ROS Induce β-Carotene Biosynthesis Caused by Changes of Photosynthesis Efficiency and Energy Metabolism in Dunaliella salina Under Stress Conditions.

Yimei Xi,Zhanyou Chi,Fantao Kong

doi:10.3389/fbioe.2020.613768

Abstract

The unicellular alga Dunaliella salina is regarded as a promising cell factory for the commercial production of β-carotene due to its high yield of carotenoids. However, the underlying mechanism of β-carotene accumulation is still unclear. In this study, the regulatory mechanism of β-carotene accumulation in D. salina under stress conditions was investigated. Our results indicated that there is a significant positive correlation between the cellular ROS level and β-carotene content, and the maximum quantum efficiency (Fv/Fm) of PSII is negatively correlated with β-carotene content under stress conditions. The increase of ROS was found to be coupled with the inhibition of Fv/Fm of PSII in D. salina under stress conditions. Furthermore, transcriptomic analysis of the cells cultivated with H2O2 supplementation showed that the major differentially expressed genes involved in β-carotene metabolism were upregulated, whereas the genes involved in photosynthesis were downregulated. These results indicated that ROS induce β-carotene accumulation in D. salina through fine-tuning genes which were involved in photosynthesis and β-carotene biosynthesis. Our study provided a better understanding of the regulatory mechanism involved in β-carotene accumulation in D. salina, which might be useful for overaccumulation of carotenoids and other valuable compounds in other microalgae.

Highlights

Carotenoids are light-harvesting pigments that act as antioxidant molecules
To study whether various stress conditions result in the same oxidative stress for carotenoid accumulation, we compared the effect of different stress conditions on βcarotene and biomass production in D. salina
The cell growth was arrested under N– and high salinity (HS) conditions, β-carotene accumulation was enhanced under all the stress conditions tested

Summary

Introduction

Carotenoids are light-harvesting pigments that act as antioxidant molecules. Β-carotene is a high-value carotenoid that can be produced in many marine animals, higher plants, and microorganisms including microalgae. Due to its strong pigmentation function, powerful antioxidative activity, and broad beneficial effects on human health, β-carotene possesses a wide range of applications in feed, food, and nutraceutical and pharmaceutical industries, which has attracted great attention (Jin and Melis, 2003; Combe et al, 2015; Liang et al, 2019). Humans cannot synthesize β-carotene and must obtain it through diet. In 2015, the global βcarotene market was approximately estimated to be US$ 432 million with 36% revenues from microalga-derived natural β-carotene (Nethravathy et al, 2019)

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Conclusion