Oxylipins are lipid-derived molecules that are ubiquitous in eukaryotes and whose functions in plant physiology have been widely reported. They appear to play a major role in plant immunity by orchestrating reactive oxygen species (ROS) and hormone-dependent signalling pathways. The present work focuses on the specific case of fatty acid hydroperoxides (HPOs). Although some studies report their potential use as exogenous biocontrol agents for plant protection, evaluation of their efficiency in planta is lacking and no information is available about their mechanism of action. In this work, the potential of 13(S)-hydroperoxyoctadeca-(9Z,11E)-dienoic acid (13-HPOD) and 13(S)-hydroperoxy-(9Z,11E,15Z)-octadecatrienoic acid (13-HPOT), as plant defence elicitors and the underlying mechanism of action are investigated. Arabidopsis thaliana leaf resistance to Botrytis cinerea was observed after root application with HPOs. They also activate early immunity-related defence responses, like ROS. As previous studies have demonstrated their ability to interact with plant plasma membranes (PPM), we have further investigated the effects of HPOs on biomimetic PPM structure using complementary biophysics tools. Results show that HPO insertion into PPM impacts its global structure without solubilizing it. Relationship between biological assays and biophysical analysis suggests that lipid amphiphilic elicitors that directly act on membrane lipids might trigger early plant defence events

Fatty acid hydroperoxides (HPOs) are amphiphilic molecules naturally produced by plants in stressed conditions and involved in plant immunity as signalling molecules. Although some studies report their potential use as exogenous biocontrol agents for plant protection, evaluation of their efficiency in planta is lacking and no information is available about their mechanism of action. In this work, the potential of two HPO forms, 13-HPOD and 13-HPOT, as plant defence elicitors and the underlying mechanism of action are investigated. Both HPOs trigger Arabidopsis innate immunity. They increase plant resistance to the pathogenic fungi Botrytis cinerea and activate early immunity-related defence responses, like ROS production. As our previous study has suggested that HPOs are able to interact with the plant plasma membrane (PPM) lipid fraction, we have further investigated the effects of HPOs on biomimetic PPM structure using complementary biophysics tools. Results show that HPO insertion into PPM impacts its global structure without solubilizing it. 13-HPOT, with an additional double bond compared to 13-HPOD, exerts a higher effect by fluidifying and reducing the thickness of the bilayer. Correlation between biological assays and biophysical analysis suggests that lipid amphiphilic elicitors that directly act on membrane lipids might trigger early plant defence events.