Transcriptional responses of Aurantiochytrium limacinum under light conditions

Astaxanthin-producing protist Aurantiochytrium limacinum can accumulate higher amounts of astaxanthin under light conditions; however, little is known about the impact of light exposure on its metabolism. Here, we investigated the transcriptional profile of A. limacinum under light conditions.Transcriptomic analyses revealed that 962 genes of A. limacinum showed a significant change in expression under light conditions, most of which (94.5%) were downregulated. Furthermore, gene ontology enrichment analysis indicated that A. limacinum mainly downregulated genes associated with cell motility, proliferation and gene expression processes, whose activities depend on ATP as an energy source. Additionally, the quantification of carotenoid and its transcripts suggested that β-carotene and astaxanthin biosynthesis pathways were rate-limiting and tightly regulated steps, respectively. In comparison, these processes were enhanced under light conditions.Considering that astaxanthin accumulation was highly correlated with reactive oxygen species (ROS) levels in microalgae, our results suggest that A. limacinum reduces ATP consumption to decrease the occurrence of ROS in mitochondria while accumulating astaxanthin to prevent ROS damage.This study provides novel insights into the impact of light exposure on A. limacinum metabolism, thereby facilitating a complete understanding of this protist for efficient astaxanthin production.