Rgas

RGA stands for Resistance Gene Analog, a class of plant genes that resemble known disease resistance genes but may not themselves confer resistance. RGAs are typically identified by sequence similarity to R genes and by conserved motifs such as the NB-ARC/NB-ATP domain and leucine-rich repeats. They are often found in clusters and can be cataloged within the NBS-LRR (nucleotide-binding site-leucine-rich repeat) superfamily, including both TIR-NB-LRR (TNL) and CC-NB-LRR (CNL) types, as well as variants lacking some domains. Some RGAs carry additional domains, such as RPW8- or WRKY-like regions.

RGAs can act as precursors or decoys in the plant immune system. Although they may not themselves provide effective resistance, they represent a reservoir of genetic variation that can give rise to functional R genes through diversification, recombination, or expression changes. They contribute to defense signaling and can help plants sense pathogen effectors and activate immune responses.

Genomic distribution and evolution: RGAs occur throughout plant genomes, frequently in clusters. They evolve rapidly through gene duplication, unequal crossing over, and diversifying selection on their leucine-rich repeat regions, producing broad diversity in recognition specificity. Many RGAs exist as pseudogenes or truncated copies, yet their presence supports potential resistance across different genotypes and species.

Applications and research: In breeding and genomics, RGAs are used as markers for mapping resistance traits and as starting points for cloning functional R genes. Genome-wide identification of RGAs helps prioritize regions for resistance breeding and comparative studies, contributing to understanding how plants perceive pathogen attack and how resistance can be transferred or stacked in crops.