Gamma-aminobutyric acid as a regulator of astaxanthin production in Haematococcus lacustris under salinity: Exploring physiology, signaling, autophagy, and multi-omics landscape

Haematococcus lacustris-derived natural astaxanthin has significant commercial value, but stressful conditions alone impair cell growth and reduce the total productivity of astaxanthin in industrial settings. This study used gamma-aminobutyric acid (GABA) to increase biomass, astaxanthin productivity, and tolerance to salinity. GABA under NaCl stress enhanced the biomass to 1.76 g/L, astaxanthin content to 30.37 mg g⁻¹, and productivity to 4.10 mg/L d⁻¹, outperforming the control. Further analysis showed GABA enhanced nitrogen assimilation, Ca²⁺ level, and cellular GABA content, boosting substrate synthesis, energy metabolism, osmoregulation, autophagy, and antioxidant defenses. GABA also activated signaling pathways involving phytohormones, cAMP, cGMP, and MAPK, aiding astaxanthin synthesis. The application of biomarkers (ethylene, salicylic acid, trans-zeatin) and an autophagy inhibitor cooperated with GABA to further enhance the total astaxanthin productivity under NaCl stress. Combining GABA with 25 μM salicylic acid maximized astaxanthin yield at 4.79 mg/L d⁻¹, offering new strategies for industrial astaxanthin production.