Regulatory Manner and Role of Circular RNAs in the Microsporidian Invasion of Asian Honeybee

Abstract

Simple Summary Vairimorpha ceranae, a microsporidian fungus that specifically parasitizes the honeybee midgut, impairs nutrient absorption and immune function of bees, thereby posing severe threats to the health of Apis cerana cerana. Circular RNAs (circRNAs) are a class of structurally stable, degradation-resistant non-coding RNAs. Nevertheless, their expression patterns and biological roles during V. ceranae infection in honeybees remain largely elusive. In the present study, high-throughput circRNA sequencing was conducted to comparatively characterize circRNA profiles of purified pathogen spores (uninfected control), as well as microsporidia isolated from honeybee midguts at 7 and 10 days post-infection. The results revealed a dramatic reduction in the total number of microsporidian circRNAs post infection, accompanied by a shift in the dominant circRNA subtype from antisense circRNAs to single-exon circRNAs. Hundreds of differentially expressed circRNAs were identified. CeRNA network prediction indicated that these circRNAs function as endogenous miRNA sponges to sequester microRNAs (miRNAs), indirectly modulating the transcriptional activity of downstream genes associated with energy metabolism and immunity. RT-qPCR validation corroborated the reliability of sequencing data. Key circRNAs including novel_circ_006653 may facilitate the survival and proliferation of pathogens within host bees by regulating host energy supply and immune responses. This study systematically uncovers the dynamic expression patterns and latent regulatory functions of microsporidian circRNAs during host infection for the first time, offering novel molecular targets and theoretical foundations for the prevention and treatment of honeybee microsporidiosis.