Carbon-11 Azelaic Acid as a Signaling Molecule for Mechanistic Studies in Plants

The Science

When a pathogen attacks a plant, the plant mounts an immune response that alerts the rest of the plant, a response called systemic acquired resistance (SAR). The chemical compound(s) responsible for inducing the immunity is a topic of intense interest for agriculture, including for bioenergy crops. For example, the application of a 9-carbon-atom-chain (C-9) dicarboxylic acid, azaleic acid, induces immunity, but the similar C-8 and C-10 diacids do not. One hypothesis is that the azaleic acid, but not the related acids, moves to distant parts of the plant. New radiochemistry imaging research at Brookhaven National Laboratory has developed a rapid method to label these three acids with Carbon-11 (¹¹C, half-life of 20.4 min) for short-term (minutes to hours) tracking of their movement within the plant, and with Carbon-14 (¹⁴C, half-life of 5730 years) for long-term (hours to days) studies. When applied to a leaf, [¹¹C]-azaleic acid shows substantial movement within an hour. When [¹⁴C]-azaleic acid is applied to the roots, it distributes throughout the whole plant within a day. These studies demonstrate that azaleic acid has the potential to be a mobile signaling molecule. The radioactive-carbon labeled diacids will have utility as scientific tools to unravel SAR mechanisms and other phenomena that impact production of robust bioenergy crops.

Summary

Systemic acquired resistance (SAR), a highly desirable form of plant defense, provides broad-spectrum immunity against diverse pathogens. The recent identification of seemingly unrelated chemical inducers of SAR warrants an investigation of their mutual interrelationships. Researchers show that SAR induced by the dicarboxylic acid azelaic acid (AA) requires the phosphorylated sugar derivative glycerol-3-phosphate (G3P). Pathogen inoculation induced the release of free unsaturated fatty acids (FAs) and thereby triggered AA accumulation, because these FAs serve as precursors for AA.

BER Program Manager

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]

References

Yu, K., J. M. Soares, M. K. Mandal, C. Wang, B. Chanda, A. N. Gifford, J. S. Fowler, D. Navarre, A. Kachroo, and P. Kachroo. 2013. “A Feedback Regulatory Loop Between G3P and Lipid Transfer Proteins DIR1 and AZI1 Mediates Azelaic-Acid-Induced Systemic Immunity,” Cell Reports 3, 1266–78. DOI: 10.1016/j.celrep.2013.03.030. (Reference link)

Best, M., A. N. Gifford, S. W. Kim, B. Babst, M. Piel, F. Roesch, J. S. Fowler. 2012. “Rapid Radiosynthesis of [¹¹C] and [¹⁴C]Azaleic, Suberic, and Sebacic Acids for in vivo Mechanistic Studies of Systemic Acquired Resistance in Plants,” Journal of Labelled Compounds and Radiopharmaceuticals 55, 39-43. DOI: 10.1002/jlcr.1951.