Identification and Characterization of a Novel fish Phospholipase D1B in olive flounder (Paralichthys oliveceus)

Phospholipase D (PLD) is an important enzyme that plays a pivotal role in the phospholipid metabolism and signaling, including membrane trafficking, cytoskeletal reorganization, receptor-mediated endocytosis, exocytosis, and cell migrationin. In this study, we identified an additional PLD1 gene in the olive flounder (Paralichthys olivaceus), which emerged through fish-specific genome duplication (FSGD), and designated it as PoPLD1B. Notably, the expression pattern of PoPLD1B differs significantly from that of both PoPLD1A and mammalian PLD1 isoforms. PoPLD1B exhibits high expression in digestive organs, including the gullet, pyloric ceca, stomach, and intestine. Furthermore, recombinant PoPLD1B protein, overexpressed using the pCold TF vector, demonstrated phosphatidylcholine (PC)-hydrolyzing activity in the presence of ADP-ribosylation factor 1 (ARF1). Collectively, these findings indicate that ARF1-dependent activation of fish PLD1B plays a crucial role in digestive organs and gill function, particularly in osmotic and ionic regulation, acid-base balance, nitrogenous waste excretion, and calcium ion homeostasis.