Functional characterization of four ToRac genes and their association with anti-parasite traits in Trachinotus ovatus (Linnaeus, 1758)

Abstract

Rac (Ras-related C3 botulinum toxin substrate), belonging to the Rho GTPase family, has various critical cellular functions. However, research on this topic in fish has rarely been reported. In the present study, to comprehend the expression patterns of the Rac1a, Rac1b, Rac2, and Rac3 genes and their association with antiparasitic traits in Trachinotus ovatus, the sequences of four ToRac genes were obtained from the genome database and verified. Their expression profiles were detected by qRT–PCR, and direct sequencing was implemented to screen and genotype SNPs. All four ToRac genes contained a 579 bp ORF encoding a putative amino acid sequence with 192 residues. Furthermore, the conserved RHO domain was found in the amino acid sequences of four ToRacs. The Rac1a, Rac1b, Rac2, and Rac3 genes were widely expressed in various tissues of healthy T. ovatus. All four ToRac genes were upregulated in both the skin and gill, which were local infection sites after Cryptocaryon irritans challenge. Eleven SNPs were identified in the four ToRac genes; six SNP loci were located in exons, and five SNP loci were located in promoters. Moreover, the allele and genotype frequencies of SNP-ToRac1 + 6864 T/G were dramatically different between the susceptible and resistant groups (P < 0.05). In those two groups, the allele frequency of SNP-ToRac3 + 4116 G/T was observably different (P < 0.05); however, the genotype frequency of this SNP was not significantly different. These findings suggest that Racs play an important role in the immune response to C. irritans in T. ovatus.