Changes in Energy Metabolism Trigger Pupal Diapause Transition of Bactrocera minax After 20-Hydroxyecdysone Application.

Anthony R Clarke,Yong-Cheng Dong,Chang-Ying Niu,Zhen-Zhong Chen

doi:10.3389/fphys.2019.01288

Abstract

Correct timing of diapause entry and exit is critical for a species' survival. While many aspects of insect diapause are well-studied, the mechanisms underlying diapause termination remain largely unknown. The Chinese citrus fly, Bactrocera minax, is a univoltine insect with an obligatory pupal diapause. The application of 20-hydroxyecdysone (20E) is known to terminate diapause in B. minax, and we used this approach, along with isobaric tags for relative and absolute quantitation technology, to determine the proteins associated with diapause termination in this fly. Among 2,258 identified proteins, 1,169 proteins significantly differed at 1, 2, and 5 days post-injection of 20E, compared with the solvent-injected control group. Functional annotation revealed that the majority of differentially expressed proteins were enriched in the core energy metabolism of amino acids, proteins, lipids, and carbohydrates as well as in signal transduction pathways including PPAR signaling, Calcium signaling, Glucagon signaling, VEGF signaling, Ras signaling, cGMP-PKG signaling, and cAMP signaling. A combined transcriptomic and proteomic analysis suggested the involvement of energy metabolism in the response of diapause transition. RNA interference experiments disclosed that a 20E injection triggers diapause termination probably through non-genomic actions, rather than nuclear receptor mediated genomic actions. Our results provide extensive proteomic resources for insect diapause transition and offer a potential for pest control by incapacitating the regulation of diapause termination either by breaking diapause prematurely or by delaying diapause termination to render diapausing individuals at a high risk of mortality.

Highlights

Diapause is a state of developmental arrest evolved by organisms to survive predictable inclement conditions and widely occurs in insects and other invertebrates (Tauber and Tauber, 1976; MacRae, 2010)
In the Rhagoletis pomonella sympatric speciation model, population divergence from the ancestral host plant hawthorn to the new host, apple, is thought to have been facilitated by changes in pupal diapause emergence, which better synchronizes the divergent apple fly populations with apple fruiting (Dambroski and Feder, 2007; Feder et al, 2010)
The results showed that an injection of 20E + dsRNA mixture can trigger an immediate response of diapause termination, which was reflected in a significantly elevated adult emergence within 60 days when compared to the control group [F(3,12) = 29.931, P < 0.001] and nearly overlapped sigmoid curves of adult emergence (Figure 6A)

Summary

Introduction

Diapause is a state of developmental arrest evolved by organisms to survive predictable inclement conditions (notably, but not-exclusively, winter) and widely occurs in insects and other invertebrates (Tauber and Tauber, 1976; MacRae, 2010). On the basis of the decision to enter diapause, insect diapause is traditionally categorized into two types: facultative and obligatory diapause (Tauber and Tauber, 1976; Denlinger, 2002). The diapause switch (entry or exit) is elicited by the perception of environmental cues, commonly photoperiod and temperature, which are subsequently translated into endocrine signals: the concept of neurohormonally regulated diapause ontogenesis (Hodek, 1996; Denlinger, 2002; Denlinger et al, 2005). In the second diapause type, obligatory diapause, diapause is a fixed component of the lifecycle where the “decision” of diapause entry or exit is hardwired, requiring no external diapauseinfluencing cues (Denlinger et al, 2005; Koštál et al, 2016)

Methods

Discussion

Conclusion