Fonds Spéciaux de la Recherche (Gx-ABT-ULg)
Title : ”Biophysical study of the plant immunity triggered by lipopeptides”
Promotors: Magali Deleu, Laurence Lins
There is nowadays an increasing demand from consumers, farmers and authorities for sustainable and eco-friendly strategies to combat plant diseases. In this context, biological control through the use of natural antagonistic microorganisms has emerged as a promising alternative to reduce the use of chemical pesticides. Some species of the Pseudomonas and Bacillus genera are among the most efficient biocontrol bacteria notably due to their natural soil fitness but also to their huge potential to produce a range of antibiotic compounds allowing direct antagonism of plant pathogens. Moreover, some of their metabolites act indirectly to inhibit pathogens by stimulating some immune responses in the host plant leading to an enhanced resistance state less susceptible to subsequent attack. This immunostimulation phenomenon is an important component of the global biocontrol activity of some beneficial rhizobacteria since it is long-lasting and is usually expressed systemically in the host (induced systemic resistance (ISR)). However, from a fundamental point of view, molecular events underlying ISR are considerably less well understood than in the case of pathogen-triggered plant immunity, notably regarding the nature of the elicitors produced by rhizobacteria and the way they are perceived by plant cells. In that context, recent works shed new light into the mechanism of perception of the surfactin-type lipopeptide (CLP) playing a key role as ISR elicitor secreted by Bacillus. In collaboration with Dr. M. Ongena (CWBI), it was shown that interaction of the CLP, notably surfactin, with membrane lipids is crucial for elicitor activity.
This project aims at combining experimental/in silico biophysical studies to decipher the molecular mechanisms responsible for perception of surfactin at the plasma membrane of root cells. These biophysical aspects will be put in parallel to biological approaches carried out in the context of a recently granted multidisciplinary ARC project (FIELD). The first line of biophysical experiments with purified root PM as well as the proteomic studies will involve both tobacco and Arabidopsis in order to not restrict our conclusions to one species. However, further functional studies will be mainly performed using Arabidopsis as model host plant since it offers not only the best knowledge on immune-related molecular network and corresponding genes necessary for transcriptomic studies but also the highest panoply of functional mutants.
One original aspect of our project is to test the effects of temperature on the lipopeptide/membrane interaction, since chilling conditions for plants may clearly affect the physical state of their PM. It could therefore influence the interaction with the elicitor as we showed enhanced binding to highly ordered lipid bilayers compared to a more fluid physical state enriched in unsaturated lipid chains. At low T°, membranes are actually more rigid. Plants hence react to coldness by increasing the proportion of unsaturated fatty acids in their membranes to compensate for such loss in fluidity essential for proper functioning. The outcome of the interaction of lipopeptides with PM of chilled plants could therefore be strongly affected. We intend to check this hypothesis by using the biophysical tools such as FTIR spectroscopy and further testing via functional ISR assays by using cold-acclimated plants.