Dual function of the Tuta absoluta 3-phosphoinositide-dependent protein kinase-1 in pupa ecdysis and adult reproduction

Phosphoinositide-dependent kinase PDK, a key component of the insulin signaling pathway, plays an important role in the regulation of insect growth and development. However, the functional significance of the PDK gene in Tuta absoluta, a destructive invasive tomato leaf miner, remains unknown. In this study, we identified and characterized a PDK gene (designated TaPDK) and analyzed its physiological roles in molting and reproduction of T. absoluta. Our results showed that the TaPDK expression levels were elevated in the 5- and 6-day-old pupae before ecdysis and declined immediately after eclosion. TaPDK was predominantly expressed in the head, midgut and abdomen. When the TaPDK was knockdown, the larval-pupal molting and female reproduction were severely affected. Injecting dsRNA of TaPDK into 2-day-old female pupae resulted in severe phenotypic changes (cuticular shrinkage) in 31.29% of pupae, ultimately leading to death. Knockdown of TaPDK significantly reduced the 20E titer and chitin content and downregulated the expression levels of genes involved in the 20E pathway and chitin metabolism. Further investigation revealed that the suppression of TaPDK impaired ovarian development, resulting in significantly reduced fecundity and hatchability. In addition, the JH titer and vitellogenin content of TaPDK-deficient females were reduced, and the expression of Vg, VgR, and JH signaling pathway genes were significantly decreased. Collectively, our study provides a deep insight into the PDK-mediated regulation of pupal ecdysis and female reproduction in T. absoluta.