MtHK1–LRP1 Gene Module for Engineering Biological Nitrogen Fixation
This genetic approach enables the targeted induction of root nodule structure in non-nodulated plants by introducing a specific gene module, MtHK1-LRP1, for inducing early nodule development. Nitrogen is a major limiting factor for plant growth and crop productivity. Although atmospheric nitrogen is abundant, most plants cannot utilize it directly and must rely on soil-based sources, typically through nitrate, ammonium, or organic nitrogen sources. However, only a small group of angiosperms has overcome this limitation by forming symbiotic nodules that house nitrogen-fixing bacteria, leaving most crops dependent on synthetic fertilizer. The global nitrogen fertilizer market reflects this unmet need, valued at approximately $128 billion in 2024, and is projected to reach $223 billion by 2034, growing at a 5.7% compound annual rate. Current approaches to reduce fertilizer dependence are limited by the narrow range of nodulating species and incomplete understanding of early nodule formation.
Researchers at the University of Florida have identified and functionally validated two key gene regulators, MtHK1, a histidine kinase, and LRP1, a member of the SHI/STY transcription factor family, for controlling the earliest stages of pericycle activation and nodule initiation. By inducing the expression of these genes in pericycle and/or cortex cells, it demonstrates nodule structures can form even in species that do not produce nodules, providing a new strategy for engineering nodule formation, a critical step toward biological nitrogen fixation, in agriculturally and commercially important plants
Application
Targeted activation of MtHK1 and LRP1 in cells to induce root nodule structures in plants for engineered biological nitrogen fixation
Advantages
- Identifies key genetic regulators (MtHK1 and LRP1) that control early pericycle activation during nodule initiation, enabling rational engineering of nodule development
- Triggers nodule formation without external cytokinin when MtHK1 and LRP1 are co-expressed, simplifying deployment across plant systems
- Induces nodule structures in plants that do not naturally form nodules, including Populus trichocarpa, expanding applicability to non-legume species
- Provides a modular gene construct approach for integration into crop improvement pipelines, targeting reduced fertilizer dependence
Technology
Researchers analyzed Medicago truncatula roots 24 hours after rhizobial inoculation using single-nuclei RNA sequencing, revealing two genes, MtHK1, a histidine kinase, and LRP1, a SHI/STY transcription factor, are key regulators of the early activation of pericycle cells during nodule initiation. RNA interference experiments showed plants form significantly fewer nodules when either MtHK1 or LRP1 is suppressed, demonstrating both genes are necessary for normal nodule development.
The MtHK1–LRP1 gene module is introduced into target plants using established transformation methods, with gene expression directed to specific root cell layers. These genes act as master regulators, activating the developmental pathway that leads to nodule formation, even in species that do not naturally produce nodules. When both genes are expressed together, nodule structures form without the need for external cytokinin, simplifying the process and broadening applicability. This approach offers a practical and scalable solution for enabling biological nitrogen fixation in crops previously unable to benefit from this trait.
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