Resistance Genes ( R Genes) in Plants

Abstract

Abstract The activation of plant defence to restrict pathogen invasion is often conferred by resistance (R) proteins. 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. Subsequently, various defence signalling networks are activated via R protein phosphorylation, oligomerization, degradation, conformational changes and by the shuttling of R proteins between the plant cell cytoplasm and the nucleus. The overall outcome is dramatic cellular reprogramming and the activation of coordinated defence responses both locally at the site of infection as well as systemically throughout the plant. Many R gene loci appear to be under positive genetic selection, which rapidly diversifies paralogous sequences. Some R genes are present in plant genomes at single loci as either a single sequence or an allelic series whilst others reside within tight or loose clusters of related R sequences. For a century, plant breeders have genetically characterized and used R genes to reduce the impact of pathogens on crop production. More recently, various transgenic approaches have been tested to provide broader spectrum control and improved durability.