Evidence for orthologous S-Locus-Related I genes in several genera of Brassicaceae

In the Brassica genus, self-incompatibility (SI) is considered to be controlled by the combined action of several highly polymorphic genes located at the S-locus. These genes, including the S-Locus Gene (SLG), and the S-Receptor Kinase (SRK) are all members of the complex multigenic S-family. The S-Locus Related I gene (SLR1) is a member of the S-family, but is not involved in SI control since it is not linked to the S-locus and is essentially monomorphic. Here we confirm or demonstrate the occurrence of SLR1 as highly diverged but not very polymorphic genes in several genera of the Brassicaceae family (Arabidopsis, Brassica, Hirschfeldia, Raphanus, Sinapis). They show similar expression patterns with respect to location (stigmatic papillae), developmental stage (before and during anthesis) and transcript size (1.6 kb). In addition, they are assumed to be involved in the same biological function (late pollen adhesion). These features suggest that the pollen adhesion function might have evolved towards self-pollen recognition through duplication of SLR1 and recruitment of a protein kinase gene.