Characterization of oxylipin signaling in the chemical interaction between the endophyte Paraconiothyrium variabile and the phytopathogen Fusarium oxysporum

Abstract : Endophytic fungi are non-pathogenic microorganisms involved in mutualistic associations with their host. Foliar endophytes, in particular, represent a very diverse group but little is known about their interactions with the host and its associated micro-organisms. In preliminary work, exploring the leaf microbial diversity of the conifer Cephalotaxus harringtonia, our team isolated the fungal strain Paraconiothyrium variabile (Ascomycota), an antagonist of the phytopathogen Fusarium oxysporum. During their interaction, decreased amounts of the F. oxysporum mycotoxin beauvericin, and higher amounts of the two oxylipins, 13-hydroperoxyoctadecadienoic acid (13-HPODE) and 13-oxo-octadecadienoic acid (13-oxo-ODE), were observed in the confrontation zone. The objective of the present work was to understand the mechanisms leading to beauvericin decrease during the interaction and to explore the role of oxylipins in beauvericin regulation. In my thesis work I show the presence of two lox genes in P. variabile (pvlox1 and pvlox2) coding both for manganese lipoxygenases, potentially at the origin of 13-HPODE and 13-oxo-ODE. Pvlox2 is specifically induced during the interaction, which lead to an increased synthesis of 13-HPODE in P. variabile. The endophyte itself, as well as the oxylipin 13-HPODE, up-regulated the beauvericin biosynthesis gene beas, which was paralleled by higher mycotoxin content in the mycelium of F. oxysporum. Finally, we showed that beauvericin inhibited the endophyte’s growth, but the latter was capable to degrade the mycotoxin, which explains the lower amounts of beauvericin found in the competition zone. This work presents pioneer undertaking to elucidate the role of oxylipins in inter-microbial crosstalk.
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Margot Barenstrauch. Characterization of oxylipin signaling in the chemical interaction between the endophyte Paraconiothyrium variabile and the phytopathogen Fusarium oxysporum. Microbiology and Parasitology. Museum national d'histoire naturelle - MNHN PARIS, 2018. English. ⟨NNT : 2018MNHN0010⟩. ⟨tel-02014160⟩

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