Intergenic Variants Upstream of GADD45b Affect Survival of Micropterus salmoides Following LMBV Exposure

GADD45 (growth arrest and DNA damage inducible 45) is a crucial signaling regulator in cells and plays an important role in various biological processes, including cellular stress response, cell cycle control, DNA damage repair, apoptosis, and tumor suppression. Our previous studies identified GADD45b as a candidate gene associated with resistance to largemouth bass ranavirus (LMBV) infection in largemouth bass (<i>Micropterus salmoides</i>). In the present study, the upstream intergenic polymorphisms of GADD45b were investigated to explore their association with resistance/susceptibility to LMBV. We employed the kompetitive allele specific PCR (KASP) assay to genotype 118 resistant individuals and 122 susceptible individuals following LMBV infection. The results revealed that SNP38943374 C>A and SNP38943495 G>A were significantly associated with LMBV resistance/susceptibility (<i>p</i> < 0.01). Individuals with the CC genotype of SNP38943374 and the GG genotype of SNP38943495 were more prevalent in resistant groups and have advantages in survival time after LMBV infection. Linkage disequilibrium analysis indicated strong linkage among these two loci. The distinct dynamic expression patterns of GADD45b in different genotypes following LMBV infection suggest its functional role in viral infection. Additionally, dynamic expression levels of immune-related genes (IFN-γ, TNF-α, and IL-10) also varied among different genotypes. These results demonstrated that the two SNPs in GADD45b could be used as candidate markers for further investigation of selective breeding of resistant largemouth bass to LMBV.