MOLECULAR CHARACTERIZATION OF A LONG TYPE PEPTIDOGLYCAN RECOGNITION PROTEIN IN YELLOW CATFISH AND ITS RESPONSE TO EDWARDSIELLA ICTALURI

Peptidoglycan recognition proteins (PGRPs) are a family of pattern recognition receptors (PRRs) of the immune system, exerting the direct antibacterial activity. A long-type PGRP (designated as PfPGRP-L) was identified from yellow catfish, Pelteobagrus fulvidraco. The entire PfPGRP-L cDNA is 1617 bp, including a 135 bp 5'-UTR, a 72 bp 3'-UTR and a 1401 bp open reading frame (ORF). The deduced amino acid sequence of PfPGRP-L with 469 residues showed 60% identity with rainbow trout, Oncorhynchus mykiss PGRP-L. Conserved PGRP domain at the C-terminus was found in PfPGRP-L. Phylogenetic analysis demonstrated that PfPGRP-L was clustered in a same clade with Oncorhynchus mykiss, and formed a long-type PGRP subfamily together with vertebrate PGLYRP2 or PGRP-L members. RT-PCR analysis demonstrated that the mRNA of PfPGRP-L had similar expression patterns, being constitutively expressed in healthy yellow catfish, with the higher expression in intestine and spleen. By real-time PCR analysis, the transcription levels of PfPGRP-L in the liver, spleen, intestine and head kidney were significantly up-regulated after stimulated with Edwardsiella ictaluri. These results suggest that PfPGRP-L is involved in the defensive immune response against bacterial infection.