Azelaic acid key to plant immunity

A common plant metabolite used in creams to treat acne and rosacea has a major role in priming plants’ systemic immune system, US researchers have found.

Azelaic acid has antibacterial and anti-inflammatory properties and is commonly used in dermatological applications in humans.

Now, it has been identified as a signalling weapon in Arabidopsis to prime the plants to accumulate salicylic acid upon infection.

Salicylic acid, which is also used popularly in skin treatments, is a phytohormone in plants which plays a role in pathogen resistance. It is highly active in systemic acquired resistance (SAR) in plants, in which resistance to localised infections develops as a means of mounting a stronger defense upon secondary infection.

SAR involves infected leaves developing a sap called petiole exudate, which is then sent through the vascular system to confer resistance to uninfected leaves.

The US team, led by Ho Won Jung and Jean Greenberg from the University of Chicago, used gas chromatography and mass spectrometry to look for metabolites that were highly active in SAR-induced exudates.

They found levels of azelaic acid were six-fold higher in active compared with non-active exudates.

Using a strain of Psuedomonas syringae, they found applying the acid directly to leaves conferred both local and systemic resistance, but it did not seem to directly inhibit the pathogen.

What it did was increase salicylic acid accumulation. It also induced a protein they have called azelaic acid induced 1 (AZI1), which confers disease resistance when overexpressed. They found that this protein modulates the production or translocation of a mobile signal during systemic acquired resistance.

Azelaic acid is found in many plants, including wheat, rye and barley, so the researchers are investigating its potential as a topical treatment for crops.

Their paper is published in Science.