Characterization of pIgR and its association with resistance to iridovirus in Asian seabass

Abstract

The improvement of disease resistance is vital in aquaculture as diseases are one of the serious threats to successful aquaculture. Understanding of molecular mechanisms underlying disease resistance is important in improving resistance against diseases. The pIgR (polymeric immunoglobulin receptor) gene plays an important role in the mucosal immunity of fish. However, not much is known about its roles in inhibiting pathogens in aquaculture species. Here, the pIgR gene from Asian seabass (Lates calcarifer) was characterized, and its functions on the iridovirus infection were examined. LcapIgR consisted of a 2683 bp ORF, a 69 bp 5’ UTR and a 1597 bp 3’ UTR. qRT-PCR revealed that LcapIgR was expressed in all 11 organs examined, being the highest in the heart, followed by intestine, kidney, and eye. Upon a SGIV (Singapore grouper iridovirus) challenge of the fish, the expression of LcapIgR in kidney increased significantly. Overexpression of LcapIgR in an Asian seabass cell line reduced iridovirus entry into cells, and significantly lowered the transcription and replication of the gene encoding for the iridovirus major capsid protein. These results suggest that LcapIgR play an important role in repressing the pathogenic activity of iridovirus. In addition, two SNPs were identified in the 3’ UTR of LcapIgR. Genotyping of both SNPs in survival and dead Asian seabass after challenging with SGIV revealed that both SNPs were possibly associated with resistance to SGIV. Therefore, both SNPs may play a useful role in the selection of fish that are resistant against iridovirus at the fingerling stage.