Abstract: Arginase II(Arg-II)is one kind of arginases.Not only can it participates in the urea cycle, but also has close correlation with pathological process.Here, we determined the whole cDNA sequence of Arg-II gene of ayu(Plecoglossus altivelis)by de-novo transcriptome sequencing of ayu monocytes/macrophages.The results showed that the cDNA sequence of the Arg-II was 4707 nucleotides, containing a large open reading frame that encoded a protein of 348 amino acids with a deduced molecular mass of 38.09 kD and a theoretical isoelectric point(pI)of 6.15.Multiple sequence alignment of complete amino acid sequences showed that ayu Arg-II had the typical characters of Arg-II in animals.Sequence comparison showed that ayu Arg-II shared the highest amino acid sequence identity(85.3%)with that of rainbow trout(Oncorhynchus mykiss).Phylogenetic tree analysis also confirmed that fish Arg-II formed a cluster, and ayu Arg-II was most closely related to that of rainbow trout.Quantitative real-time PCR(qRT-PCR)analysis showed that the mRNA of ayu Arg-II mainly had the expression in liver, brain, head kidney and monocytes/macrophages.Upon Vibrio anguillarum infection, the mRNA expression of gene Arg-II significantly up-regulated in the liver, brain, head kidney and monocytes/macrophages.In summary, our present study revealed a tight relationship between the ayu Arg-II expression and V.anguillarum infection, suggesting that ayu Arg-II plays an important role in fish immune response against bacterial infection.This study provides a theoretical basis for studying the functions of fish Arg-II, and its molecular mechanism in regulating fish immune response to pathogens.

Key words: Plecoglossus altivelis, arginase II, Vibrio anguillarum, monocytes/macrophage, expression