Abstract

The blood clam ( Tegillarca granosa ) is a mudflat shellfish with a high economic value in the aquaculture industry. The IL-17D homologous sequence ( TgIL-17D ) has been identified in the blood clam genome to be involved in the immune and inflammatory response to Vibrio infection. This study aimed to clone the full length of TgIL-17D cDNA, characterize its protein structure, and construct the evolutionary phylogenetic tree to reveal the intrinsic relationship of TgIL-17D to those of other species. The binding site of TgAP-1 protein in the TgIL-17D promoter was successfully predicted to assess their interaction. In order to investigate the molecular mechanism of TgAP-1 and TgIL-17D pathways after Vibrio infection, the changes in the expression of apoptotic and inflammatory genes after TgAP-1 knockdown were analyzed. Moreover, the changes in physiological metabolism and the death level were examined to evaluate the effect of TgAP-1-TgIL-17D pathway blockade on the resistance of blood clams to Vibrio infection. The data showed that full-length TgIL-17D cDNA is 1587 bp with an open-reading frame of 594 bp and encodes a 197-amino-acid polypeptide with a molecular mass of 22.0 kDa. TgIL-17D and its protein were ubiquitously detected in all six tissues tested, especially in the gills. Furthermore, the predicted presence of TgAP-1 binding sites in the TgIL-17D promotor was confirmed in this study by electrophoretic mobility shift (EMSA) assays and chromatin-immunoprecipitation (ChIP) assays. Finally, knockdown of TgAP-1 via RNA interference (RNAi) was shown to protect blood clams from large-scale death upon Vibrio challenge by alleviating inflammation and tissue damage. In conclusion, the data obtained in this study suggest that low expression levels of TgAP-1 and TgIL-17D may improve the Vibrio resistance of blood clams. TgAP-1 plays an important role in TgIL-17D expression.