Semipurified Rhamnolipid Mixes Protect Brassica napus Against Leptosphaeria maculans Early Infections.

The rapeseed crop (Brassica napus) has to cope with fungal diseases that significantly impacts yields. In particular, the fungal pathogen Leptosphaeria maculans, the causal agent of blackleg disease (also named Phoma stem canker), is a worldwide issue to this crop. Considering environmental concerns, it is essential to propose alternative natural compounds for rapeseed crop protection to reduce chemical fungicide use. Here we report data showing the efficacy of semipurified rhamnolipid (RL) mixes from bacterial origin to protect rapeseed against L. maculans at early stages of infection in controlled conditions. In addition, we show that RL solutions have excellent adhesion properties when sprayed onto rapeseed leaves, without adding any adjuvant. We demonstrate that RL mixes display direct antimycelial properties against the pathogen and stimulate plant defense responses in rapeseed. Our results validate, a preventive action of low RL concentrations to protect rapeseed against L. maculans and a curative effect in specific conditions when applied after the inoculation of the pathogen spores. Semipurified RL mixes therefore appear to be real cost-effective compounds that could be used in fields as biocontrol products to fight L. maculans early infections of rapeseed.

Exploring the Dual Interaction of Natural Rhamnolipids with Plant and Fungal Biomimetic Plasma Membranes through Biophysical Studies.

Rhamnolipids (RLs) are potential biocontrol agents for crop culture protection. Their mode of action has been proposed as dual, combining plant protection activation and antifungal activities. The present work focuses on the interaction of natural RLs with plant and fungi membrane models at the molecular scale. Representative models were constructed and the interaction with RLs was studied by Fourier transform infrared (FTIR) and deuterium nuclear magnetic resonance (²H NMR) spectroscopic measurements. Molecular dynamic (MD) simulations were performed to investigate RL insertion in lipid bilayers. Our results showed that the RLs fit into the membrane models and were located near the lipid phosphate group of the phospholipid bilayers, nearby phospholipid glycerol backbones. The results obtained with plant plasma membrane models suggest that the insertion of RLs inside the lipid bilayer did not significantly affect lipid dynamics. Oppositely, a clear fluidity increase of fungi membrane models was observed. This effect was related to the presence and the specific structure of ergosterol. The nature of the phytosterols could also influence the RL effect on plant plasma membrane destabilization. Subtle changes in lipid dynamics could then be linked with plant defense induction and the more drastic effects associated with fungal membrane destabilization.

Transcriptomic dataset from Arabidopsis thaliana seedlings in response to Pseudomonas aeruginosa mono-rhamnolipids.

The present data profile the large scale transcriptome changes in Arabidopsis thaliana Col-0 seedlings exposed to mono-rhamnolipids (Mono-RLs) from Pseudomonas aeruginosa secretome. Bacterial rhamnolipids (RLs) are biosurfactant known to trigger plant defense mechanisms and have a great potential for crop culture protection as environmental-friendly biocontrol solution. They are thought to interact directly with membrane lipids to induce plant defense gene expression and protection towards phytopathogens. However, to date, data on the global transcriptomic modifications induced by these natural amphiphilic glycolipids in plants are missing. Ten-day-old seedlings were treated for 1 or 3 h with 100 µM Mono-RLs in liquid growth medium for root absorption. Total RNA samples were extracted, purified, labelled and hybridized to Agilent V4 Gene Expression Microarrays 4 × 44 K (design ID 021169) carrying 43803 ssDNA probes of 60-mer covering the entire genome of A. thaliana. The dataset was validated by quality assessments including RNA sample quality, microarray quality and global gene expression profiling. The raw and normalized formats of these transcriptomic data are available via GEO repository with the accession number GSE168830. The dataset can be used to provide insights into the plant's early and later mechanisms induced or repressed by RLs. It can be compared to data obtained with other plant defense elicitors, including the well described compounds perceived by membrane protein receptors.

Rhamnolipids From Pseudomonas aeruginosa Are Elicitors Triggering Brassica napus Protection Against Botrytis cinerea Without Physiological Disorders.

Rhamnolipids (RLs) are amphiphilic molecules naturally produced by some bacteria with a large range of biological activities. Although some studies report their potential interest in plant protection, evaluation of their effects and efficiency on annual crops of worldwide agronomic interest is lacking. The main objective of this work was to investigate their elicitor and protective activities on rapeseed crop species while evaluating their physiological effects. Here we report that RLs from Pseudomonas aeruginosa secretome trigger an effective protection of Brassicanapus foliar tissues toward the fungus Botrytis cinerea involving the combination of plant defense activation and direct antimicrobial properties. We demonstrated their ability to activate canonical B.napus defense responses including reactive oxygen species production, expression of defense genes, along with callose deposits and stomatal closure as efficient physical protections. In addition, microscopic cell death observations and electrolyte leakage measurements indicated that RLs trigger a hypersensitive response-like defense in this plant. We also showed that foliar spray applications of RLs do not induce deleterious physiological consequences on plant growth or chlorophyll content and that RL protective properties are efficient on several grown cultivars of rapeseed. To our knowledge, this is the first report of RLs as an elicitor that suppresses fungal disease on tissues of an annual crop species under greenhouse conditions. Our results highlight the dual mode of action of these molecules exhibiting plant protection activation and antifungal activities and demonstrate their potential for crop cultures as environmental-friendly biocontrol solution.