Plant defense compound disarms bacterial syringe

Scientists have discovered that erucamide, a plant-produced fatty acid amide, disrupts the function of the bacterial injectosome—a syringe-like nanomachine that some pathogenic bacteria use to help them infect their host (Science 2025, DOI: 10.1126/science.ads0377).

The injectosome, a multiprotein complex also known as the bacterial type III secretion system, helps bacteria deliver specialized proteins into host cells. These injected proteins then act to inhibit the host’s immune system. It’s a system employed by the common plant bacterial pathogen Pseudomonas syringae, and though many plants display some resistance to P. syringae, until now, the mechanism of that resistance was unclear.

The researchers identified erucamide from a crude leaf extract of Arabidopsis thaliana, a model organism for plant research, as the molecule responsible for immunity to P. syringae. Then they went several steps further to identify erucamide’s mode of action.

Corresponding author Xiaoguang Lei, a biochemist at Peking University, says in an email that erucamide binds to a pocket within the HrcC protein—a protein that forms a ring structure within the injectosome—and causes the whole assembly to break apart. The amide group, the position of the double bond, and the length of the alkyl chain all contribute to erucamide’s plant protection ability, according to a structural analysis included in the paper.

Scott Peck, a biochemist at the University of Missouri, says that the paper clears a high bar for plant pathology research by identifying the molecule responsible for immunity and uncovering how it works. He says this is especially significant because, within the field of plant pathology, “the low-hanging fruit has already been picked.”

And Lei adds that the research has several implications, noting that it “may help engineer crop plants with increased immunity against various bacterial pathogens,” and also “pave the way to develop new eco-friendly anti-bacterial pesticides.”

The paper explains that even when erucamide is applied exogenously to A. thaliana plants that have been modified to not produce the compound, it will restore immunity to P. syringae. Lei says that the research team is working on determining the viability of erucamide as a biopesticide and is “currently testing erucamide and its analogs in the fields.”

Even if erucamide and its analogs don’t pan out as viable pesticides, Peck says the research will still prove useful in developing other, new pesticides. “What they've done is really provided the basis for where new drug targets should be looking,” he says.