Most of the reported dominant disease-resistance genes in plants, R genes, encode NB-LRR immune receptors. Plant genomes carry many NB-LRR type R genes that recognize specific pathogens and induce resistance against them. Thus, this immune system in plants is thought to perform similar functions as the adaptive immune system in animals. In this review, we provide an overview of the resistance mechanisms, evolution, and agricultural applications of R genes against plant viruses. We also introduce recent advances in research into the regulatory mechanisms of R gene expression, focusing on regulation by microRNAs and introns. One of the most intriguing phenomena that occur following R gene-mediated recognition of viruses is programmed cell death around the initial infection site, although its significance in the survival strategies of plants remains to be elucidated. We discuss the possible benefits for plants of inducing such programmed cell death based on our empirical observations and some hypotheses from an ecological point of view.
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