Proteasome ß3 subunit (PSMB3) controls female reproduction by promoting ecdysteroidogenesis during sexual maturation in Bactrocera dorsalis.

Steroid hormone 20-hydroxyecdysone (20E) plays critical roles in reproductive development in dipterans and several other insect species. Ecdysteroidogenesis in the glands of larval or nymphal insects and other arthropods has been extensively studied, but that in the adult gonads remains largely unknown. Here we identified a proteasome ß3 subunit (PSMB3) from a highly invasive pest Bactrocera dorsalis, and found that this gene was crucial for ecdysone production during female reproduction. PSMB3 was enriched in the ovary, and it was upregulated during sexual maturation. RNAi-mediated depletion of PSMB3 resulted in retarded ovarian development and decreased fecundity. Additionally, knockdown of PSMB3 reduced 20E titer in hemolymph of B. dorsalis. Molecularly, RNA sequencing and qPCR validation revealed that PSMB3 depletion suppressed the expression of 20E biosynthetic genes in the ovary and 20E responsive genes in the ovary and fat body. Furthermore, exogenous 20E rescued the inhibition of the ovarian development caused by PSMB3 depletion. Taken together, this study provides new insights into the adult reproductive development-related biological processes controlled by PSMB3, and proposed a potential eco-friendly control strategy against this notorious agricultural pest.

Small GTPase Rab40C is upregulated by 20-hydroxyecdysone and insulin pathways to regulate ovarian development and fecundity.

The insulin and 20-hydroxyecdysone (20E) pathways coordinately regulate insect vitellogenesis and ovarian development. However, the detailed molecular mechanisms such as the genes mediating the cooperation of the interaction of these 2 pathways in regulating insect reproductive development are not well understood. In the present study, a small GTPase, Rab40C, was identified from the notorious agricultural pest Bactrocera dorsalis. In addition to the well-known RAB domain, it also has a unique SOCS-box domain, which is different from other Rab-GTPases. Moreover, we found that Rab40C was enriched in the ovaries of sexually mature females. RNA interference (RNAi)-mediated knockdown of BdRab40C resulted in a decrease in vitellogenin synthesis, underdeveloped ovaries, and low fertility. Furthermore, depletion of insulin receptor InR or the heterodimer receptor of 20E (EcR or USP) by RNAi significantly decreased the transcription of BdRab40C and resulted in lower fecundity. Further studies revealed that the transcription of BdRab40C could be upregulated by the injection of insulin or 20E. These results indicate that Rab40C participates in the insulin and 20E pathways to coordinately regulate reproduction in B. dorsalis. Our results not only provide new insights into the insulin- and 20E-stimulated regulatory pathways controlling female reproduction in insects but also contribute to the development of potential eco-friendly strategies for pest control.