From recognition to response: integrated signaling pathways determining pollen acceptance and rejection in...

Generation of competent offspring is vital for the prosperity of flowering plants. The pistil not only functions as a conduit for pollen tubes to grow to the ovary but also provides a selective venue for facilitating the growth of compatible pollen tubes and discouraging invaders and incompatible pollen. This review integrates recent advances in pollen-pistil interactions on dry stigmas of the Brassicaceae in the domains of self-incompatibility (SI) and cross-compatibility. We first outline the initial recognition mechanisms that distinguish self from nonself pollen and then highlight how key stigma responses are differentially regulated during compatible and incompatible responses, including calcium signaling, exocytosis, cytoskeleton dynamics, reactive oxygen species, aquaporin activity, and cell wall permeability. By linking these discrete cellular events to their physiological outcomes, we provide a unified framework for understanding how Brassicaceae stigmas precisely control fertilization. A deeper understanding of these mechanisms also informs new strategies for improving crop breeding in economically important Brassicaceae species, which widely use SI to produce F1 hybrid seeds.