粘虫飞行促进生殖的保幼激素调控机制

The oriental armyworm, Mythimna separata, is a typical devastating, worldwide long-distance migratory crop pest. In this species, we discovered that flight accelerates and synchronizes reproduction, resulting in population outbreaks during an appropriate migratory scenario. However, the regulatory mechanism remains unknown. Now we have evidences that juvenile hormone (JH) regulates adult migration and reproduction in M. separata. Based on these foundations, we hypothesize that flights influence dynamic JH concentrations during migration by regulating expression of critical genes in JH synthesis and degradation pathways. Furthermore, we hypothesize further that flights also directly or indirectly regulate the critical genes during JH regulation reproduction pathway, such as JH receptor. Flight accelerates and synchronizes adult reproduction by the whole JH regulatory pathway from JH synthesis and degradation to JH regulation reproduction pathway. We will test our hypotheses in this project, by investigating the mechanism of JH regulation of reproductive physiology. Our objectives are (1) clarify how JH titer is affected by flight using HPLC; (2) determine the influence of JH on development and energy resource allocation of flight muscle and ovary, flight and reproductive capacity, by using topical applications of JH analogue (JHA), which mimics JH actions and precocene II, which blocks JH synthesis; (3) determine the effects of flight on expression patterns of genes mediating JH synthesis and degradation and reproduction regulation, including allatotropin (AT), allatostatin (AST) and juvenile hormone esterase (JHE), the probable JH receptor methoprene-tolerant (Met) and vitellogenin (Vg) by using real time PCR; and (4) use RNAi gene silence tools to confirm the roles of AT, AST, JHE and Met in flight-driven reproduction acceleration. This project will be helpful to clarify the regulation mechanism of JH during an appropriate flight scenario optimizing reproduction, and provide new knowledge on the mechanism of oriental armyworm migration and population outbreaks that can be applied to substantially improve population forecasting.

粘虫是一种典型远距离迁飞害虫，前期已明确成虫在适宜模式下飞行促进生殖并导致成灾，但产生这一特性的调控机制尚不清楚。申请人在获得保幼激素（JH）参与调控粘虫飞行和生殖证据的基础上，提出飞行通过调控JH合成代谢及其生殖途径的相关基因来促进生殖的假说并由本项目研究予以验证。通过HPLC测定飞行促进生殖中的JH变化，结合JH类似物（JHA）和抗JH的早熟素点滴检测JH对卵巢和飞行肌发育及其能源物质动用、飞行与生殖能力的影响，明确JH在飞行促进生殖中的功能；进一步分析JH合成代谢相关的促咽侧体素（AT）、咽侧体抑制素（AST）、保幼激素酯酶（JHE）和JH受体Met以及卵黄原蛋白（Vg）基因在飞行促进生殖中的表达谱，结合RNAi鉴定AT、AST、JHE和Met在飞行促进生殖调控途径中的功能，从而揭示JH在飞行促进生殖模式中的调控机制。为阐明粘虫迁飞致灾的生理与分子机制及提高其预测预报水平提供新思路。

本项目以一种典型的远距离迁飞危害的重大农业害虫粘虫为研究对象，围绕其迁飞致灾的内在机制开展研究。通过明确飞行夜晚数对粘虫生殖的不同影响，揭示了明确了迁飞促进粘虫生殖的最佳飞行模式，羽化后1日龄起飞，飞行2个夜晚以内显著促进生殖，飞行4-5个夜晚则显著抑制生殖；揭示了JH在迁飞调控生殖中的主要功能，促进生殖的飞行导致JH上升，抑制生殖的飞行则导致JH下降，羽化后1日龄是JH调控粘虫迁飞和生殖的关键时期；解析了JH调控粘虫生殖的分子机制，明确了保幼激素（JH）调控通路中4种关键基因促咽侧体神经肽（AT）、咽侧体抑制神经肽（AST）、保幼激素酯酶（JHE）和受体（Met）基因的时空表达模式，揭示了在促进/抑制粘虫生殖两种飞行模式下4种基因时空表达情况，明确了飞行通过调节JH通路上关键基因的表达，从而调控生殖；揭示了AT和Met基因对粘虫生殖的重要调控作用，Met基因是飞行影响生殖过程中JH调控通路上的关键受体，JH通过和粘虫体内受体Met结合从而达到促进Vg沉积、加速卵巢发育和生殖的作用。当Met基因被抑制后，飞行引起的JH信号被阻断，导致促进粘虫生殖的飞行无法恢复其下游的kr-h1、Vg基因的表达，因此卵巢发育进度减缓，生殖被抑制；在此基础上，系统揭示了飞行促进粘虫生殖的JH调控机制，成虫在羽化后1日龄起飞，连续飞行2个夜晚后引起促进脑分泌的AT表达量升高，从而刺激咽侧体CA加速合成JH，升高的JH与卵巢的Met结合后，引起其下游的kr-h1和调控粘虫卵巢发育的vg基因表达量的升高，从而加速卵巢发育，导致产卵提前，产卵量显著上升；同时，升高的JH和飞行肌上的Met结合后，引起飞行肌的提前降解，导致飞行能力下降，能源物质分配由飞行转向生殖。