Development of Arabidopsis thaliana transformants showing the self-recognition activity of Brassica rapa

Self-incompatibility in the Brassicaceae family is governed by two-linked highly polymorphic genes located at the S locus, SRK and SCR. Previously, the SRK and SCR genes of Arabidopsis lyrata were introduced into Arabidopsis thaliana transformants to generate self-incompatible lines. However, it has not been reported that the SRK and SCR genes of Brassica species confer self-incompatibility in A. thaliana. In this study, we attempted to construct self-incompatible A. thaliana transformants expressing the self-recognition activity of Brassica rapa by introducing the BrSCR gene along with a chimeric BrSRK gene (BrSRK chimera, in which the kinase domain of BrSRK was replaced with that of AlSKRb). We found that BrSRK chimera and BrSCR of B. rapa S-9 and S-46 haplotypes, but not those of S-29, S-44, and S-60 haplotypes, conferred self-recognition activity in A. thaliana. We also investigated the importance of amino acid residues involved in the BrSRK9-BrSCR9 interaction using A. thaliana transformants expressing mutant variants of BrSRK-9 chimera and BrSCR-9. The results showed that some of the amino acid residues are essential for self-recognition. The method developed in this study for the construction of self-incompatible A. thaliana transformants showing B. rapa self-recognition activity will be useful for analysis of self-recognition mechanisms in Brassicaceae.