Transcription Factors From Haematococcus pluvialis Involved in the Regulation of Astaxanthin Biosynthesis Under High Light-Sodium Acetate Stress

The microalgae Haematococcus pluvialis attracts attention for its ability to accumulate astaxanthin up to its 4% dry weight under stress conditions, such as high light, salt stress, and nitrogen starvation. Previous researches indicated that the regulation of astaxanthin synthesis might happen at the transcriptional level. However, the transcription regulatory mechanism of astaxanthin synthesis is still unknown in H. pluvialis. Lacking studies on transcription factors (TFs) further hindered from discovering this mechanism. Hence, the transcriptome analysis of H. pluvialis under the high light-sodium acetate stress for 1.5 h was performed in this study, aiming to discover TFs and the regulation on astaxanthin synthesis. In total, 83,869 unigenes were obtained and annotated based on seven databases, including NR, NT, Kyoto Encyclopedia of Genes and Genomes Orthology, SwissProt, Pfam, Eukaryotic Orthologous Groups, and Gene Ontology. Moreover, 476 TFs belonging to 52 families were annotated by blasting against the PlantTFDB database. By comparing with the control group, 4,367 differentially expressed genes composing of 2,050 upregulated unigenes and 2,317 downregulated unigenes were identified. Most of them were involved in metabolic process, catalytic activity, single-organism process, single-organism cellular process, and single-organism metabolic process. Among them, 28 upregulated TFs and 41 downregulated TFs belonging to 27 TF families were found. The transcription analysis showed that TFs had different transcription modules responding to the high light and sodium acetate stress. Interestingly, six TFs belonging to MYB, MYB_related, NF-YC, Nin-like, and C3H families were found to be involved in the transcription regulation of 27 astaxanthin synthesis-related genes according to the regulatory network. Moreover, these TFs might affect astaxanthin synthesis by directly regulating CrtO, showing that CrtO was the hub gene in astaxanthin synthesis. The present study provided new insight into a global view of TFs and their correlations to astaxanthin synthesis in H. pluvialis.