Efficient microalgal lipid production driven by salt stress and phytohormones synergistically

[Display omitted] •Phytohormones increased the growth rate of microalgae under salt stress.•Phytohormones further increased the microalgal lipid content based on salt stress.•2 g/L salt and ABA increased lipid productivity to 3.7 times that of control.•DEGs of microalgae were mainly up-regulated under phytohormones except BL.•The regulation of different phytohormones is related to homologous recombination. In this study, a novel method of coupling phytohormones with saline wastewater was proposed to drive efficient microalgal lipid production. All the six phytohormones effectively promoted microalgae growth in saline wastewater, and further increased the microalgal lipid content based on salt stress, so as to achieve a large increase in microalgal lipid productivity. Among the phytohormones used, abscisic acid had the most significant promoting effect. Under the synergistic effect of 20 g/L salt and 20 mg/L abscisic acid, the microalgal lipid productivity reached 3.7 times that of the control. Transcriptome analysis showed that differentially expressed genes (DEGs) of microalgae in saline wastewater were mainly up-regulated under the effects of phytohormones except brassinolide. Common DEGs analysis showed that phytohormones all regulated the expression of genes related to DNA repair and substance synthesis. In conclusion, synergistic effect of salt stress and phytohormones can greatly improve the microalgal lipid production efficiency.