Some plants recognize specific pathogen-derived substances

Within a species, individual plants often differ greatly in their resistance to microbial pathogens. These differences often lie in the speed and intensity of a plant's reactions. Resistant plants respond more rapidly and more vigorously to pathogens than do susceptible plants. Hence it is important to learn how plants sense the presence of pathogens and initiate defensive responses. A first line of resistance is provided by a system that recognizes broad categories of pathogens. Plants have a variety of receptors that recognize so-called microbeassociated general molecular patterns (MAMPs). These elicitors are evolutionary conserved pathogenderived molecules such as structural elements from the fungal cell wall or the bacterial flagellum. MAMPs are recognized by specific receptors, which then activate specific plant defensive responses, including massive phytoalexin production. The effectiveness of these MAMP receptors (or pattern recognition receptors) is amazing, considering the

For example, the flagellin (flg22) receptor FLS2 enables the plant to recognize all mobile (flagellated) bacteria. Similarly, the as yet uncharacterized receptor for pep13 enables plants to recognize all oomycete pathogens. Consequently, those pathogens cannot cause disease. This form of defensive strategy is also referred to as innate immunity.

A single encounter with a pathogen may increase resistance to future attacks