R gene

Resistance genes (R-genes) are genes in plantgenomes that convey plant disease resistance against pathogens by producing R proteins. The main class of R-genes consist of a nucleotide binding domain (NB) and a leucine rich repeat (LRR) domain(s) and are often referred to as (NB-LRR) R-genes or NLRs. Generally, the NB domain binds either ATP/ADP or GTP/GDP. The LRR domain is often involved in protein-protein interactions as well as ligand binding. NB-LRR R-genes can be further subdivided into toll interleukin 1 receptor (TIR-NB-LRR) and coiled-coil (CC-NB-LRR).

Resistance can be conveyed through a number of mechanisms including:

• The R protein interacts directly with an Avr gene product of a pathogen (see Gene-for-gene relationship).
• The R protein guards another protein that detects degradation by an Avr gene (see guard hypothesis).
• The R protein may detect a pathogen-associated molecular pattern or PAMP (alternatively called MAMP for microbe-associated molecular pattern).
• The R protein encodes enzyme that degrades a toxin produced by a pathogen.

Once the R protein has detected the presence of a pathogen, the plant can mount a defence against the pathogen. Because R genes confer resistance against specific pathogens, it is possible to transfer an R gene from one plant to another and make a plant resistant to a particular pathogen.

Many plant resistance proteins are single-pass transmembrane proteins that belong to receptor kinases and toll-like receptors. R genes are of large interest in crop breeding, providing a large part of the immunity required by agricultural pathosystems.