Immune function analysis of LsSd , a transcription factor of the Hippo signaling pathway, in the cigarette beetle Lasioderma serricorne .

The Scalloped (Sd) is a transcription factor that regulates organ size control in the Hippo-signaling pathway. Recent studies have showed that Hippo signaling also functions in the innate immune response. Although the Sd gene has been reported in many insects, their immune functions remain unexplored. In this study, the gene of , with a complete open reading frame that encodes a protein composed of 402 amino acids was identified. was predominantly expressed in early pupae. Tissue-specific analyses revealed that the highest concentrations of were detected in the midgut and brain. At 1-24 h after infection, expression increased substantially. However, expression was downregulated 3-12 h after infection. RNA interference-mediated silencing of the transcript resulted in deformed, considerably smaller, and degenerated wings. Meanwhile, , , and , which are involved in cell proliferation and wing development, were drastically reduced when was depleted. In a survival assay, the knockdown considerably decreased the susceptibility to , a gram-positive bacterium. In addition, knockdown of remarkably downregulated the transcription of in response to stimulation, while upregulating the expression of five immune-related genes. Our results provide conclusive proof for the important roles of in the immune response of .