HSP70 and HSP90 are involved in shrimp Penaeus vannamei tolerance to AHPND-causing strain of Vibrio parahaemolyticus after non-lethal heat shock

Acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus carrying toxin producing plasmid, has led to severe mortalities in farmed penaeid shrimp throughout Asia. Previous studies reported that a non-lethal heat shock (NLHS) could enhance disease tolerance in aquatic animals. Here, we investigate whether the NLHS could enhance the survival of shrimp Penaeusvannamei upon challenge with an AHPND-causing strain of V. Parahaemolyticus (VPAHPND). Two NLHS conditions, acute and chronic NLHSs, were used. The former abruptly exposed the juveniles shrimp from 28 degrees C to 38 degrees C for 30 min only once whereas the latter exposed the shrimp to 38 degrees C for 5 min every day for 7 days. The treated shrimp were, then, challenged with VPAHPND at day 3, day 7, and day 30 during the recovery time after the treatment. The results showed that the shrimp exposed to either acute or chronic NLHS had higher survival rate (>50%) than that of the non-heated shrimp control (20%) when they were challenged with VPAHPND at day 3 recovery time. However, only those exposed to chronic NLHS showed the VPAHPND protection at day 7 and day 30 recovery times. Furthermore, the qRT-PCR analysis revealed that the expression of heat shock proteins, LvHSP70, LvHSP90 as well as other immune-related genes, LvproPO and LvCrustin, were induced upon exposure of shrimp to chronic NLHS. Interestingly, gene silencing of LvHSP70 and LvHSP90 eliminated the VPAHPND tolerance in the chronic NLHS shrimp and had decreasing PO activity suggesting that these LvHSPs played crucial roles in bacterial defense in shrimp. All together, we show for the first time that the NLHS enhance the shrimp tolerance to VPAHPND infection and this is likely mediated by the induction of LvHSP70, LvHSP90 and subsequent activation of the proPO system. (C) 2016 Elsevier Ltd. All rights reserved.