Role of Ras‐related C3 botulinum toxin substrate (Rac2) in northern snakehead ( Channa argus ) resistance to Aeromonas veronii infection

Ras-related C3 botulinum toxin substrate protein (Rac2) is an important member of the Ras family. Rac has a variety of biological functions and is closely connected with cytoskeleton formation, cell signal transduction, cell adhesion and cell apoptosis. In this study, to investigate the function of northern snakehead (Channa argus) Rac2, the full-length cDNA sequence of the Rac2 gene was obtained by RACE based on a differentially expressed Rac2 gene fragment from a SSH cDNA library of northern snakehead head kidney established in a previous study, and its physicochemical properties, protein structure and amino acid homology were analysed by bioinformatics methods. Real-time fluorescence quantitative PCR was used to analyse the expression and distribution of the Rac2 gene in different tissues of northern snakehead and the changes in its expression after infection with Aeromonas veronii. The results showed that the full-length cDNA sequence of the Rac2 gene was 1179 bp, and its ORF (579 bp) encoded 192 amino acids. Amino acid alignments showed that the Rac2 sequences of different species were highly homologous. Real-time fluorescence quantitative PCR analysis showed that the Rac2 gene was expressed in the head kidney, kidney, gill, heart, spleen, liver and muscle, but not in the midgut, of healthy northern snakehead. After infection with Aeromonas veronii, the expression level of Rac2 in different tissues of northern snakehead varied with the time after infection, but in most tissues, Rac2 was upregulated at 36 h after infection. These changes suggested that Rac2 might play an important role in the immune response of northern snakehead against pathogens. The results lay a foundation for further study of the molecular mechanism of northern snakehead immunity against pathogen infection and provide data to support future breeding of related disease-resistant varieties and disease control.