The purpose is to study Litopenaeus vannamei transcription factor AP-1 potential role in the immune response triggered by the virus.Our previous transcriptome results showed that the expression profile of AP-1 fluctuated significantly in response to WSSV infection.In this research,a novel AP-1 gene(GenBank Accession Number:KF999956)was cloned from Pacific white shrimp(L.vannamei).The full length cDNA of AP-1 has an 882bp ORF encoding 293 amino acids.The predicted molecular weight and calculated isoelectric point of AP-1 was 32.7 KDa and 7.80.The online software(SMART)analysis results showed that two predicted domains including the Jun protein domain and a highly conserved basic leucine zipper(bZIP)which existed in the deduced protein of AP-1.Multiple alignment analysis shows that AP-1 shared 48%,42% and 43% amino acid identities with Ixodes Scapularis,Mus musculus and Homo sapiens,respectively.Tissue expression analysis by Semi-quantitative RT-PCR revealed that expression of AP-1 gene is constitutive in all selected tissues and shows highest expression in hemocytes.The transcript of AP-1 is induced in response to white spot syndrome virus(WSSV)infection.At the early stage of WSSV infection(0.5 hpi),AP-1 did not change significantly.Then the expression of AP-1 gene began to increase after 5 hpi.At 24 hpi,the gene expression increased significantly and reached the highest level(P<0.01).From this result,it could be deduced that AP-1 gene took part in shrimp innate immune response caused by WSSV.