopeptides in phytopathogenic bacteria are scarce. Given that transporters in general are the most abundant class of proteins identified in bacteria based on whole genome analysis, it is especially noteworthy that so few uptake systems have been identified for plant cell wall-derived molecules in microorganisms. This represents a fertile area for investigation.