Characterization of the surfactin and fengycin-induced mechanisms involved in the protection of dicotyledons

Abstract

Surfactin (srf) and fengycin (fgc) are two of the cyclic lipopeptides (CLPs) produced by beneficial bacteria of the Bacillus genus. In the context of studying the biocontrol activity of these bacteria, the role of the two CLPs was investigated in this work. Literature mentions direct (pathogen antagonism) and indirect (plant defense elicitation) plant protection effect for these molecules. In this study, we first investigated their direct effect against fungal pathogens. While they are both known to be effective against various pathogens, only fgc, and not srf, displayed antifungal properties against Botrytis cinerea. Their effect on spore germination should, however, be further investigated. Then, their indirect effect was studied through quantification of early plant defense events such as calcium influx, Reactive Oxygen Species (ROS) production and extracellular medium alkalinization on Arabidopsis thaliana root protoplasts. Their effect was compared to those of chitin (cht) and flagellin (flg), two molecules of pathogenic origin able to elicit Pattern Triggered Immunity (PTI), a well-studied plant defense mechanism. No significant response could be observed after fgc treatments at concentrations between 2.5µM and 20µM. Srf, on the other hand, triggered calcium fluxes and ROS production. The results allowed to observe that srf does trigger early defense responses, but not in the same way as PTI elicitors. In addition, we observed that srf decreases the fluidity of the plant plasma membrane, supporting the hypothesis that the srf-membrane interaction may activate mechanosensitive ion channels, triggering early immune events.