The nitrogen regulator AreA modulates lipid metabolism through uga2 in Mucor circinelloides

Oleaginous filamentous fungus Mucor circinelloides harbors a GATA transcription activator AreA, which regulates nitrogen metabolism. In our previous study, deletion of AreA resulted in increased lipid production, while its overexpression reduced lipid synthesis. Although it is not a direct lipogenesis regulator, AreA influences metabolic flux by modulating nitrogen utilization pathways, which in turn affects carbon distribution. One such pathway is the GABA shunt, an alternative route that bypasses two steps of TCA cycle and contributes to replenishing TCA intermediates under nitrogen-limited conditions. The uga2 gene, encoding succinate semialdehyde dehydrogenase, plays a key role in this shunt. We constructed UGA2-knockout strain in wild-type, AreA-knockout and AreA-overexpression strains, respectively. Results showed that single knockout of uga2 increased fatty acid content from 24.5 % to 32.7 %, while double knockout of areA and uga2 exhibited the highest fatty acid content at 36.1 %. The areA overexpression combined with uga2 knockout also resulted in increased lipid accumulation up to 32.4 %. The gene expression levels and enzyme activities related to fatty acid synthesis showed that deletion of uga2 may lead to carbon-nitrogen metabolism disequilibrium, shifting carbon flux towards lipogenesis. This indicated that AreA might regulate lipid metabolism through the modulation of uga2 in M. circinelloides.