Transcription Levels of SDR Gene <i>Ao274</i> in Nematode-Trapping Fungus <i>Arthrobotrys oligospora</i> Regulates Configurations and Oxidation Patterns of Arthrobotrisins and Formation of Trapping Devices

Here, we report hierarchical functions of a putative short-chain dehydrogenase/reductase gene <i>Ao274</i> for arthrobotrisin biosynthesis in nematode-trapping fungus Arthrobotrys oligospora via an enhanced promoter. Transcriptional analysis revealed that <i>Ao274</i> exhibited much higher transcriptional levels than all other genes in the arthrobotrisin biosynthetic pathway. We generated four mutants of two types with varying reductions in <i>Ao274</i> transcription through gene swap experiments. Target isolation and structural elucidation of ten novel intermediates accumulated in the mutants demonstrated that high transcriptional levels are crucial for the hierarchical activity of <i>Ao274</i>, which is responsible for double carbonyl reductions and oxygenations at distinct carbon positions, preferentially acting on carbonyl reduction at C-1, followed by oxygen addition at C-1′. Additionally, variations in <i>Ao274</i> transcription levels significantly affected conidial formation and trapping device development in A. oligospora. Our findings provide new insights into the chemical and biological functions of short-chain dehydrogenase/reductase family genes regulated by transcriptional levels.