Plants have an efficient system of innate immunity which is based on the effective detection of potentially harmful microorganisms and rapid induction of defense responses. The first level of plant immunity is the basal immunity which is induced by the conserved molecular structures of microbes such as bacterial flagellins or fungal chitin, or molecules that result from the interaction of plants with pathogens, for example oligosaccharides and peptides ("danger signals"). Plants recognize these inducers through receptors localized to the plasma membrane, represented mainly receptor-like protein kinases or receptor-like proteins. Activation of the receptor by a ligand triggers a complex network of signaling events which eventually cause an array of plant defense responses to prevent further spread of the pathogen.