Transcriptome-based analysis of the effects of salicylic acid and high light on lipid and astaxanthin accumulation in Haematococcus pluvialis

Abstract

Background: The unicellular alga Haematococcus pluvialis has achieved considerable interests for its capacity to accumulate large amounts of triacylglycerol and astaxanthin under various environmental stresses. To our knowledge, studies focusing on transcriptome research of H. pluvialis under exogenous hormones together with physical stresses are rare. In the present study, the change patterns at transcriptome level were analyzed to distinguish the multiple defensive systems of astaxanthin and fatty acid metabolism against exogenous salicylic acid and high light (SAHL) stresses. Results: Based on RNA-seq data, a total of 112,463 unigenes and 61,191 genes were annotated in six databases, including NR, KEGG, Swiss-Prot, PFAM, COG and GO. Analysis of differentially expressed genes (DEGs) in KEGG identified many transcripts that associated with the biosynthesis of primary and secondary metabolites, photosynthesis, and immune system responses. Furthermore, 705 unigenes predicted as putative transcription factors (TFs) were identified, and the most abundant TFs families were likely to be associated with the biosynthesis of astaxanthin and fatty acid in H. pluvialis upon exposure to SAHL stresses. Additionally, majority of the fifteen key genes involved in astaxanthin and fatty acid biosynthesis pathways presented the same expression pattern, resulting in increased accumulation of astaxanthin and fatty acids in single celled H. pluvialis, in which astaxanthin content increased from 0.56±0.05 mg·L-1 at stage Control to 0.89±0.12 mg·L-1 at stage SAHL_48. And positive correlations were observed among these studied genes by Pearson Correlation (PC) analysis, indicating the coordination between astaxanthin and fatty acid biosynthesis. In addition, protein–protein interaction (PPI) network analysis also demonstrated that this coordination might be at transcriptional level.Conclusion: The results in this study provided valuable information to illustrate the molecular mechanisms of coordinate relations between astaxanthin and fatty acid biosynthesis. And salicylic acid might play a role in self-protection processes of cells, helping adaption of H. pluvialis to high light stress.

Transcriptome Analysis of the Accumulation of Astaxanthin in Haematococcus pluvialis Treated with White and Blue Lights as well as Salicylic Acid

“…Furthermore, our results showed that the genes related to photosynthesis were significantly downregulated in the later stage of the treatment of high-intensity white light irradiation, blocking the synthesis of photosynthetic pigment (i.e., chlorophyll), while the genes involved in the synthesis of carotenoids and fatty acids were significantly upregulated in the later stage of light stress. These results were consistent with those reported previously [23].…”

“…The results showed that under the stress of blue light, white light, and blue light with SA for 2 d and 7 d, the contents of astaxanthin in H. pluvialis were significantly increased compared with that of the control group with the combined treatment of both blue light and SA achieving the highest content of astaxanthin, while the blue light generated the lowest production of astaxanthin (Figure 1). These results were consistent with those reported previously, showing the effect of SA as a plant growth regulator on promoting the accumulation of astaxanthin in H. pluvialis by providing additional carbon sources for the synthesis of astaxanthin [23]. Furthermore, studies showed that either blue light or white light promoted the accumulation of astaxanthin [24].…”

“…To investigate the effects of blue light on the accumulation of astaxanthin over time, the intersections of the comparison groups of B07 vs. N and B02 vs. N were enriched in the metabolic pathways of the KEGG database (Figure S2), with most genes enriched in the pyruvate metabolic pathway. These results were consistent with those previously reported, showing that the pyruvate metabolic pathway was enriched in H. pluvialis under stresses with similar gene expression patterns with subsequently largely the same gene expression patterns, suggesting that the pyruvate metabolism was closely related to the synthesis of astaxanthin, while the acetyl-CoA produced in the pyruvate metabolism was also essential for the lipid synthesis [23].…”

Optimization of microbial cell factories for astaxanthin production: Biosynthesis and regulations, engineering strategies and fermentation optimization strategies

“…In consistent with these findings, nitrogen limitation in the presence of high light can induce high level of astaxanthin accumulation in H. pluvialis , which was accompanied with downregulation of the TFs from bHLH family [ 68 ]. On the other hand, C3H, MYB, Nin-like, MTB_related and ERF TFs were highly expressed TF families under the effects of salicylic acid in the presence of high light [ 68 , 69 ]. In addition to TFs, some miRNAs also have been identified as responding miRNAs to sodium acetate and high light stress [ 70 ].…”

The Enhancement of Astaxanthin Production Using Medium Cultures Components, Stressors, Nanoparticles, Elicitors, and Gene Engineering in Haematococcus pluvialis

“…A group of academics found that increasing both light and salicylic acid together increased the production of astaxanthin and fat, and that there was a link between the gene network of them. (Hu et al, 2021). Some scholars showed that addition of 100 μM gibrelin acid to the medium culture of the marine Chrysophyte Monodopsis subterranean increased biomass and total fatty acid up to 3.3 and 3.9 folds respectively, also the addition of 1 μM methyl jasmonate to it increased it's biomass up to 2.7 folds.…”