When no means no: guide to Brassicaceae self-incompatibility

More than half of the flowering plants have a sophisticated mechanism for self-pollen rejection, named self-incompatibility (SI). In Brassicaceae, recognition specificity is achieved by the interaction of the stigmatic S-RECEPTOR KINASE (SRK) and its ligand S-LOCUS CYSTEINE-RICH PROTEIN (SCR). Recent years have seen significant advances in understanding the SI response. Progress has been made on elucidating the regulation and function of proteins that act as either molecular partners of SRK or modulators of SI. Thus, modules controlling the specificity of the central receptor–ligand interaction have been identified on both SRK and SCR proteins. A role for intracellular protein trafficking in SI has also been demonstrated. Here, we integrate the novel findings into the existing model to present the current understanding of SI signaling.