Salinity Acclimation Induces Reduced Energy Metabolism, Osmotic Pressure Regulation and Transcriptional Reprogramming in Hypotrichida Ciliate Gastrostyla setifera.

Coastal and estuarine protists are frequently exposed to salinity undulation. While the tolerance and stress responses of microalgae to salinity have been extensively studied, there have been scarce studies on the physiological response of heterotrophic protists to salinity stressing. In this study, we investigated the physiological response of the heterotrophic ciliate Gastrostyla setifera to a salinity of 3, via a transcriptomic approach. The first transcriptome of genus Gastrostyla was obtained utilizing a group of manually isolated ciliate individuals (cells) and RNA-seq technique. The completeness of the transcriptome was verified. Differentially expressed gene (DEG) analysis was performed among the transcriptomes of G setifera acclimated in saline water (salinity 3) and those cultured in fresh water. The results demonstrated a significant alternation in gene transcription, in which the ciliate exhibits a transcripttomic acclimation in responding salinity stressing. The up-regulated DEGs were enriched in the pathways of cytoskeleton proteins, membrane trafficking, protein kinases and protein phosphatases. These may represent enhanced functions of ion transport, stress response and cell protections. Pathways involved in energy metabolism and biosynthesis were markedly down-regulated, reflecting decreased cell activity. Particularly, we detected significantly down-regulated genes involved in several pathways of amino acid catabolism, which may lead to accumulation of amino acids in the ciliate cell. Amino acid could act as compatible solutes in the cytoplasm to maintain the osmotic balance in saline water. Overall, this work is an initial exploration to the molecular basis of the heterotrophic protist responding to salinity stressing. The result sheds light on the mechanisms of enhancement of cell protection, reduction of cell activity, and osmotic pressure regulation in ciliates acclimated to salinity. [ABSTRACT FROM AUTHOR]