R Gene and its Role in Disease Managements in Plants

Many disease resistance (R) proteins of plants detect the presence of disease-causing bacteria, viruses, or fungi by recognizing specific pathogen effector molecules that are produced during the infection process. Effectors are often pathogen proteins that probably evolved to subvert various host processes for promotion of the pathogen life cycle. Five classes of effector-specific R proteins are known, and their sequences suggest roles in both effector recognition and signal transduction. The most prevalent class of R proteins contain leucine-rich repeats (LRRs), a central nucleotide binding site and a variable amino terminal domain. Other classes possess an extracellular LRR domain, a transmembrane domain and sometimes an intracellular serine/threonine kinase domain. R proteins function in pathogen perception and/or the activation of conserved defence signalling networks. Upon infection, specific effectors produced by pathogens and presumed to promote growth in host tissue, are either directly recognized by different R proteins or are recognized by a targeted plant protein which is itself guarded by R proteins.