Two gene clusters are required for mannosylerythritol lipid biosynthesis in <i>Sporisorium reilianum</i>

Mannosylerythritol lipids (MELs) are antibacterial surface-active molecules produced by several basidiomycetous fungi. Enzymes for MEL biosynthesis are encoded in a gene cluster composed of five genes, which are both necessary and sufficient for the biosynthesis of MELs. Here, we report that in two closely related biotrophic pathogens<i>-Sporisorium reilianum f. sp. reilianum</i> (<i>SrS</i>) and <i>Sporisorium reilianum SRZ2</i>-MEL production is achieved through the combined activity of two gene clusters. While the larger cluster is required for production of the disaccharide moiety, for attachment of one acyl chain to the sugar backbone and for export of MELs, the smaller cluster encodes two enzymes for additional acylation of the sugar backbone and is essential to produce mature MELs in <i>S. reilianum</i>. The genes in the smaller cluster appear to be duplications of two of the original genes in the larger cluster, which are not expressed in <i>SrS</i> but in related fungi, e.g., <i>Ustilago maydis</i>. MELs made by <i>SrS</i> are tri-acylated and exhibit altered physical and chemical properties, making them interesting candidates for future biotechnological and pharmaceutical applications. In summary, our study showcases how duplication and diversification of MEL clusters can lead to the evolution of novel biosurfactants.IMPORTANCESecondary metabolites produced by fungi can act as weapons against competitors, can help access nutrients, or assist development and communication. One group of secondary metabolites are surface-active glycolipids that have a great potential as biodegradable detergents. Upon nitrogen starvation, biosynthesis of the glycolipid mannosylerythritol lipid (MEL) is induced by a gene cluster composed of five genes in the plant pathogen <i>Ustilago maydis</i> and related basidiomycetous fungi. This study shows that in the smut fungus <i>Sporisorium reilianum f. sp. reilianum,</i> the five genes of the MEL gene cluster were not sufficient to produce the isolated MEL variant. In contrast to conventional MELs, MELs of <i>S. reilianum</i> are tri-acylated at the mannose moiety with acyl groups in the range of C₆-C₁₀. These MELs exhibit altered physical and chemical properties, making them interesting novel candidates for future applications. Furthermore, we demonstrate that in <i>S. reilianum,</i> a combination of two gene clusters is necessary for MEL biosynthesis, which enables a glimpse into the evolutionary history of the altered MEL species.