Effects of salinity acclimation and eyestalk ablation on Na+, K+, 2Cl- cotransporter gene expression in the gill of Portunus trituberculatus:a molecular correlate for salt-tolerant trait

The Na+, K+, 2Cl(-) cotransporter (NKCC) is an important gene in ion transport. In order to elucidate its function, and regulatory mechanisms, in salinity acclimation, the complete cDNA sequence of NKCC (4218 bp) from Portunus trituberculatus (PtNKCC) was first cloned and characterized. It was found to encode 1055 amino acids containing conserved AA-permease and SLC12 motifs. Results show that PtNKCC is expressed to the greatest extent in gills. High salinity stress exposure led to significant increases (9.6-fold) of PtNKCC mRNA expression in the gills 12 h after treatment, declining to less than the levels seen in the control group between 48 and 72 h. During low salinity stress, expression levels of PtNKCC in gills were found to be upregulated at each sampling time, reaching their peak after 6 h (a 12.4-fold increase). Eyestalk ablation also triggered an 11.3-fold increase in PtNKCC mRNA, while re-injection with eyestalk homogenates significantly reduced the expression of PtNKCC mRNA. Four single nucleotide polymorphisms (SNPs) were detected in the PtNKCC open reading frame, and one SNP was associated with salt tolerance. Our results indicate that PtNKCC plays an important role in the salinity acclimation of P. trituberculatus, while there may be a compound present in the XOSG that inhibits the expression of PtNKCC.