Trophic microRNA : Post‐transcriptional regulation of target genes and larval development impairment in Plutella xylostella upon precursor and mature microRNA ingestion

Abstract MicroRNAs (miRNAs) are post‐transcriptional gene regulators. In the miRNA pathway's cytoplasmic part, the miRNA is processed from a hairpin‐structured precursor to a double‐stranded (ds) mature RNA and ultimately to a single‐stranded mature miRNA. In insects, ingesting these two ds forms can regulate the target gene expression; this inspired the trophic miRNA's use as a functional genomics and pest management tool. However, systematic studies enabling comparisons of pre‐ and mature forms, dosages, administration times and instar‐wise effects on target transcripts and phenotypes, which can help develop a miRNA administration method, are unavailable due to the different focuses of the previous investigations. We investigated the impact of trophically delivered Px ‐let‐7 miRNA on the lepidopteran pest Plutella xylostella , to compare the efficacies of its pre‐ and ds‐mature forms. Continuous feeding on the miRNA‐supplemented diet suppressed expressions of FTZ‐F1 and E74 , the target ecdysone pathway genes. Both the pre‐let‐7 and mature let‐7 miRNA forms similarly downregulated the target transcripts in all four larval instars. Pre‐let‐7 and let‐7 ingestions decreased larval mass and instar duration and increased mortality in all instars, exhibiting adverse effects on larval growth and development. miRNA processing Dicer‐1 and AGO‐1 's upregulations upon miRNA ingestion denoted the systemic miRNA spread in larval tissues. The scrambled sequence controls did not affect the target transcripts, suggesting the sequence‐specific targeting by the mature miRNA and hairpin cassette's non‐involvement in the target downregulation. This work provides a framework for miRNA and target gene function analyses and potentiates the trophic miRNA's utility in pest management.