Plant Resistance to Viruses: Natural Resistance Associated with Dominant Genes

Abstract

Plant resistance to pathogens is often controlled by dominant disease resistance (R) genes. R-gene-mediated resistance is dependent on the pathogen possessing a matching avirulence (Avr) gene. This phenomenon is known as gene-for-gene resistance, and has been shown to act against a number of pathogen types including viruses. R genes encode a small number of different protein classes. The most prevalent, and the only type shown to date to recognize viruses, are known as NB-LRR proteins because they contain nucleotide-binding (NB) and leucine-rich repeat (LRR) domains. Plant genomes possess large numbers of NB-LRR encoding genes that are highly variable between species and, often, within species. A number of different viral proteins have been shown to act as Avr determinants. R genes can mediate different responses depending on the viral isolate, genetic background of the host, or environmental conditions. These range from extreme resistance, with no visible response, to the hypersensitive response, which results in necrotic lesions at the site of infection, to systemic necrosis, where cell death spreads throughout the plant. Recent progress has identified a number of proteins and small molecules in these processes.