Symbiotic peptides modulate rhizobial physiology without terminal differentiation
Bin Hu1,2, Robert Hänsch2,3,4, Kyra Grunau5
1Center of Molecular Ecophysiology (CMEP), College of Resources and Environment, Southwest University, Chongqing 400715, P.R. China.
Science Advances
|June 26, 2026
Summary
Perennial legumes use novel proline-glycine-rich peptides (NPGs) to manage symbiotic bacteria in root nodules. These peptides maintain bacterial function without terminal differentiation, supporting long-term nitrogen fixation.
Area of Science:
- Plant-microbe interactions
- Molecular biology
- Agricultural science
Background:
- Symbiotic nitrogen fixation is crucial for agriculture, reducing synthetic fertilizer needs.
- In legumes, rhizobia bacteria in root nodules differentiate into bacteroids, a process that can limit nodule lifespan.
- Perennial legumes require sustained symbiosis, which is incompatible with terminal bacteroid differentiation.
Purpose of the Study:
- To identify host factors regulating symbiont function in perennial legumes.
- To investigate alternative strategies for symbiont modulation in indeterminate nodules.
Main Methods:
- Identification and characterization of nodule-specific proline-glycine-rich peptides (NPGs) in *Robinia*.
- Analysis of NPG expression and localization within nodules.
- Assessing the impact of recombinant NPGs on *Mesorhizobium robiniae* physiology and gene expression.
Main Results:
- A novel family of nodule-specific proline-glycine-rich peptides (NPGs) was identified in *Robinia*.
- NPGs are highly expressed in nodules and accumulate in infected cells.
- Exposure to NPGs induced symbiotic gene expression in *Mesorhizobium robiniae* while preserving bacterial viability.
Conclusions:
- NPGs are identified as candidate host effectors in perennial legume symbiosis.
- These peptides represent an alternative mechanism for modulating symbionts, distinct from terminal differentiation.
- NPGs facilitate sustained nitrogen fixation in indeterminate nodules by maintaining bacterial function.
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