Natural Plant Peptide Found to Protect Plants from Several Destructive Fungal Pathogens

The Science

A bacterium, living within nitrogen-fixing nodules in the roots of the model legume plant Medicago truncatula (alfalfa), converts atmospheric nitrogen gas into forms that the plant can absorb and use. The plant controls this nitrogen-fixing process by producing nodule-specific cysteine-rich (NCR) peptides. M. truncatula secretes about 700 different NCR peptides, many of which possess antimicrobial properties. To learn how the structure of these NCR peptides relates to antimicrobial activity, a team of scientists solved the first three-dimensional (3D) structure of an NCR peptide, NCR044.

The Impact

Pre- and postharvest fungal diseases cause substantial losses in the yields of many important crops. Multiple applications of chemical fungicides can mitigate diseases, but these products become ineffective over time because the fungal species becomes more resistant to the fungicide. Peptide-based antifungal agents are an environmentally friendly alternative to chemical fungicides. Tobacco and tomato plants, as well as lettuce leaves and rose petals, sprayed with this peptide resisted gray mold disease caused by the fungus Botrytis cinerea.

Summary

Researchers solved the first three-dimensional3D structure of aN nodule-specific cysteine-richNCR peptide, NCR044, which is from a legume plant Medicago truncatula. They also uncovered its mechanism of action in protecting the crops against the fungal pathogen B. cinerea, which damages many economically important crops such as tomato, grape, and strawberry. To identify this structure, researchers used multi-dimensional nuclear magnetic resonance spectroscopy, as part of the Functional Omics Integrated Research Platform at EMSL, the Environmental Molecular Sciences Laboratory (EMSL). This analysis revealed a largely disordered, and presumably dynamic, peptide structure containing a short anti-parallel β-sheet, tiny α-helix, and, when oxidized, two stabilizing disulfide bonds.

The peptide NCR044 exhibited antifungal activity against several plant fungal pathogens at low micromolar concentrations. The researchers identified several mechanisms of action, including membrane disruption and the induced production of reactive oxygen species that triggers fungal cell death. Confocal and super- resolution microscopy revealed that the peptide localizes near fungal cell walls, then diffuses throughout the fungal cell and localized in the nucleolus where ribosomal assembly takes place. These findings highlight novel antifungal activity associated with nodule- specific cysteine-rich peptides from legumes and pave the way for future development of these peptides as antifungal agents.

Principal Investigator(s)

Dilip Shah
Donald Danforth Plant Science Center
[email protected]

Garry Buchko
Pacific Northwest National Laboratory
[email protected]

Funding

This work was supported by TechAccel, a National Science Foundation Major Research Instrumentation grant, and the Advanced Bioimaging Laboratory at the Danforth Plant Science Center. The structure for this peptide was solved using resources at the Environmental Molecular Sciences Laboratory (EMSL), a U.S. Department of Energy Office of Science User Ffacility, with support from the Office of Science’s Office of Biological and Environmental Research.

References

Velivelli, S.L.S., Czymmek, K.J., Li, H., Shaw, J.B., Buchko, G.W., Shah, D.M et al. “Antifungal symbiotic peptide NCR044 exhibits unique structure and multi-faceted mechanisms of action that confer plant protection.” Proceedings of the National Academy of Science USA 117(27), 16043–16054 (in press, (2020). [DOI:10.1073/pnas.2003526117] OSTI ID: 1635223