Genome Mining Reveals Biosynthesis of the Antifungal Lipopeptaibols, Texenomycins, through a Hybrid PKS-NRPS System, in the Fungus <i>Mariannaea elegans</i>

Texenomycins are a family of linear lipopeptaibols with a long polyketide side chain at the N-terminus and 21 amino acid residues at the <i>C</i>-terminus, presenting demonstrated potential as antibiotics against plant fungal pathogens. In this study, texenomycins were identified and isolated from the fungus <i>Mariannaea elegans</i> strain TTI-0396 and showed effective antifungal properties against two plant pathogens <i>Colletotrichum lagenarium</i> and <i>Botrytis cinerea</i>. Through analysis of the whole-genome data of <i>M. elegans</i> strain TTI-0396, we discovered a hybrid PKS-NRPS system with the polyketide synthase (PKS: TexQ), thioesterase (TexO), acyl-CoA ligase (TexI), and three nonribosomal peptide synthetases (NRPSs: TexG, TexJ, TexV) in the <i>tex</i> gene cluster that were proposed to be responsible for the biosynthesis of texenomycins and another related lipopeptaibol, lipohexin. The functions of six key genes (<i>texQ</i>, <i>texO</i>, <i>texI</i>, <i>texG, texJ</i>, and <i>texV</i>) in the hybrid PKS-NRPS system were verified by gene deletion experiments, and five genes (<i>texQ</i>, <i>texO</i>, <i>texI</i>, <i>texG</i>, and <i>texV</i>) were confirmed to be responsible for the biosynthesis of texenomycins, while four genes (<i>texQ</i>, <i>texO</i>, <i>texI</i>, and <i>texJ</i>) were involved in the biosynthesis of lipohexin. Furthermore, the function of one transcription factor gene (<i>texR</i>), which enhanced the production of texenomycins by regulating the key genes in the <i>tex</i> gene cluster, was also demonstrated through gene deletion and overexpression experiments. Finally, a hypothetical scheme for texenomycins and lipohexin biosynthesis assembly is proposed. The elucidation of this intricate hybrid PKS-NRPS system has significantly deepened our comprehension of the mechanisms underlying the generation and chemical diversity of fungal lipopeptaibol natural products, offering a promising avenue for future research and potential applications in fungicidal disease control in agriculture.