Evaluation of the impact of structural changes on the plant immunization potential of surfactin

Abstract

The cyclic lipopeptide (CLP) surfactin is secreted by Bacillus spp. such as Bacillus velezensis, a plant growth promoting rhizobacteria (PGPR). This molecule has biological functions among which the ability to stimulate the induced systemic resistance (ISR) in several plant models. This phenomenon could be part of the transition to sustainable agriculture since it can help the plant to face many pathogens infections. However, the molecular basis of ISR induction by surfactin is still poorly understood. In this context, a structure-activity approach of surfactin has been adopted to get deeper insights into the relation between this CLP and ISR . Thus, the aim of this thesis is to evaluate the impact of structural changes in the plant immunization potential of surfactin. For this purpose, naturally occurring variants of surfactin, pumilacidin and lichenysin, have been chosen. These CLPs vary in fatty acid chain length and in peptide composition. In order to deepen our knowledge in the induction of ISR in planta, the reactive oxygen species (ROS) burst and the stimulation of the transcriptional factor MYB72, two plant immunity markers, have been studied. To achieve these objectives, surfactin, pumilacidin and lichenysin have been produced and purified in order to test their ability to trigger ROS burst and myb72 stimulation in addition to their activity as ISR elicitors in Arabidopsis thaliana L. (Arabidopsis), the plant model used in this study. In this work, we firstly demonstrate that the structure of surfactin is determinant for ISR induction in Arabidopsis. Then, regarding ISR markers, our results suggest that myb72 could be an interesting ISR marker where ROS burst alone is not sufficient to trigger ISR. Moreover, we prove that the change of one single amino acid in the peptide ring of the CLP can alter the activity of surfactin. Furthermore, this work provides new insight into ISR induction and in particular on the role of the enzyme, β-glucosidase BGLU42 in relation to myb72.