Abstract
Haematococcus pluvialis accumulates a large amount of astaxanthin under various stresses, e.g., blue light and salicylic acid (SA). However, the metabolic response of H. pluvialis to blue light and SA is still unclear. We investigate the effects of blue light and SA on the metabolic response in H. pluvialis using both transcriptomic and proteomic sequencing analyses. The largest numbers of differentially expressed proteins (DEPs; 324) and differentially expressed genes (DEGs; 13,555) were identified on day 2 and day 7 of the treatment with blue light irradiation (150 μmol photons m−2s−1), respectively. With the addition of SA (2.5 mg/L), a total of 63 DEPs and 11,638 DEGs were revealed on day 2 and day 7, respectively. We further analyzed the molecular response in five metabolic pathways related to astaxanthin synthesis, including the astaxanthin synthesis pathway, the fatty acid synthesis pathway, the heme synthesis pathway, the reactive oxygen species (ROS) clearance pathway, and the cell wall biosynthesis pathway. Results show that blue light causes a significant down-regulation of the expression of key genes involved in astaxanthin synthesis and significantly increases the expression of heme oxygenase, which shows decreased expression by the treatment with SA. Our study provides novel insights into the production of astaxanthin by H. pluvialis treated with blue light and SA.
Highlights
Astaxanthin (3,30 -dihydroxy-β-carotene-4,40 -dione) is a type of red-orange carotenoid with strong biological antioxidant capacity [1] and important applications in human health and in the nutraceutical, cosmetics, food, and feed industries [2]
Our study clearly demonstrated that the combined analysis of RNA-seq and proteomic sequencing comprehensively revealed the variations in the molecular mechanisms of H. pluvialis in response to different wavelengths of light and salicylic acid (SA), further providing essential insights into the metabolic regulation involved in the synthesis of astaxanthin at molecular level
H. pluvialis was exposed to high-intensity blue light and SA, resulting in alterations in gene and protein expressions from those derived from exposure to white light of high intensity
Summary
Astaxanthin (3,30 -dihydroxy-β-carotene-4,40 -dione) is a type of red-orange carotenoid with strong biological antioxidant capacity [1] and important applications in human health and in the nutraceutical, cosmetics, food, and feed industries [2]. During the process of astaxanthin synthesis, isopentenyl diphosphate (IPP) reacts with dimethylallyl diphosphate (DMAPP) to form geranyl pyrophosphate (GPP), which joins another molecule of IPP to form farnesyl pyrophosphate (FPP). FPP joins IPP to create geranylgeranyl pyrophosphate (GGPP). Two molecules of GGPP are connected to generate phytoene, which undergoes multiple dehydrogenation reactions to produce lycopene. Lycopene undergoes two reactions to produce β-carotene and to generate astaxanthin [3]. Compared with other species of microalgae, Haematococcus pluvialis has shown the highest accumulation of astaxanthin—up to 4% of dry cell weight (DCW) [4]. In the production of astaxanthin, H. pluvialis goes through two developmental stages, including the dividing stage (morphologically green, producing macrozooids or zoospores and microzooids) and the astaxanthin accumulating stage (morphologically red, producing palmella and hematocysts or aplanospores). In the astaxanthin accumulating stage, the green dividing cells of
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