Molecular insights into self-incompatibility systems:From evolution to breeding

Plants have evolved diverse self-incompatibility(SI)systems for outcrossing.Since Darwin’s time,consid-erable progress has been made toward elucidating this unrivaled reproductive innovation.Recent advances in interdisciplinary studies and applications of biotechnology have given rise to major break-throughs in understanding the molecular pathways that lead to SI,particularly the strikingly different SI mechanisms that operate in Solanaceae,Papaveraceae,Brassicaceae,and Primulaceae.These best-un-derstood SI systems,together with discoveries in other"nonmodel"SI taxa such as Poaceae,suggest a complex evolutionary trajectory of SI,with multiple independent origins and frequent and irreversible losses.Extensive exploration of self-/nonself-discrimination signaling cascades has revealed a compre-hensive catalog of male and female identity genes and modifier factors that control SI.Thesefindings also enable the characterization,validation,and manipulation of SI-related factors for crop improvement,helping to address the challenges associated with development of inbred lines.Here,we review current knowledge about the evolution of SI systems,summarize key achievements in the molecular basis of pol-len‒pistil interactions,discuss potential prospects for breeding of SI crops,and raise several unresolved questions that require further investigation.