In silico identification of off-target pesticidal dsRNA binding in honey bees (Apis mellifera)

Background

Pesticidal RNAs that silence critical gene function have great potential in pest management, but the benefits of this technology must be weighed against non-target organism risks.

Methods

Published studies that developed pesticidal double stranded RNAs (dsRNAs) were collated into a database. The target gene sequences for these pesticidal RNAs were determined, and the degree of similarity with sequences in the honey bee genome were evaluated statistically.

Results

We identified 101 insecticidal RNAs sharing high sequence similarity with genomic regions in honey bees. The likelihood that off-target sequences were similar increased with the number of nucleotides in the dsRNA molecule. The similarities of non-target genes to the pesticidal RNA was unaffected by taxonomic relatedness of the target insect to honey bees, contrary to previous assertions. Gene groups active during honey bee development had disproportionately high sequence similarity with pesticidal RNAs relative to other areas of the genome.

Discussion

Although sequence similarity does not itself guarantee a significant phenotypic effect in honey bees by the primary dsRNA, in silico screening may help to identify appropriate experimental endpoints within a risk assessment framework for pesticidal RNAi.

Destruxin A Induces and Binds HSPs in Bombyx mori Bm12 Cells

Destruxin A (DA) is a cyclodepsipeptidic mycotoxin isolated from the entomopathogenic fungus, Metarhizium anisopliae. It has insecticidal activity against host insect's innate immunity system, but the molecular mechanism is not yet elucidated. In our previous experiment, four HSPs (heat shock proteins, BmHSP70-3, BmHSP75, BmHSP83, and BmHSCP) were characterized from the specific protein electrophoretic bands of Bombyx mori Bm12 cell line treated with DA in the test of drug affinity responsive target stability (DARTS), which implied that these HSPs might be kinds of DA-affinity proteins, or DA induces them up-regulated expression. Therefore, in current research, the interactions of DA and HSPs were explored through analysis of bio-layer interferometry (BLI) employing FortBio OcteteQK. The expression levels of HSPs genes were surveyed by quantitative real-time polymerase chain reaction (qPCR). The results indicated that DA had no interactions with BmHSP70-3, BmHSP75, and BmHSP83, but had affinity to BmHSCP with a K_D value of 88.1 μM, in BLI analysis. However, the expression levels of all HSPs genes were significantly up-regulated after the Bm12 cells were treated by DA. In conclusion, DA can induce the four HSPs expression in Bm12 cells, but DA only binds to BmHSCP. Our research provides new insights on understanding of the action mechanisms of destruxins.