Chemoperception of microbial signals in plant cells

Abstract

Plants have exquisitely sensitive chemoperception systems for signal substances derived from microorganisms. Among the microbial substances that plants can perceive at threshold concentrations of approximately 10-12-10-10 M are oligosaccharides and lipo-oligosaccharides, peptides and glycopeptides, and lipophilic substances such as ergosterol. In many cases, the perception systems of plants recognize "non-self" molecules characteristic of fungi and bacteria with a high degree of specificity, and some of them show rapid desensitization, leading to a refractory state reminiscent of smell perception. Specific binding sites for microbial signal molecules have been found on intact plant cells and on isolated plasma membranes; they probably function as receptors. An intriguing question is whether the products of some of the recently identified resistance genes are homologous to such receptors. Chemoperception of microbial substances may not only play a role for the plant in active defense and pathogen resistance, but also in mutualistic symbiosis and in the acquisition of basic information about microbes in the environment.