Resistance gene complexes: Evolution and utilization

More than 30 genes have been characterized from different plant species tha t provide resistance to a variety of different pathogen and pest species. T he structures of most are consistent with a role in pathogen recognition an d defense response signaling. Resistance genes are very abundant in plant g enomes and most belong to tightly linked gene families. Evolution of R gene s is driven by selection on allelic variation created by mutation and re-as sorted by recombination between alleles and sometimes between different gen e family members. Selection favors genes that can recognize pathogen avr ge ne products that are present in pathogen populations. Selection at linked g ene families favors haplotypes with useful combinations of genes but a limi ted physiological cost to the plant. Future utilization of R genes will inc lude transfer between related genera and identification or construction of genes that condition durable resistance to variable pathogens. Genes with d urable resistance may interact with conserved pathogen elicitors or conditi on resistance responses that are independent of specific Avr gene interacti ons.