The promoter of the white spot syndrome virus immediate-early gene WSSV108 is activated by the cellular KLF transcription factor

• WSSV108 has high expression levels throughout the WSSV infection cycle.
• WSSV108 is likely to act as a transcriptional factor.
• WSSV108 promoter has a Krüppel-like factor (KLF) binding site.
• Shrimp KLF plays a major role in WSSV108 promoter activity.
• Silencing of KLF in L. vannamei reduces WSSV108 expression and WSSV replication.

A series of deletion and mutation assays of the white spot syndrome virus (WSSV) immediate-early gene WSSV108 promoter showed that a Krüppel-like factor (KLF) binding site located from −504 to −495 (relative to the transcription start site) is important for the overall level of WSSV108 promoter activity. Electrophoretic mobility shift assays further showed that overexpressed recombinant Penaeus monodon KLF (rPmKLF) formed a specific protein–DNA complex with the 32P-labeled KLF binding site of the WSSV108 promoter, and that higher levels of Litopenaeus vannamei KLF (LvKLF) were expressed in WSSV-infected shrimp. A transactivation assay indicated that the WSSV108 promoter was strongly activated by rPmKLF in a dose-dependent manner. Lastly, we found that specific silencing of LvKLF expression in vivo by dsRNA injection dramatically reduced both WSSV108 expression and WSSV replication. We conclude that shrimp KLF is important for WSSV genome replication and gene expression, and that it binds to the WSSV108 promoter to enhance the expression of this immediate-early gene.