Investigation of SNPs at NKCC Gene of Scylla paramamosain to Unveil the Low-Salinity Tolerance Phenotype

The Na+/K+/2Cl− cotransporter (NKCC) gene encodes a critical membrane transporter involved in cellular ion homeostasis and plays a pivotal role in osmoregulation and salinity adaptation in aquatic organisms. This study identified and validated SNP markers in the NKCC gene associated with low-salinity tolerance in Scylla paramamosain. Four SNPs (g.196C>A, g.8374T>A, g.8385T>A and g.91143T>A) were screened and genotyped in low-salinity tolerant and intolerant groups. Association analysis revealed that mutant genotypes at all four sites were significantly enriched in the tolerant group (p <0.05), with the values of odds ratios (OR) greater than 1. The tolerant group exhibited significantly higher genetic diversity than the intolerant group. Haplotype analysis showed the wild CTTT haplotype dominated in the intolerant group, while mutant-containing haplotypes were significantly elevated in the tolerant group. A positive correlation was observed between the mutant and NKCC expression. Functional validation by qRT-PCR demonstrated that mutant allele carriers exhibited significantly higher NKCC mRNA expression levels than the wild-type carriers. Moreover, the expression level of homozygous mutations is significantly higher than that of heterozygous mutations. These validated SNPs could provide effective molecular markers for marker-assisted selection breeding of low-salinity tolerant S. paramamosain strains, offering important theoretical and practical implications for sustainable aquaculture development.