The ammonia transporter gene family and its immune regulatory role in the Pacific oyster (Crassostrea gigas).

Ammonia metabolism disruption critically causes immunosuppression in aquatic animals. This study systematically characterized the ammonia transporter (AMT) gene family and its immune regulatory mechanism in the Pacific oyster (Crassostrea gigas). Through genome-wide screening, four family members were identified, including three ammonium transporters (CgAMT1, CgAMT1-like, and CgAMT3) and one Rhesus blood group-associated A glycoprotein (CgRhAG). All identified proteins contain conserved structural motifs essential for ammonia selectivity, namely the phenylalanine gate and the twin-histidine motif. CgAMTs genes were constitutively expressed across oyster tissues, with CgAMT1 predominantly expressed in haemocytes, suggesting its involvement in immune regulation. Under stimulation with four pathogen-associated molecular patterns (PAMPs), CgAMT1 was significantly upregulated by an average of 2.8-fold. Protein interaction network analysis predicted functional associations between CgAMT1 and MLH1, SLC5A7, and RPS9, which are involved in DNA mismatch repair, ion transport, and protein synthesis, respectively. Long-term Vibrio splendidus stimulation confirmed progressive ammonia accumulation and haemocyte death, with CgAMT1 expression increasing by 7.5-fold and coordinated upregulation of MLH1, SLC5A7, and RPS9. This study identifies a potential ammonia-associated immune cell death mechanism in bivalves, providing molecular targets for aquaculture disease control.