大猿叶虫幼虫期对光周期滞育诱导的分子应答

Diapause is one of the seasonal adaptation strategies in insects. Many insects could enter into diapause in response to environmental cues, e.g., photoperiod and temperature. However, in insects, how to perceive the seasonal environmental cues and interpret these cues to program the diapause in advance is still the most fascinating scientific question. Previous studies indicated that the cabbage beetle, Colaphellus bowringi, could be induced into adult diapause by photoperiod. The sensitive period to photoperiod is larval stage. Clock genes might be involved in photoperiodic diapause induction in the larval stage in this beetle. In current project, based on the transcriptome database of C. bowringi, the molecular events of photoperiodic diapause induction will be studied by using RNA-Seq, qRT-PCR, RACE and RNAi. We are planning to screen the specific expressed genes in the brain tissue of diapause-inducing larvae, analysis the responses of these genes to photoperiodic diapause induction during the larval stage, and determine the functions of key genes responding to photoperiodic signal in diapause induction phase. Then, the upstream molecular events of photoperiodic diapause induction will be uncovered in the cabbage beetle. Our results will help us to clarify the molecular mechanism of photoperiodic diapause induction, expand understanding on the developmental regulation in the field of life, and explore the patterns of insect adaptation and evolution. In addition, these results can provide us useful information to develop new tactics to manage insect pests.

滞育是昆虫的季节性适应策略之一，在昆虫生活史中具有重要意义。虽然环境信号诱导昆虫滞育这种现象为人熟知，但是昆虫感受环境信号进而引发滞育的分子机制仍不清楚，这也是众多生物学家所关注的重要科学问题。申请人的研究表明，大猿叶虫Colaphellus bowringi具有成虫滞育特性，幼虫期可感受光周期的变化而引发成虫滞育，幼虫期的部分光周期钟基因可能参与了滞育诱导。本项目拟以大猿叶虫为对象，依托大猿叶虫转录组数据，采用RNA-Seq、qRT-PCR、RACE和RNAi技术和方法，筛选光周期滞育诱导期幼虫脑组织的差异表达基因，明确滞育诱导期对光周期信号应答的关键基因，鉴定滞育诱导期关键基因的功能，解析大猿叶虫如何感受光周期变化而被诱导进入滞育的分子事件。研究结果不仅可阐明光周期诱导昆虫滞育的分子机制，还有助于深入认识生物发育调控的机制和昆虫适应进化的途径，并可为创新害虫防治技术提供新思路。

提前感知环境变化并进行相应的生长发育是保证昆虫顺利渡过不利季节的重要前提。了解环境信号如何调控昆虫滞育可为研究昆虫季节性适应策略的分子机制提供新见解。本项目以大猿叶虫修水种群为实验材料，首先采用RNA-Seq筛选光周期滞育诱导期幼虫头部的差异表达基因，再利用滞育诱导期的光周期转换、光期遮光和夜间光干扰等试验筛选滞育诱导期对光周期信号应答的基因，最后利用RNAi技术鉴定滞育诱导期关键基因的功能。研究结果指出，生物钟系统、细胞通讯及信号转导相关通路的基因在滞育诱导光周期条件下显著上调表达，并且这些通路中的基因的表达量均可随着光周期的变化而变化。通过比较滞育品系和非滞育品系4日龄幼虫头部中生物钟基因的24h表达模式差异，筛选出clock、cycle、period、timeless、cryptochrome2和vrille可能参与光周期调控大猿叶虫滞育过程。利用RNAi技术证实了上游光周期信号可以通过生物钟基因period和timeless诱导长日照滞育型昆虫滞育的发生，发现period和timeless可能通过larval serum protein 1 α chain、glutenin、trypsin β、ctp synthase、histone H3/H4-like、pyruvate kinase等基因将滞育诱导期所感受的光周期信号逐步转化为下游JH合成信号的过程进而调控滞育，并建立了“光周期信号-period、timeless-Dpp-CBPa-滞育”之间的联系。此外，本项目还发现period和timeless基因可以感知滞育准备期环境中的光周期变化，并通过调控脂肪合成相关基因ADH和FABP、脂肪分解相关基因TGL1的表达进而调控注定滞育个体的脂肪积累，这一过程不依赖于JH信号通路。上述研究结果为解析大猿叶虫如何感受光周期变化而被诱导进入滞育的分子事件提供了重要证据，为深入认识生物发育调控的机制和昆虫适应进化的途径提供了重要理论基础，为创新害虫防治技术提供新思路。