Gamma-aminobutyric acid coupled with copper ion stress stimulates lipid production of green microalga Monoraphidium sp. QLY-1 through multiple mechanisms.

• Lipid content was improved by GABA coupled with Cu2+ stress. • GABA regulated reactive oxidative species (ROS) signalling under Cu2+ stress. • GABA coupled with Cu2+ stress upregulated the levels of lipid-related genes and atg8. • Autophagy activation influenced lipid synthesis in alga under GABA and Cu2+ stress. Induction of copper ion (Cu2+) stress is a method used to increase lipid accumulation in microalgae, but it decreases cell growth. In this work, the impacts of gamma-aminobutyric acid (GABA) coupled with Cu2+ stress on the biomass and oil yield in Monoraphidium sp. QLY-1 were investigated. Results suggested that the combined treatment of GABA and Cu2+ resulted in a higher lipid content (55.13%) than Cu2+ treatment (48.43%). Furthermore, GABA addition upregulated the levels of lipid-relevant genes, cellular GABA, ethylene (ETH), and antioxidant enzyme activities and alleviated oxidative damage caused by Cu2+ stress. The autophagy-relevant gene atg8 was also upregulated by GABA treatment. Further exploration indicated that cell autophagy induced the lipid content up to 58.09% with GABA and Cu2+ stress treatment. This investigation demonstrates that the coupling strategy can stimulate lipid production and shed light on the underlying mechanisms in lipid biosynthesis, cell autophagy, and stress response of microalgae. [ABSTRACT FROM AUTHOR]