Abstract
Target of rapamycin (TOR), a serine/threonine protein kinase, is involved in yolk protein synthesis in insects besides regulating a number of growth and developmental processes of an organism. p70 S6 kinase (S6K), a serine/threonine protein kinase, is a downstream target of TOR and an important regulator of protein synthesis responsible for cell growth and reproduction. In the present study, two genes, TOR and S6K were isolated and designated as BdTOR (GenBank accession no. FJ167395) and BdS6K (GQ203802), respectively, from the oriental fruit fly, Bactrocera dorsalis (Hendel). Downregulation of BdTOR activity in vivo resulted in a significant reduction in yolk protein transcripts in both fat body and ovary, with a substantial reduction of ovary size. Downregulation of BdS6K activity in the larval stage resulted in the developmental defects of larvae, pupae, and adults with a curtailed yolk protein expression in the fat body throughout the first reproductive cycle with a substantial reduction in ovary size and also repressed the egg development in female fruit fly. All these observations support the involvement of S6K-mediated TOR signaling in the regulation of the yolk protein synthesis and egg development in B. dorsalis. This study also shows that nutrition-mediated larval S6K signaling is important for adult yolk protein expression and egg production in B. dorsalis. Treatment of the female flies with the reproductive hormone, juvenile hormone (JH), significantly increased BdTOR and BdS6K expression, and also Bdyp1 mRNA only in the presence of BdTOR mRNA, in the fat body, indicating that TOR connects the link between JH and yolk protein production.
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