Reactive oxygen species derived from NADPH oxidase regulate astaxanthin and total fatty acid accumulation in Chromochloris zofingiensis

Abstract

Many abiotic stresses can promote astaxanthin and total fatty acid (TFA) accumulation in microalgae, but their signal molecules remain undetermined. The reactive oxygen species (ROS) derived from NADPH oxidase has been reported to act as signals and regulate many cellular responses in cell responses to biotic and abiotic stresses in higher plants. The present study explored the regulatory effects of NADPH oxidase derived ROS on astaxanthin and TFA accumulation in the green alga Chromochloris zofingiensis under nitrogen starvation. Diphenylene iodonium (DPI) inhibition of NADPH oxidase significantly decreased the cellular ROS level under nitrogen starvation. This was accompanied with the decreasing of astaxanthin and secondary carotenoids content, and the increasing of primary carotenoids content. Molecular studies showed that DPI depressed the expression of PSY, LCYb, and BKT, but elevated that of LCYe, which were coordinated with carotenoids content. Meanwhile, the TFA and neutral lipid contents, and the expression of their key biosynthesis genes, ACCase and PDAT, were also reduced in the DPI-treated cells. Additionally, the addition of ROS scavenger, N-acetylcysteine (NAC), decreased the astaxanthin and TFA contents. Taken together, our results revealed that NADPH oxidase-derived ROS was the key regulator in astaxanthin and fatty acid accumulation under nitrogen starvation.