Non-specific defense against plant pathogens can be passive (constitutive) or active (induced by microbes). The activation of general resistance follows the perception of the pathogenic threat. The first class of plant receptors recognizes molecular patterns associated with pathogens / microbes (PAMPs / MAMPs) in a nonspecific way. These are resident membrane receptors, also called pattern recognition receptors, PRRs. Plant PRRs are the source of extremely complex molecular signaling immune machinery. A transmembrane receptor that binds to a ligand then triggers the signalling would be the most simplistic scenario. Yet, in many cases, the recognition scheme would also include co-receptors, as well as regulatory proteins, which activate PRRs leading to the signal trasduction intiation. It is, therefore, reasonable that our current knowledge is only touching the surface of a remarkably intricate immune strategy.