Homologous Overexpression of Phosphatidate Phosphatase ( <i>Lipin</i> ) in the Oleaginous Fungus <i>Mucor circinelloides</i> WJ11 Enhances Lipid Accumulation under Static Solid Cultivation and Submerged Fermentation

<i>Lipin</i>, a phosphatidic acid phosphatase, catalyzes the conversion of phosphatidic acid to diacylglycerol, a key step in triacylglycerol (TAG) biosynthesis, and acts as a transcriptional coregulator of lipid metabolism. In this study, the <i>Lipin</i>-encoding gene (McLipin) was overexpressed in <i>Mucor circinelloides</i> WJ11 to evaluate its impact on lipid accumulation under submerged (SmF) and solid-state fermentation (SSF). Under SSF, McLipin overexpression increased cell dry weight by 19% in spores and 36.9% in mycelia compared to the control strain. Total fatty acid (TFA) content increased by 35.7% in mycelia, while in spores it increased from 10% to 18% of dry cell weight, indicating a substantial enhancement in lipid yield. Fatty acid profiling showed elevated proportions of C16:0, C18:2, and C18:3 and a reduced C18:1 content. RT-qPCR indicated that McLipin expression peaked at 24 h under SSF, coinciding with upregulation of <i>ACC</i>, <i>FAS</i>, <i>cME</i>, and NADPH-generating genes. These results suggest that McLipin overexpression reprograms lipid metabolism, significantly enhancing TAG biosynthesis under SSF for potential industrial lipid production.