Abstract
Most of the known R-genes are considered to be functioning by specifically recognizing the corresponding Avr-gene product of pathogen. However, the mechanism of their diversification, which is vital for their function, as in the case of immunoglobulins of vertebrates, because of the wide variety and rapidly mutating pathogen's genes, is not known and simply presumed to be due to recombination of clustered R-genes. We noticed a hyper-variable region around the rice blast resistance gene Pi-b, which was identified by us as an isolated R-gene. This tendency was confirmed in several R-genes in Arabidopsis by comparing accessions Columbia and Landsberg, although some was not so highly variable. By comparing 10 accessions, we have confirmed that this variation is not of the biallelic character, and propose a selection process after the development of new variation in hypervariable regions.
