Astaxanthin accumulation difference between non-motile cells and akinetes of Haematococcus pluvialis was affected by pyruvate metabolism

Abstract

Background: Haematococcus pluvialis is the best source of natural astaxanthin, known as the king of antioxidants. H. pluvialis have four cell forms: spore, motile cell, non-motile cell and akinete. Spores and motile cells are susceptible to photoinhibition and would die under photoinduction conditions. Photoinduction using non-motile cells as seeds could result in a higher astaxanthin production than that using akinetes. However, the mechanism of this phenomenon has not been clarified. Results:Transcriptome was sequenced and annotated to illustrate the mechanism of this phenomenon. All differentially expressed genes involved in astaxanthin biosynthesis were up-regulated. Particularly, chyb gene was up-regulated by 16-fold, improving the conversion of β-carotene into astaxanthin. Pyruvate was the precursor of carotenoids biosynthesis. Pyruvate kinase gene expression level was increased by 2.0-fold at the early stage of akinetes formation. More changes of gene transcription occurred at the early stage of akinetes formation, 52.7% and 51.9% of total DEGs in control group and treatment group, respectively. Conclusions:Genes transcription network was constructed and the synthesis mechanism of astaxanthin was clarified. The results are expected to further guide the in-depth optimization of the astaxanthin production process in H. pluvialis by improving pyruvate metabolism.

Unveiling the underlying molecular basis of astaxanthin accumulation in Haematococcus through integrative metabolomic-transcriptomic analysis

“…2. These results are in agreement with previous transcriptomic data (Fang et al, 2020;Gao et al, 2015;He et al, 2018) obtained under different stress conditions. Following the β-branch, higher expression of β β-carotene ketolase (BKT) and β β-carotene hydroxylase (CHYB) was detected in correspondence with 9 and 15-fold higher canthaxanthin and astaxanthin content, respectively, in reddish cells.…”

“…Following the β-branch, higher expression of β β-carotene ketolase (BKT) and β β-carotene hydroxylase (CHYB) was detected in correspondence with 9 and 15-fold higher canthaxanthin and astaxanthin content, respectively, in reddish cells. The oxygenations catalysed by these enzymes are regarded as rate limiting steps of astaxanthin synthesis in Haematococcus (Fang et al, 2020). Again, this agrees with results reported for Haematococcus subjected…”

“…In reddish Haematococcus cells, no significant higher expression than in green cells of the gene codifying for malate dehydrogenase (MDH) was observed, but one of the two isoforms codifying for phosphoenolpyruvate carboxykinase (PEPCK) was indeed highly upregulated (30-fold), a situation leading to enhanced synthesis of PEP from oxaloacetate (OAA) that would result in additional availability of pyruvate for both, FA and astaxanthin production. Fang et al (2020) have described the upregulation of MDH2 and PEPC enzymes in heterotrophically grown non-motile cells.…”

“…Haematocysts are bigger in size than other morphotypes and are characterized by a thick cell wall and a massive accumulation of astaxanthin that is assumed to be linked to cessation of growth (Fábregas et al, 2001). Nevertheless, astaxanthin accumulation has also been described to take place in vegetative morphotypes (Del Río et al, 2005;Fang et al, 2020). In this context, Fang et al (2020) have proposed the non-motile cell as a most appropriate cell type for astaxanthin photoinduction.…”

“…Nevertheless, astaxanthin accumulation has also been described to take place in vegetative morphotypes (Del Río et al, 2005;Fang et al, 2020). In this context, Fang et al (2020) have proposed the non-motile cell as a most appropriate cell type for astaxanthin photoinduction.…”