Nonfunctional ingestion of plant miRNAs in silkworm revealed by digital droplet PCR and transcriptome analysis

Since a plant miRNA (miR168) cross-regulating a mammalian transcript was reported, miRNA-mediated cross-kingdom communication has become one of the most compelling but controversial topics. In the present study, we used silkworm and mulberry, which is a model for studies on the interactions between the insect and its host plant, to address whether miRNA-mediated cross-kingdom communication is a common phenomenon. The results of TA clone, Sanger sequencing and droplet digital PCR demonstrated that several mulberry-derived miRNAs could enter to silkworm hemolymph and multiple tested tissues. Synthetic miR166b was also detected in hemolymph and fat body. However, the ingestion of synthetic miR166b did not play roles in silkworm physiological progress, which was revealed by RNA-seq analyses, RT-PCR, and phenotypic investigations. Mulberry miRNAs are convincingly transferred to the silkworm orally and no physiological process associated with the miRNAs was demonstrable. The results provided a new aspect of cross-kingdom miRNA transfer.