Point mutations of Dicer2 conferred Fusarium asiaticum resistance to RNAi-related biopesticide

The use of RNA interference (RNAi) technology to control pests is explored by researchers globally. Even though RNA is a new class of pest control compound unlike conventional chemical pesticides, the evolution of pest resistance needs to be considered. Here, we first investigate RNAi-based biopesticide resistance of Fusarium asiaticum, which is responsible for devastating diseases of plants, for example, Fusarium head blight. Five resistant strains were isolated from 500 strains that treated with UV-mutagenesis. The mutation common to all of the five resistant mutants occurred in the gene encoding Dicer2 (point mutations at codon 1005 and 1007), which were under strong purifying selection pressure. To confirm whether the mutations in Dicer2 confer resistance to RNAi, we exchanged the Dicer2 locus between the sensitive strain and the resistant strain by homologous double exchange. The transformed mutants, Dicer2^R1005D and Dicer2^E1007H, exhibited resistance to dsRNA in vitro. Further study showed that mutations of R1005D and E1007H affected the intramolecular interactions of Dicer2, resulting in the dysfunction of RNase III domain of Dicer2. The amount of sRNAs produced by Dicer2^R1005D and Dicer2^E1007H was extremely reduced along with variation of sRNA length. Together, these findings revealed a new potential mechanism of RNAi resistance and provided insight into RNAi-related biopesticide deployment for fungal control.