Blocking bacterial invasion: Erucamide inhibits the type III secretion system

The interaction between plants and pathogens is often described as an evolutionary arms race, in which plants develop multilayered immune signaling to counteract direct extracellular attacks and intracellular chemical effectors. The type III secretion system (T3SS) of Gram-negative bacteria serves as a key weapon, allowing pathogens to inject effectors directly into plant cells to suppress immune responses and promote infection. Although it is widely accepted that T3SS can be inhibited by plant immune signaling, the key determinants of this inhibition remain unknown. Miao and colleagues hypothesized that certain secondary metabolites may play a role in this inhibition. Using activity-guided chemical purification, they tested metabolites extracted through multiple rounds of organic solvent fractionation for their ability to inhibit secretion of the bacterial effector AvrPto in vitro. Notably, a methylene chloride fraction exhibited a strong inhibitory effect, and by using nuclear magnetic resonance and high-resolution mass spectrometry the active compound was identified as erucamide, a plant phytoalexin. Further investigation through homology modeling and mutant studies confirmed the specificity of this interaction; the authors speculate that erucamide might disrupt the assembly of the T3SS. This study clarifies the long-sought-after inhibitor of T3SS, highlights the critical function of erucamide, and lays the foundation for the development of novel pesticide strategies. (Summary by Ching Chan @ntnuchanlab) Science 10.1126/science.ads0377