Efficacy and mechanisms of action of tick defensins against the phytopathogenic and toxinogenic fungus Fusarium graminearum

La fusariose de l’épi (FHB), principalement causée par le champignon Fusarium graminearum, est une maladie dévastatrice qui affecte les cultures céréalières et entraîne des pertes de rendement importantes et une diminution de la qualité des grains. En effet, F. graminearum produit des mycotoxines appelées trichothécènes de type B (TCTB) qui nuisent à la santé humaine et animale. Le peptide appelé TickCore3 (TC3), γ-core de la défensine de tique DefMT3, s’est avéré être un puissant antifongique contre F. graminearum et un inhibiteur efficace de la production de TCTB. Les déterminants structuraux et physico-chimiques nécessaires à l’efficacité du peptide ont été clarifiés. Des observations microscopiques ont permis de montrer que le peptide se fixait spécifiquement à l’enveloppe des spores fongiques. En outre, une stratégie associant transcriptomique (RNA-seq) et métabolomique (LC-MS/MS) a été mise en oeuvre pour décrypter le mécanisme d’action de TC3. Des changements importants dans le transcriptome de F. graminearum, comme dans son métabolome, ont été induits par une exposition au TC3 mettant en évidence un mécanisme à multiples facettes. Les résultats obtenus au cours de cette thèse ont démontré que TC3 était un candidat prometteur pour de nouvelles solutions de protection des végétaux, alternatives aux fongicides de synthèse.Fusarium Head Blight (FHB) mainly caused by the fungus Fusarium graminearum is a devastating disease affecting cereal crops that leads to significant yield losses and a reduced grain quality. Indeed, F. graminearum produces type B trichothecene mycotoxins (TCTB) which are detrimental to the health of humans and livestock. In the present study, a peptide referred to as TickCore3 (TC3), the γ-core of the tick defensin DefMT3, was demonstrated to be a potent fungicidal agent against F. graminearum and an efficient inhibitor of the production of TCTB. The structural and physico-chemical determinants required for the peptide efficacy were clarified. Through microscopic observation, the peptide was shown to bind specifically to the fungal spore’s envelope. Furthermore, a strategy combining transcriptomic (RNA-seq) and metabolomic (LC-MS) has been implemented to unravel the mechanism of action of TC3. Significant changes in F. graminearum transcriptome such as in its metabolome were induced by TC3 exposure evidencing a multi-faceted mechanism. The results obtained during this thesis demonstrated that TC3 could be a promising candidate for the development of new eco-friendly plant protection solutions

Efficacité et mécanismes d'action des défensines de tiques contre le champignon phytopathogène et toxinogène Fusarium graminearum

La fusariose de l’épi (FHB), principalement causée par le champignon Fusarium graminearum, est une maladie dévastatrice qui affecte les cultures céréalières et entraîne des pertes de rendement importantes et une diminution de la qualité des grains. En effet, F. graminearum produit des mycotoxines appelées trichothécènes de type B (TCTB) qui nuisent à la santé humaine et animale. Le peptide appelé TickCore3 (TC3), γ-core de la défensine de tique DefMT3, s’est avéré être un puissant antifongique contre F. graminearum et un inhibiteur efficace de la production de TCTB. Les déterminants structuraux et physico-chimiques nécessaires à l’efficacité du peptide ont été clarifiés. Des observations microscopiques ont permis de montrer que le peptide se fixait spécifiquement à l’enveloppe des spores fongiques. En outre, une stratégie associant transcriptomique (RNA-seq) et métabolomique (LC-MS/MS) a été mise en oeuvre pour décrypter le mécanisme d’action de TC3. Des changements importants dans le transcriptome de F. graminearum, comme dans son métabolome, ont été induits par une exposition au TC3 mettant en évidence un mécanisme à multiples facettes. Les résultats obtenus au cours de cette thèse ont démontré que TC3 était un candidat prometteur pour de nouvelles solutions de protection des végétaux, alternatives aux fongicides de synthèse.Fusarium Head Blight (FHB) mainly caused by the fungus Fusarium graminearum is a devastating disease affecting cereal crops that leads to significant yield losses and a reduced grain quality. Indeed, F. graminearum produces type B trichothecene mycotoxins (TCTB) which are detrimental to the health of humans and livestock. In the present study, a peptide referred to as TickCore3 (TC3), the γ-core of the tick defensin DefMT3, was demonstrated to be a potent fungicidal agent against F. graminearum and an efficient inhibitor of the production of TCTB. The structural and physico-chemical determinants required for the peptide efficacy were clarified. Through microscopic observation, the peptide was shown to bind specifically to the fungal spore’s envelope. Furthermore, a strategy combining transcriptomic (RNA-seq) and metabolomic (LC-MS) has been implemented to unravel the mechanism of action of TC3. Significant changes in F. graminearum transcriptome such as in its metabolome were induced by TC3 exposure evidencing a multi-faceted mechanism. The results obtained during this thesis demonstrated that TC3 could be a promising candidate for the development of new eco-friendly plant protection solutions

Efficacité et mécanismes d'action des défensines de tiques contre le champignon phytopathogène et toxinogène Fusarium graminearum

