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Down-regulation of the mycotoxin beauvericin in a phytopathogen-endophyte interaction

Margot Bärenstrauch: Museum of Natural History

<div>The endophytic fungus <em>Paraconiothyrium variabile</em>, inhabiting the needles of the conifer <em>Cephalotaxus harringtonia</em>, is responsible for a strong decrease of beauvericin in <em>Fusarium oxysporum</em>, an ubiquitous soil-borne phytopathogen. The mycotoxin beauvericin provokes cell death in mammals and is supposed to be a virulence factor for phytopathogens. The reduction of beauvericin production is correlated to the formation of two oxylipins, 13-hydroperoxy-9,11-octadecadienoic acid (13-HpODE) and 13-keto-9,11-octadecadienoic acid (13-KODE) in the interaction zone between the two antagonists. Such oxidized fatty acids are known for their role in mycotoxin regulation and are synthetized by lipoxygenase (LOX) enzymes. Two <em>lox</em> genes are present in <em>P. variabile</em> (<em>pvlox1 and 2</em>) and <em>F. oxysporum</em> (<em>foxlox and foxlox1</em>) respectively. We emitted the hypothesis that endophytic oxylipins were inhibiting the transcription of the beauvericin synthetase gene (<em>beas</em>). qPCR results showed that the <em>foxlox </em>gene from <em>F. oxysporum</em> and the gene <em>pvlox2</em> from <em>P. variabile</em> were upregulated during the interaction, as well as the <em>beas</em> gene. These unexpected results indicate that the presence of the endophyte induces the <em>beas</em> gene of the phytopathogen, probably through an oxylipin signal. How can we then explain reduced beauvericin production during the interaction? Our hypothesis is that <em>P. variabile</em> hydrolyses beauvericin, as we have shown before for bacterial surfactins.</div>