Understanding and harnessing unreduced gametes for crop improvement

Unreduced gametes (UGs), also known as 2n gametes, retain the somatic chromosome number and represent a fundamental mechanism for sympatric polyploidization in plants. In common wheat (Triticum aestivum L.) and its triticeae relatives, UGs are not only instrumental in species evolution but may also serve as a powerful tool for modern crop improvement. This review synthesizes progress in understanding the cytological and genetic foundations of UG formation in plants, which primarily arises through meiotic restitution events. The achievements made so far in the exploitation of UGs are detailed, which suggest that appropriate manipulation of UGs has potentials in revolutionizing crop breeding, facilitating de novo synthesis of polyploids, enabling challenging wide hybridizations, and permitting direct introgression of valuable traits from wild relatives into cultivated backgrounds. To fully realize these potentials, there are still many biological and technical hurdles to overcome. We outline the major challenges and propose research directions for further basic and applied studies on UGs, which include elucidating the molecular mechanisms underpinning UG formation, raising the efficiency of UG induction, and integrating UG-based technology with crop genomics and advanced breeding pipelines. Breakthroughs in these areas of research will help to promote a new chapter of crop improvement through enhancing genetic diversities, cultivar innovation, and resilient production of crops in the face of worsening global climate change.