Transcriptome analysis reveals the promoting effect of trisodium citrate on astaxanthin accumulation in Haematococcus pluvialis under high light condition

Abstract Some organic carbons were able to further promote astaxanthin accumulation in Haematococcus pluvialis under stress conditions. In this study, we demonstrate that adding 0.6 mM trisodium citrate (TSC) into the culture media increased astaxanthin content in the single cell by 2.4 folds and increased astaxanthin yield by 11.9% in H. pluvialis at day 7 under high light stress. In addition, the ROS level, which was highly associated with astaxanthin accumulation, was also increased by TSC. Subsequent comparative transcriptomic analysis revealed the mechanism underlying the promoting effect of trisodium citrate on astaxanthin accumulation. TSC treatment up-regulated significantly the expression of many enzyme encoding genes involved in TCA cycle, glucose metabolism, astaxanthin biosynthesis and fatty acids metabolism. In addition, trisodium citrate treatment significantly changed the expression of genes involved in ROS scavenging and cell wall biosynthesis. Our results indicated that TSC can not only be used as a carbon source but also further increase the ROS level in H. pluvialis under high light stress. Collectively, this study provides a new method that can increase astaxanthin yield, but also insights into the mechanism of trisodium citrate-induced astaxanthin biosynthesis in H. pluvialis under high light.