Comparative Gene Expression Patterns of Two EcobNPV Strains in Ectropis grisescens Revealed by Transcriptome Analysis

Ectropis obliqua nucleopolyhedrovirus (EcobNPV) is an important biocontrol agent against Ectropis obliqua and E. grisescens. A previously isolated strain, EcobNPV-QF4, exhibits significantly higher virulence than the original strain EcobNPV-QV, yet the molecular basis for this difference remains unclear. Leaf-dipping bioassays demonstrated that EcobNPV-QF4 caused significantly higher larval mortality than EcobNPV-QV from 10 dpi onward, reaching 97.9% versus 33.8% at 16 dpi, and higher pupal mortality (100% versus 47.3%), confirming its superior virulence across both larval and pupal stages. To investigate the transcriptional dynamics underlying virulence variation, we performed a comparative time-course transcriptomic analysis of E. grisescens infected with either strain at 0, 2, 6, 12, 24, 36, and 48 h post-infection. The reliability of the RNA-seq data was validated by qRT-PCR for selected expressed genes. The results showed that, relative to EcobNPV-QV, the EcobNPV-QF4 strain exhibits a transcriptional strategy characterized by comprehensive and accelerated activation: the transcriptional initiation of its functional modules is globally advanced by approximately 6 h compared with EcobNPV-QV, and genes associated with midgut escape, virion assembly, and viral DNA replication are preferentially and coordinately expressed, resulting in a more synchronized transcriptional profile. Based on these findings, we hypothesize that the enhanced virulence of EcobNPV-QF4 is not attributable to a single factor but rather reflects a synergistic, multitiered acceleration of transcriptional progression that may compress the infection cycle and enhance viral dissemination efficiency. These findings provide critical insights into the molecular mechanisms that may underlie baculovirus virulence and provide a basis for future mechanistic studies.