Enhancing astaxanthin and lipid coproduction in Haematococcus pluvialis by the combined induction of plant growth regulators and multiple stresses.

• Integration of MT and Put further promotes astaxanthin and lipids production. • MT and Put treatment upregulate carotenogenesis and lipogenesis. • MT and Put alleviate oxidative stress-caused by abiotic stresses in H. pluvialis. • MT and Put regulate GABA and ROS signallings. Coupling chemical induction and abiotic stresses is a beneficial strategy for astaxanthin (Asta) induction in Haematococcus pluvialis. The combined application of melatonin (MT) and putrescine (Put) induced Asta and lipid biosynthesis in H. pluvialis under adverse conditions. Under MT and Put inductions, the highest Asta and lipid contents were 3.64% and 55.84%, which were 1.71- and 1.17-times higher than the control group, respectively. The combination of MT and Put also enhanced the expression of carotenogenic, lipogenic and antioxidant enzyme genes. Additionally, this combined treatment increased the endogenous Put content while decreasing the reactive oxygen species (ROS) and γ-aminobutyric acid (GABA) levels. Further results proved that endogenous Put promoted Asta production and alleviated oxidative stress by regulating carotenogenesis and GABA and ROS signaling. This study describes a potential process for stimulating Asta and lipid coproduction and highlights the connections among MT, Put, signaling molecules, Asta and lipid synthesis in H. pluvialis. [ABSTRACT FROM AUTHOR]