Influence of Spodoptera littoralis Multiple Nucleopolyhedrovirus miRNAs on Spodoptera littoralis Gene Transcription Regulation Associated with Apoptotic Pathway

MicroRNAs (miRNAs) are evolutionarily conserved RNAs that play a crucial role in the apoptotic process in insects. In this study, the transcriptional regulation of eight apoptotic-related genes (Fas1, Fas2, Caspase 8, Caspase 5, COX1, Apaf1, Dronc and Effector Caspase-1) in Spodoptera littoralis was analyzed. Using in silico prediction tools, 43 novel miRNAs were predicted to be encoded by Spodoptera littoralis nucleopolyhedrovirus (SpliMNPV). Of these, seven putative SpliMNPV miRNAs targeting the detected apoptotic genes were validated by quantitative real-time PCR (qPCR) after S. littoralis infection with SpliMNPV at different time points: 24, 48 and 72 h post-infection (hpi). Four miRNAs (miR1402, miR94, miR638 and miR749) were found to be unique to SpliMNPV. Gene expression analysis revealed that most of the S. littoralis apoptotic target genes were downregulated by viral miRNAs during SpliMNPV infection. The Dronc gene exhibited the highest level of downregulation at 72 hpi. In contrast, COX1 gene expression was upregulated at 48 and 72 hpi, respectively. Additionally, Apaf1 gene expression showed a positive correlation with most apoptotic target genes, whereas COX1 expression exhibited a negative correlation with Dronc, Effector Caspase-1, Fas1 and Fas2 gene expression. These findings suggest that the identified SpliMNPV miRNAs significantly influence the transcriptional regulation of S. littoralis apoptotic-related genes in response to viral infection.