Ammonia Nitrogen Promotes White Spot Syndrome Virus Infection In Marsupenaeus Japonicus By Inducing Heat Shock Factor 1

As an important economic industry,shrimp aquaculture occupies an important position in the national economy.However,with the rapid development of shrimp aquaculture,the deterioration of aquaculture environment and diseases have gradually emerged.Disease outbreaks are usually the result of the interaction of pathogen,host and environment.White Spot syndrome virus(WSSV)is the main virus affecting shrimp aquaculture,and has caused huge economic losses.To date,there is still no effective controlling method for WSSV,and early prevention is considered as an important means of preventing outbreaks of the virus.Ammonia nitrogen is the main environmental stress factor in aquaculture.Studies have found that increased ammonia nitrogen concentration in water will reduce the survival rate of shrimp infected with WSSV,but the biological mechanism behind this is not clear.In this study,we used Marsupenaeus japonicus as experimental animal and found that the virus replication level in shrimp which were treated with ammonia nitrogen stress was significantly higher than that in untreated group.We found Heat shock factor 1(Hsf1)might be an important transcription factor in this process.Hsf1 expression in shrimp hemocytes and gills was significantly increased after ammonia treatment.After RNAi knockdown of Hsf1 expression,the phenomenon that ammonia nitrogen stress promoted WSSV infection disappeared.These results indicated that Hsf1 played an important role in promoting WSSV infection under ammonia nitrogen stress.Further mechanistic studies found that Hsf1 promoted WSSV infection in two ways.On one hand,Hsf1 can directly bind to the Heat shock response element(HSE)in the promoter region of WSSV Immediate early(IE)gene to promote the transcription of IE gene,thus promoting virus replication.Hsf1.on the other hand,suppresses host antiviral ability by directly regulating the transcription of two negative immune-regulatory factors,Cactus and Socs-2,inhibiting the transcription factors Dorsal and Stat,respectively,and further inhibiting the expression of the downstream antiviral cytokine MjVago-L and other antiviral peptides.This study also found that Hsf1 was activated by mitogen-activated protein kinase p38 under ammonia nitrogen stress.When p38 activity was inhibited.the phosphorylation level of Ser326 on Hsf1 and its promoting effect on WSSV infection were also significantly inhibited.Therefore,this study revealed the specific mechanism that ammonia stress promoted WSSV infection through inducing and activating Hsf1,and provided basis for disease control in shrimp aquaculture.