Identification of microRNAs involved in astaxanthin accumulation responding to high light and high sodium acetate (NaAC) stresses in Haematococcus pluvialis

The growth and astaxanthin production of unicellular Haematococcus pluvialis is affected by both the high light and sodium acetate (NaAC) stresses. There are sparse on studies of the regulatory pathways of microRNAs (miRNAs) and their target genes in response to high light and NaAC stresses in H. pluvialis. In this study, transcriptomic analysis was used to identify the key target genes of miRNA regulation under both high light and NaAC stresses. A total of 434 (including 29 novel) miRNAs were identified, which were mainly enriched in metal ion binding and transport, and involved in basic metabolic pathways, such as pyruvate metabolism, ubiquitin mediated proteolysis, and oxidative phosphorylation. A total of 115 (out of 434) miRNAs were detected in response to high light and NaAC stresses. A total of 83 and 46 miRNAs significantly expressed under high light and NaAC stresses were considered as high light and NaAC stress responsive miRNAs, respectively. 14 miRNAs responded to both high light and NaAC stresses. Some miRNAs that regulate differentially expressed target genes had been identified. In the high light treatment group, 38 regulatory pairs were identified. In NaAc treatment group, 40 regulatory pairs were identified. These results shed light on the regulatory mechanisms of miRNAs responding to high light and NaAC stresses in H. pluvialis, further providing support for understanding the molecular mechanisms of miRNA regulation involved in astaxanthin synthesis in H. pluvialis.