Pan-family pollen signals control an interspecific stigma barrier across Brassicaceae species.

Abstract

Prezygotic interspecific incompatibility prevents hybridization between species, which limits interbreeding strategies for crop improvement using wild relatives. The <i>Brassica rapa</i> female self-incompatibility determinant, <i>S</i>-locus receptor kinase (SRK), recognizes interspecific pollen. Here, we report the discovery of a pan-Brassicaceae SRK-interacting interspecific pollen signal (SIPS). On <i>B. rapa</i> stigmas, SIPSs from <i>Arabidopsis</i> and other Brassicaceae species target <i>Br</i>SRK and recruit the female fertility regulator FERONIA receptor kinase to increase stigmatic reactive oxygen species and reduce interspecific pollen viability. <i>Arabidopsis thaliana sips</i> mutant pollen failed to trigger interspecific incompatibility responses. Unlike self-incompatibility, which is controlled by the polymorphic <i>S</i> locus, different genetic variants of SRK interacted comparably with SIPS. This study establishes SIPS-SRK as a Brassicaceae-specific ligand-receptor pair that broadly maintains the stigmatic interspecific barrier in self-incompatible species.