Plant Innate Immunity

The ability to discriminate between selfand nonself-molecules is characteristic of all living organisms. This feature forms the basis for the activation of innate immune responses uponmicrobial attack. Ifmicrobes bypass the external physical barrier, plants have evolved two classes of immune receptors to detect nonself-molecules to prevent further pathogen progress. One class consists of membrane-resident patternrecognition receptors that sense molecules from microbes, the so-called microbeassociatedmolecular patterns (MAMPs). The second class consists of plant resistance (R) proteins that have capacity to detect directly or indirectly isolate-specific pathogen effectors encoded by avirulence genes. These receptors are mainly intracellular. An alternative route is effector molecules that act as transcription factors. Signal transduction cascades link recognition and defence responses through second messengers, transcription factors and crosstalk between plant hormones to fine-tune the overall response.