Transgenic microRNA-14 rice shows high resistance to rice stem borer.

Rice stem borer (RSB, Chilo suppressalis) is an insect pest that causes huge economic losses every year. Control efforts rely heavily on chemical insecticides, which leads to serious problems such as insecticide resistance, environment pollution, and food safety issues. Therefore, developing alternative pest control methods is an important task. Here, we identified an insect-specific microRNA, miR-14, in RSB, which was predicted to target Spook (Spo) and Ecdysone receptor (EcR) in the ecdysone signalling network. In-vitro dual luciferase assays using HEK293T cells confirmed the interactions of Csu-miR-14 with CsSpo and with CsEcR. Csu-miR-14 exhibited high levels of expression at the end of each larval instar stage, and its expression was negatively correlated with the expression of its two target genes. Overexpression of Csu-miR-14 at the third day of the fifth instar stage led to high mortality and developmental defects in RSB individuals. We produced 35 rice transformants to express miR-14 and found that three lines had a single copy with highly abundant miR-14 mature transcripts. Feeding bioassays using both T0 and T1 generations of transgenic miR-14 rice indicated that at least one line (C#24) showed high resistance to RSB. These results indicated that the approach of miRNAs as targets has potential for improving pest control methods. Moreover, using insect-specific miRNAs rather than protein-encoding genes for pest control may prove benign to non-insect species, and thus is worthy of further exploration.