The evolution of disease resistance genes

Several common themes have shaped the evolution of plant disease resistance genes. These include duplication events of progenitor resistance genes and further expansion to create clustered gene families. Variation can arise f rom both intragenic and intergenic recombination and gene conversion. Recom bination has also been implicated in the generation of novel resistance spe cificities. Resistance gene clusters appear to evolve more rapidly than oth er regions of the genome. In addition, domains believed to be involved in r ecognitional specificity, such as the leucine-rich repeat (LRR), are subjec t to adaptive selection. Transposable elements have been associated with so me resistance gene clusters, and may generate further variation at these co mplexes.