Dominance hierarchy arising from the evolution of a complex small RNA regulatory network

Self-pollen rejection in the Brassicaceae is determined by the diploid genotype of the pollen-producing plant, and it has long been known that the alleles show a dominance hierarchy. How this hierarchy is controlled and evolves has been a classical puzzle since the pre-molecular days of genetics. Here, we uncover the system of at least 17 small RNA (sRNA) producing loci and their multiple target sites that collectively control the dominance hierarchy among alleles of a self-incompatible Arabidopsis species. Our results demonstrate that natural selection shapes a dynamic repertoire of sRNA/targets interactions by jointly acting on sRNA genes, their processing precision and their target sites. It is remarkable that a single gene can evolve such a complex system of regulation among its own alleles. Overall design: Sequencing of small RNAs from A. halleri floral buds, with this single exception (Al14, from A. lyrata).