Molecular cloning and expression analysis of aspartate aminotransferase (AST) in Penaeus monodon under ambi-ent ammonia stress

To explore the function of aspartate aminotransferase gene in the process of the ammonia nitrogen metabolism of black tiger shrimps (Penaeus monodon), the full-length cDNA sequence of aspartate aminotransferase from P.monodon (PmAST) was obtained by high throughput transcriptome sequencing and rapid amplification of cDNA ends.On this basis, the expression of the PmAST in different tissues under different ambient ammonia stress were detected by fluorescence-quantitative real time PCR.The cDNA length of PmAST was 1 957 bp, including a 5′UTR of 131 bp and a 3′UTR of 584 bp.The length of the open reading frame (ORF) was 1 242 bp encoding a polypeptide of 413 amino acid.The molecular mass of the deduced amino acid (aa) sequence was 45.852 kD with an estimated pI of 8.85, and there was a tailing signal (poly A) with 30 bp length.Like other animals′ ASTs, the structure of PmAST protein included an AAT-I superfamily domain.There were 15 phosphorylation sites and 2 glycosylation sites in this protein.Analysis of the tissue expression pattern of the PmAST shows that PmAST mRNA was expressed in all tested tissues, including ovary, haemolymph, brain, lymph, stomach, muscle, thoracic ganglia, heart, hepatopancreas and gill.The PmAST expression reached the maximum value in hepatopancreas and was the lowest in brain.After ambient ammonia stress experiment, the expression of the PmAST in hepatopancreas and gill was significantly higher than that in the control (P < 0.05), and the expression profiles differed between hepatopancreas and gill.The result shows that the higher the ambient ammonia concentration is, the greater the increase of PmAST expression will be.Therefore, the PmAST takes part in acute ammonia stress.