Developing an Efficient System for Hybrid Rice Seed Production Using Partial Male Sterility

Efficient production of hybrid rice seeds requires male sterility systems to overcome the challenges of self-pollination. In this study, we identified male gametic transfer defect (GTrD)5 and GTrD9 as essential genes for the process of male gamete transmission in rice. Mutations in these genes cause partial male sterility by impairing pollen tube elongation, thereby reducing the fertilisation rate. Using CRISPR/Cas9 technology, we developed gtrd5flo5 and gtrd9flo5 double mutants that combined the gtrd5 and gtrd9 genes responsible for partial male sterility with the floury endosperm (FLO)5 gene, whose defects result in seeds with an opaque endosperm, allowing us to easily differentiate between hybrid and self-pollinated seeds. This two-line hybrid system demonstrated a high rate of hybrid seed production with significantly reduced self-pollination ratios. The hybrid seeds resulted in plants with increased height, panicle size and grain yield compared with those obtained from the parental lines and also displayed heterosis. Unlike the current two-line hybrid systems based on photoperiod- and thermosensitive genic male-sterile lines, our approach is independent of environmental factors, ensuring a stable and reliable hybrid seed production. This novel method simplifies seed production, enhances efficiency and offers a cost-effective and environmentally sustainable solution for hybrid rice breeding.