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Triggering plants immune system with biorefined lignocellulosic molecules : effects on plant cell signaling and interaction with agro-pathogen Botrytis cinerea.

par Dardenne, Rodrigue
Président du jury Cannella, David
Promoteur Zarattini, Marco
Publication Non publié, 2023-08-14

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Résumé :

The plant cell wall is a dynamic structure mostly composed of high molecular weight polysaccharides such as cellulose. Its complex structure allows its structural integrity and functional properties such as protection towards abiotic and biotic stresses, e.g. heat stress and pathogens infection, thus participating in the plant immunity. Nevertheless, in order to reach the inside of the cells, bacterial and fungal pathogens have developed an arsenal of Cell Wall Degrading Enzymes (CWDEs) specialized in the degradation of the plant cell wall polymers such as cellulose. In reaction, plants have developed three main strategies for their immunity induction. One of them, defined as Damage-Triggered Immunity (DTI), consists in the recognition by plants of plant-derived molecules resulting from physical traumas or from their infection by pathogens, namely Damage-Associated Molecular Patterns (DAMPs). Cellooligosaccharides, represented by their native and oxidized counterpart (oxi)COS, are example of DAMPs resulting from the degradation of cellulose by a recently discovered class of CWDEs, referred to as Lytic Polysaccharide MOnooxygenases (LPMOs). Those LPMOs are classified into seven “Auxilary Activity (AA)” families with the expression of the AA9 family being particulary triggered during plants pathogenic attack by the necrotrophic fungus Botrytis cinerea, responsible for the grey mould disease. Moreover, (oxi)COS mixes have been recently proven to act as elicitors of plant immunity following their perception and signaling by the STRESS-INDUCED FACTORS 2 and 4 (SIF2 and SIF4). Therefore the use of (oxi)COS to trigger plant immunity could represent a valuable alternative to fungicides, especially in a current context of increased concerns towards public health and environmental hazards but also of economic interests since B.cinerea-induced production losses are estimated at up to $100 billion per year worldwide.The purposes of our work were thus to study the role of SIF2 and SIF4, and potentially of other genes, in plant immune response through the perception and signaling of (oxi)COS, better understanding the role of the BCIN_DELTALPMO9H AA9 LPMO from B.cinerea, as well as to conclude if the biostimulant activity of the (oxi)COS mix was the result of the addition of the individual eliciting potential of its components or came from their simultaneous synergic effect. We tested those assumptions notably through the symptomatology analysis of the three Col-0 wild type and sif2 and sif4 loss-of-function Arabidopsis thaliana strains treated with individual (oxi)COS and inoculated with the B05.10 WT and BcindeltaLPMO9H KO B.cinerea strains as well as through the emanation measurement over time of the stress-induced phytohormone Ethylene (ET) in Col-0, sif2 and sif4 KO plants treated with each individual (oxi)COS.From our results, we highlighted a possible obligatory synergy of some (oxi)COS for their eliciting potential on plant immunity with their perception and signaling being possibly either or both SIF2 and/or SIF4-dependent and possibly significantly impacted by their concentration. Moreover, following almost all (oxi)COS treatments, we noticed an increase of ET emanation in all Arabidopsis strains, thus highlighting a triggered immune response. Finally we suspected the BCIN_DELTALPMO9H to belong to the Type I or Type III AA9 LPMO. Nevertheless, our results being particularly contradictory, we concluded on the necessity of new trials to test for the relevance of our conclusions.