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

Texenomycins are a family of linear lipopeptaibols with a long polyketide side chain at the N-terminus and 21 amino acid residues at the C-terminus, presenting demonstrated potential as antibiotics against plant fungal pathogens. In this study, texenomycins were identified and isolated from the fungus Mariannaea elegans strain TTI-0396 and showed effective antifungal properties against two plant pathogens Colletotrichum lagenarium and Botrytis cinerea. Through analysis of the whole-genome data of M. elegans 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 tex gene cluster that were proposed to be responsible for the biosynthesis of texenomycins and another related lipopeptaibol, lipohexin. The functions of six key genes (texQ, texO, texI, texG, texJ, and texV) in the hybrid PKS-NRPS system were verified by gene deletion experiments, and five genes (texQ, texO, texI, texG, and texV) were confirmed to be responsible for the biosynthesis of texenomycins, while four genes (texQ, texO, texI, and texJ) were involved in the biosynthesis of lipohexin. Furthermore, the function of one transcription factor gene (texR), which enhanced the production of texenomycins by regulating the key genes in the tex 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.