Mechanisms of plant resistance to viruses

Several models that describe plant–virus relationships have been proposed, including compatible and incompatible interactions.Plants contain resistance (R) genes, which confer resistance to pathogens, with each R gene conferring resistance to a particular pathogen. Several R genes have been cloned and some structure/function analyses performed.There are two current models for pathogen recognition by plant R proteins, which are the receptor–ligand model and the guard hypothesis.Several molecules and signalling pathways are induced upon pathogen recognition, and they cooperate to produce a defence response. Some of the best characterized molecules include salicylic acid, nitric oxide and reactive oxygen species, in addition to several plant hormones.RNA silencing is a highly conserved pathway in animals and plants that functions in development and in the maintenance of genome integrity. Plants have adapted this system for antiviral defence, and plant viruses have in turn developed mechanisms to suppress RNA silencing.The two pathways — RNA silencing and R-gene-mediated resistance — might interact to produce an effective defence response in plants.