Fusarium Head Blight (FHB) mainly caused by the fungus Fusarium graminearum is a devastating disease affecting cereal crops that leads to significant yield losses and a reduced grain quality. Indeed, F. graminearum produces type B trichothecene mycotoxins (TCTB) which are detrimental to the health of humans and livestock. In the present study, a peptide referred to as TickCore3 (TC3), the γ-core of the tick defensin DefMT3, was demonstrated to be a potent fungicidal agent against F. graminearum and an efficient inhibitor of the production of TCTB. The structural and physico-chemical determinants required for the peptide efficacy were clarified. Through microscopic observation, the peptide was shown to bind specifically to the fungal spore’s envelope. Furthermore, a strategy combining transcriptomic (RNA-seq) and metabolomic (LC-MS) has been implemented to unravel the mechanism of action of TC3. Significant changes in F. graminearum transcriptome such as in its metabolome were induced by TC3 exposure evidencing a multi-faceted mechanism. The results obtained during this thesis demonstrated that TC3 could be a promising candidate for the development of new eco-friendly plant protection solutions.La fusariose de l’épi (FHB), principalement causée par le champignon Fusarium graminearum, est une maladie dévastatrice qui affecte les cultures céréalières et entraîne des pertes de rendement importantes et une diminution de la qualité des grains. En effet, F. graminearum produit des mycotoxines appelées trichothécènes de type B (TCTB) qui nuisent à la santé humaine et animale. Le peptide appelé TickCore3 (TC3), γ-core de la défensine de tique DefMT3, s’est avéré être un puissant antifongique contre F. graminearum et un inhibiteur efficace de la production de TCTB. Les déterminants structuraux et physico-chimiques nécessaires à l’efficacité du peptide ont été clarifiés. Des observations microscopiques ont permis de montrer que le peptide se fixait spécifiquement à l’enveloppe des spores fongiques. En outre, une stratégie associant transcriptomique (RNA-seq) et métabolomique (LC-MS/MS) a été mise en oeuvre pour décrypter le mécanisme d’action de TC3. Des changements importants dans le transcriptome de F. graminearum, comme dans son métabolome, ont été induits par une exposition au TC3 mettant en évidence un mécanisme à multiples facettes. Les résultats obtenus au cours de cette thèse ont démontré que TC3 était un candidat prometteur pour de nouvelles solutions de protection des végétaux, alternatives aux fongicides de synthèse

Use of Defensins to Develop Eco-Friendly Alternatives to Synthetic Fungicides to Control Phytopathogenic Fungi and Their Mycotoxins

International audienceCrops are threatened by numerous fungal diseases that can adversely affect the availability and quality of agricultural commodities. In addition, some of these fungal phytopathogens have the capacity to produce mycotoxins that pose a serious health threat to humans and livestock. To facilitate the transition towards sustainable environmentally friendly agriculture, there is an urgent need to develop innovative methods allowing a reduced use of synthetic fungicides while guaranteeing optimal yields and the safety of the harvests. Several defensins have been reported to display antifungal and even—despite being under-studied—antimycotoxin activities and could be promising natural molecules for the development of control strategies. This review analyses pioneering and recent work addressing the bioactivity of defensins towards fungal phytopathogens; the details of approximately 100 active defensins and defensin-like peptides occurring in plants, mammals, fungi and invertebrates are listed. Moreover, the multi-faceted mechanism of action employed by defensins, the opportunity to optimize large-scale production procedures such as their solubility, stability and toxicity to plants and mammals are discussed. Overall, the knowledge gathered within the present review strongly supports the bright future held by defensin-based plant protection solutions while pointing out the obstacles that still need to be overcome to translate defensin-based in vitro research findings into commercial products

Tick defensin γ-core reduces Fusarium graminearum growth and abrogates mycotoxins production with high efficiency

International audienceFusarium graminearum is a major fungal pathogen affecting crops of worldwide importance. F. graminearum produces type B trichothecene mycotoxins (TCTB), which are not fully eliminated during food and feed processing. Therefore, the best way to minimize TCTB contamination is to develop prevention strategies. Herein we show that treatment with the reduced form of the γ-core of the tick defensin DefMT3, referred to as TickCore3 (TC3), decreases F. graminearum growth and abrogates TCTB production. The oxidized form of TC3 loses antifungal activity, but retains anti-mycotoxin activity. Molecular dynamics show that TC3 is recruited by specific membrane phospholipids in F. graminearum and that membrane binding of the oxidized form of TC3 is unstable. Capping each of the three cysteine residues of TC3 with methyl groups reduces its inhibitory efficacy. Substitutions of the positively-charged residues lysine (Lys) 6 or arginine 7 by threonine had the highest and the lesser impact, respectively, on the anti-mycotoxin activity of TC3. We conclude that the binding of linear TC3 to F. graminearum membrane phospholipids is required for the antifungal activity of the reduced peptide. Besides, Lys6 appears essential for the anti-mycotoxin activity of the reduced peptide. Our results provide foundation for developing novel and environment-friendly strategies for controlling F. graminearum