Pathogen derived elicitors: searching for receptors in plants

Recognition of potential pathogens is central to plants' ability to defend themselves against harmful microbes. Plants are able to recognize pathogen-derived molecules; elicitors that trigger a number of induced defences in plants. Microbial elicitors constitute a bewildering array of compounds including different oligosaccharides, lipids, peptides and proteins. Identifying the receptors for this vast array of elicitors is a major research challenge. Only in a very few cases has the cognate receptor for a particular elicitor been identified. Biochemical studies have resulted in the characterization of some elicitor binding proteins that may be part of the recognition complex. Transmembrane receptor-like protein kinases (RLKs) constitute one of the most likely categories of receptors involved in pathogen perception. Some of these serine/threonine kinases have been identified as resistance or R genes, others as induced by pathogens or elicitors. One of the RLKs belonging to a leucine rich repeat (LRR) class of putative receptor kinases was recently identified as a receptor for bacterial flagellin, and the underlying signal pathway leading to activation of defence genes was elucidated. These and other recent studies have revealed intriguing similarities in elicitor recognition and defence signalling processes in plant and animal hosts suggesting a common evolutionary origin of eukaryotic defence mechanisms.