Parallel evolution of dominant pistil-side self-incompatibility suppressors in Arabidopsis.

Selfing is a frequent evolutionary trend in angiosperms, and is a suitable model for studying the recurrent patterns underlying adaptive evolution. Many plants avoid self-fertilization by physiological processes referred to as self-incompatibility (SI). In the Brassicaceae, direct and specific interactions between the male ligand SP11/SCR and the female receptor kinase SRK are required for the SI response. Although Arabidopsis thaliana acquired autogamy through loss of these genes, molecular evolution contributed to the spread of self-compatibility alleles requires further investigation. We show here that in this species, dominant SRK silencing genes have evolved at least twice. Different inverted repeat sequences were found in the relic SRK region of the Col-0 and C24 strains. Both types of inverted repeats suppress the functional SRK sequence in a dominant fashion with different target specificities. It is possible that these dominant suppressors of SI contributed to the rapid fixation of self-compatibility in A. thaliana.