Abstract:β-defensins are cysteine, cationic, antibacterial peptides that play very important roles in the vertebrate immune system. In this study, the cDNA fragment of β-defensin gene from Acipenser gueldenstaedti was cloned using a PCR method based on the Solexa sequencing results of gonad transcriptome, and gene expression was performed by qRT-PCR. The results showed that cDNA of β-defensin was 333 bp in length and contained an open reading frame (ORF) with 213 bp, which was deduced to encode a precursor peptide of 71 amino acids consisting of a signal peptide of 23 amino acid residues and a mature peptide of 48 amino acid residues. Russian sturgeon β-defensin possessed six conserved cysteine residues, forming three disulfide bridges at C38~C66, C44~C60 and C48~C67, and containing 1 defensin-β-2 domain. This structure is very similar to other species and conserved in evolution. Homologous alignment revealed that Russian sturgeon β-defensin had the highest sequence identity with fish species, about 54%~60%. qRT-PCR analysis showed the β-defensin transcript is constitutively expressed in 11 tissues (liver, intestine, spleen, head-kidney, gill, blood, brain, skin, muscle and gonad, stomach) in healthy fish, with highest expression in the gonads and skin. Artificial infection of A. gueldenstaedti with Aeromonas hydrophila resulted in a significantly upregulated expression in the intestine, spleen, head kidney, blood, and gill while downregulating expression in the liver. The most significant upregulated expression and the peak level at 72 h reached 700 times baseline in the head-kidney. The results indicate Acipenser gueldenstaedti β-defensin genes are involved in the immune response.
