Qi Li, Xuelin Zhao, Hong Yu

College of Fisheries, Ocean University of China, Qingdao 266003, China


Keywords: Crassostrea gigas; salinity stress; transcriptome sequencing; microRNA; WGCNA

Environmental salinity creates a key barrier to limit the distribution of most aquatic organisms. Adaptation to osmotic fluctuation is believed to be a factor facilitating species diversification. In recent years, due to global warming, the huge amount of freshwater inflow disproportionately affect the seas and oceans. Salinity of the superficial water and inshore water decreased acutely in rainy season, which can incur the increasing mortality outbreaks and distribution shifts of marine species. Crassostrea gigas, due to its sessile lifestyle, worldwide distribution and intertidal habitat, it provide an excellent model system to study the osmoregulation mechanism of osmoconformers and the effects of the salinity.

In this study, comparative transcriptome anaylsis and miRNA transcritpome analysis between C. gigas and C. hongkongensis were used to identify the differentially expressed transcripts and miRNAs in response to acute osmotic stress. There are 48 and 408 differentially expressed gene identified in C. gigas and C. hongkongensis. A total of 202 and 87 miRNAs were identified from C. gigas and C. hongkongensis, respectively. Six miRNAs in C. gigas and two in C. hongkongensis were differentially expressed in response to osmotic stress. The expression profiles of these eight miRNAs were validated by qRT-PCR. Based on the data of transcriptome, we analyzed the processes of oyster to respond to low salinity and explained the molecular mechanism comparing to the studies in other species. Then we re-analyzed the RNA-seq data of C. gigas under seven different salinity gradients for seven days using weighted gene correlation network analysis (WGCNA). According to the expression of genes, all the genes were separated to different modules. Correlating the module and phenotypic characters, we constructed the gene co-expression network to reveal the pathways related to salinity tolerance in oyster. Finally, we cloned the gene encoding a key enzyme involved in the pathway of taurine metabolism. The expression pattern of cysteine sulfinate decarboxylase (CSAD) under low salinity stress were conducted using qPCR and RNA interference. The results in this study may provide a better understanding of the mechanism of osmoregulation in marine mollusca.