Engineered diazotrophs with host-inducible nitrogen supply systems: Transforming rice farming through innovative...

Nitrogen pollution represents a critical challenge in the 21st century, highlighting the urgent need for sustainable alternatives to industrial nitrogen fixation. Diazotrophic bacteria, which uniquely convert dinitrogen (N₂) into bioavailable forms, offer a promising solution through biological nitrogen fixation (BNF). These bacteria typically perform nitrogen fixation under nitrogen-limited conditions. Over the past 50 years, extensive research has elucidated the molecular mechanisms and regulatory pathways governing BNF. Recent microbiome studies have revealed that wild rice accessions harbor a greater abundance of diazotrophic bacteria, whereas a substantial proportion of these beneficial microbes have been lost in modern cultivated varieties. Advancements in synthetic biology have enabled the engineering of nitrogen‑exporting diazotrophs, potentially reducing dependence on industrial nitrogen fertilizers. This review emphasizes the importance of targeted research to develop customized diazotrophic microbes in conjunction with synthetic microbial community that can serve as nitrogen exporters for rice. Furthermore, it highlights the necessity of identifying rice cultivars that are particularly responsive to these microbial interventions. Finally, it provides a comprehensive roadmap addressing key challenges and opportunities in deploying BNF to supplement plant nitrogen nutrition and advance sustainable agriculture.