Abstract
The evolution of selfing has been regarded as one of the most prevalent evolutionary transitions in flowering plants. The self-incompatibility (SI) system of Brassicaceae consists of male and female specificity genes at the S-locus (SCR/SP11 and SRK, respectively) and SI modifier genes. Despite many studies, the primary mutation responsible for the loss of SI in Arabidopsis thaliana still remained unknown. We found that a disruptive 213-bp inversion in the SCR gene is shared in 95% of European accessions, in contrast to the genome-wide polymorphism pattern. The interspecific crossings using Arabidopsis halleri as a pollen donor revealed that some accessions retain the female SI reaction, suggesting that all female components including SRK are still functional. Moreover, when the 213-bp inversion in SCR was inverted and expressed in transgenic plants, the functional SCR restored the SI reaction. These results indicate that the inversion within SCR is the first mutation disrupting SI. This is consistent with theoretical predictions, in that male mutations enjoy fitness advantages over female mutations because they can spread through both pollen and seeds.
