Larval RNA interference targeting an appendage patterning gene dachshund in the tortoise beetle Thlaspida biramosa (Boheman) (Coleoptera: Chrysomelidae: Cassidinae)
摘要
Adults of tortoise beetles (Coleoptera: Chrysomelidae: Cassidinae) possess peculiar morphologies, such as explanate margins surrounding their body, tarsal pad for adhesion to the substrate, and long male genitalia that might be evolved via natural and sexual selection. Therefore, tortoise beetles are ideal materials for investigating the developmental mechanisms and evolution of many adaptive traits. This study attempts to evaluate the effectiveness of the RNA interference (RNAi) method for analyzing functions of genes related to the formation of adult morphologies using tortoise beetle species Thlaspida biramosa (Boheman) (Coleoptera: Chrysomelidae: Cassidinae). We inject dsRNA of the well-known appendage patterning gene, dachshund (dac), into the last-instar larvae of T. biramosa. dacRNAi adults exhibited a reduction in number of subsegments of antennae and legs as well as the formation of abnormal grooves on legs. Reduction of appendages has also been known in the previous studies using Drosophila and Tribolium when dac expression was suppressed, suggesting that the RNAi-based dac knockdown was likely to work successfully in T. biramosa. Additionally, this study reveals that the degree of abnormal phenotypes is the same between treatments with 0.1 and 1 µg of dac dsRNA, suggesting high RNAi potential in T. biramosa. Furthermore, there appears to be a specific dsRNA injection timing that maximized RNAi efficiency. Therefore, this study provides the first evidence of the potential for the RNAi-based gene silencing in tortoise beetles. Future studies will be able to analyze genes that cause the unique morphology of tortoise beetles by applying our larval RNAi method.