However, when the oxidation-reduction process homeostasis is disturbed, oxidative stress may lead to aberrant cell death and contribute to disease development. This reseach suggested that exposure to salinity stress, especially the high salinity stress has been shown to active the oxidation-reduction process in Portunus trituberculatus in order to balance the level of ROS/RNS. Of course, there was another possibility that the oxidation-reduction process in Portunus trituberculatus has been disturbed in this high salinity stress. Both cellular protein modification and phosphorylation process belong to the scope of post-translational modifications. Posttranslational modifications modulate the activity of most eukaryote proteins which. manifest as chemical modifications that occur on amino acid side chains in a sitespecific manner. They can temporarily or permanently change the fate of the protein by enhancing the functionality and/or stability of the target protein through the recruitment of auxiliary factors, change the proteins’ cellular localisation or signal the most terminal fate, proteasomal degradation. Our data showed that many gene were enrichmented in cellular protein modification and phosphorylation process, suggested that posttranslational modifications play an important role in osmoregulation of Portunus trituberculatus, and further research is worthwhile. Many differentially expressed unigenes enriched in chitin metabolic process with the maximum enrichment level were aslo found in our data, which suggested chitin metabolic process may be involved in osmoregulation or affected by salinity stress. Further analysis found there were 4 chitinase genes. In crustaceans, during the molting cycle, chitinase dissolves chitin in the old exoskeleton into more soluble forms, which can then be partially reabsorbed into the body and used to synthesize the new exoskeleton. Therefore, the chitinase are indispensable for crustaceans. By now, many genes encoding Epimedoside-A chitinases have been isolated and characterized in crustaceans due to their importance in growth, development and immunity. However, chitinase with function of osmoregulation has not been reported in crustacea. More detailed research can be done according to the connections between the salinity changes and chitin metabolic process in the future. Small GTP-binding genes play a crucial regulatory role in a number of cellular processes in both plants and ani-mals, such as vesicle-mediated intracellular traf?cking, signal transduction, cytoskeletal organization, and cell division. Differential expression of small GTP-binding proteins has been previously reported in various abiotic stresses in plant, animal, and Lomitapide Mesylate bacteria, however, the functions of Small GTP-binding genes was little known in crustacea. 15 unigenes were enriched in GTPase mediated signal transduction process with a relatively low p-value implied that GTPase mediated signal transduction process plays an important role in Portunus trituberculatus salinity adaptation. In addition, 17 up-regulated unigenes were enriched in carbohydrate metabolic process in high salinity stress suggested that hypo-osmoregulation of Portunus trituberculatus depends on energy consumption. This result have also been reported in Xu’s studies and further experiments are needed to verify the hypothesis. It should be noted that, the processes of response to oxidative stress, defense response, response to oxidative stress and defense response to bacterium were enriched in salinity stess, and lots of stress-related and immunity-related genes such as HSP, cathepsin, lectin, serine protease, and peroxiredoxin show significantly up-regulated or downregulation expression responding to low or high salinity stress.