Involvement of Met and Kr-h1 in JH-Mediated Reproduction of Female Bactrocera dorsalis (Hendel)

Abstract

Juvenile hormone (JH) prevents metamorphosis during insect larval stages and promotes adult reproductive processes. Krüppel-homolog 1 (Kr-h1), a zinc finger transcription factor assumed to be induced by JH via the JH receptor methoprene-tolerant (Met), mediates the antimetamorphic effect of JH in insects, but its function in JH-mediated reproductive processes has not been fully explored. In this study, <i>Met</i> and <i>Kr-h1</i> involved in the JH signaling pathway were first cloned and identified from the oriental fruit fly, <i>Bactrocera dorsalis</i>, an important pest infesting fruit and vegetables worldwide. Subsequent spatiotemporal expression analysis revealed that <i>Met</i> and <i>Kr-h1</i> were both highly expressed in 7-day-old adults and fat body of female adults, respectively. Treatment with a JH analog (methoprene) significantly induced the expression of JH signaling and <i>vitellogenin</i> (<i>Vg</i>) genes and accelerated ovary development. RNA interference (RNAi) further revealed that either <i>Met</i> or <i>Kr-h1</i> depletion at the adult stage of <i>B. dorsalis</i> impeded ovary development, with significantly lower egg production noted as well. In addition, rescue through methoprene application after RNAi stimulated the expression of JH signaling and <i>Vg</i> genes. Although there were still differences in ovary phenotype between rescued insects and the pre-RNAi control, ovary redevelopment with a larger surface area was observed, consistent with the spatiotemporal expression and phenotypes recorded in the original methoprene experiment. Our data reveal the involvement of Met and <i>Kr-h1</i> in insect vitellogenesis and egg production, thus indicating the crucial role of the JH signaling pathway in insect reproduction.