AUTHOR=McMenamin Alexander J. , Brutscher Laura M. , Daughenbaugh Katie F. , Flenniken Michelle L. 

TITLE=The Honey Bee Gene Bee Antiviral Protein-1 Is a Taxonomically Restricted Antiviral Immune Gene

JOURNAL=Frontiers in Insect Science

VOLUME=1

YEAR=2021

URL=https://www.frontiersin.org/journals/insect-science/articles/10.3389/finsc.2021.749781

DOI=10.3389/finsc.2021.749781

ISSN=2673-8600

ABSTRACT=<p>Insects have evolved a wide range of strategies to combat invading pathogens, including viruses. Genes that encode proteins involved in immune responses often evolve under positive selection due to their co-evolution with pathogens. Insect antiviral defense includes the RNA interference (RNAi) mechanism, which is triggered by recognition of non-self, virally produced, double-stranded RNAs. Indeed, insect RNAi genes (e.g., <italic>dicer</italic> and <italic>argonaute-2</italic>) are under high selective pressure. Honey bees (<italic>Apis mellifera</italic>) are eusocial insects that respond to viral infections <italic>via</italic> both sequence specific RNAi and a non-sequence specific dsRNA triggered pathway, which is less well-characterized. A transcriptome-level study of virus-infected and/or dsRNA-treated honey bees revealed increased expression of a novel antiviral gene, GenBank: <ext-link ext-link-type="DDBJ/EMBL/GenBank" xlink:href="MF116383" xmlns:xlink="http://www.w3.org/1999/xlink">MF116383</ext-link>, and <italic>in vivo</italic> experiments confirmed its antiviral function. Due to <italic>in silico</italic> annotation and sequence similarity, MF116383 was originally annotated as a probable <italic>cyclin-dependent serine/threonine-protein kinase</italic>. In this study, we confirmed that MF116383 limits virus infection, and carried out further bioinformatic and phylogenetic analyses to better characterize this important gene—which we renamed <italic>bee antiviral protein-1</italic> (<italic>bap1</italic>). Phylogenetic analysis revealed that <italic>bap1</italic> is taxonomically restricted to Hymenoptera and <italic>Blatella germanica</italic> (the German cockroach) and that the majority of <italic>bap1</italic> amino acids are evolving under neutral selection. This is in-line with the results from structural prediction tools that indicate Bap1 is a highly disordered protein, which likely has relaxed structural constraints. Assessment of honey bee gene expression using a weighted gene correlation network analysis revealed that <italic>bap1</italic> expression was highly correlated with several immune genes—most notably <italic>argonaute-2</italic>. The coexpression of <italic>bap1</italic> and <italic>argonaute-2</italic> was confirmed in an independent dataset that accounted for the effect of virus abundance. Together, these data demonstrate that <italic>bap1</italic> is a taxonomically restricted, rapidly evolving antiviral immune gene. Future work will determine the role of <italic>bap1</italic> in limiting replication of other viruses and examine the signal cascade responsible for regulating the expression of <italic>bap1</italic> and other honey bee antiviral defense genes, including coexpressed <italic>ago-2</italic>, and determine whether the virus limiting function of <italic>bap1</italic> acts in parallel or in tandem with RNAi.</p>