RNAi and Antiviral Defense in the Honey Bee.

Laura M Brutscher,Michelle L Flenniken

doi:10.1155/2015/941897

Abstract

Honey bees play an important agricultural and ecological role as pollinators of numerous agricultural crops and other plant species. Therefore, investigating the factors associated with high annual losses of honey bee colonies in the US is an important and active area of research. Pathogen incidence and abundance correlate with Colony Collapse Disorder- (CCD-) affected colonies in the US and colony losses in the US and in some European countries. Honey bees are readily infected by single-stranded positive sense RNA viruses. Largely dependent on the host immune response, virus infections can either remain asymptomatic or result in deformities, paralysis, or death of adults or larvae. RNA interference (RNAi) is an important antiviral defense mechanism in insects, including honey bees. Herein, we review the role of RNAi in honey bee antiviral defense and highlight some parallels between insect and mammalian immune systems. A more thorough understanding of the role of pathogens on honey bee health and the immune mechanisms bees utilize to combat infectious agents may lead to the development of strategies that enhance honey bee health and result in the discovery of additional mechanisms of immunity in metazoans.

Highlights

Honey bees (Apis mellifera) contribute vital pollination services to agricultural crops and native landscapes, accounting for over $15 billion/year in economic value in the US [1]
Multiple mechanisms are involved in insect immune responses, including phagocytosis, melanization, and signal transduction of the Toll, Imd, and Jak/STAT (Janus kinase and Signal Transducer and Activator of Transcription) innate immune response pathways which result in the production of antimicrobial peptides (AMPs) and other effector proteins
Pathogen incidence and abundance correlate with Colony Collapse Disorder (CCD), as well as colony health and loss in multiple studies

Summary

Introduction

Honey bees (Apis mellifera) contribute vital pollination services to agricultural crops and native landscapes, accounting for over $15 billion/year in economic value in the US [1]. In the US, colony mortalities are partially attributed to Colony Collapse Disorder (CCD) [14,15,16,17,18,19] These losses have stimulated greater interest in investigating honey bee biology, including the role of pathogens in colony mortalities and the role of the RNA interference (RNAi) mechanism in honey bee antiviral defense. While experimental introduction of virus sequence-specific dsRNA reduced honey bee virus infections in adults and larvae [29, 34,35,36,37,38,39], introduction of non-sequence-specific dsRNA resulted in virus reduction and altered gene expression [38] This is consistent with global changes in honey bee gene expression, including untargeted genes (i.e., off-target effects), observed from administration of dsRNA [40, 41]. We discuss RNAi as a tool for gene knockdown in honey bees, the role of the siRNA pathway of RNAi in honey bee antiviral defense, and additional honey bee antiviral defense pathways, including evidence of a non-sequence-specific dsRNA-stimulated immune pathway in honey bees

RNA Silencing

RNAi-Mediated Knockdown of Endogenous Gene Expression

RNAi in Antiviral Defense

Additional Antiviral Defense Mechanisms

Nonspecific dsRNA Triggered Virus Reduction

Conclusion