保幼激素在二化螟“两头下注”生态策略的作用及分子机制

Widely distributed striped stem borers, Chilo suppressalis, are a group of important pests of rice. In addition to the increasing resistance to pesticide in the field, the stem borers have also utilized a conservative ecological strategy of "bet hedging" demonstrating multiple emergence peaks and longer duration phase of each generation. This strategy makes the chemical management of the pest more difficult. The variation of development rate among individual larvae is beneficial to stabilization of the field populations, however, the molecular mechanism about it is still unknown so far. This project will focus on the juvenile hormone (JH) of C. suppressalis, analyses the relationship between JH titer and daily weight of larvae, reveal the effects on the development process via over-expression or knockdown the JH. The miRNA level analysis will allow for the relevance of miRNA and its target genes on JH synthesis pathway and signal pathway, such as functional analysis of interference and over-expression of miRNAs. The internal mechanism component of the project will develop a deep understanding of the variation of development rate in C. suppressalis. Based on the research, a groundbreaking understanding of the"bet hedging" stratege of C. suppressalis will be developed to help figure out a new efficient control point of C. suppressalis and weaken the utilization of bet hedging strategy with shorter occurrence duration. Ultimately, this study could contribute to regional sustainable management of C. suppressalis.

二化螟分布非常广泛，是水稻重要害虫。除了日益严峻的抗药性问题，田间二化螟还呈现每代蛾峰多、发蛾持续时间长的保守型“两头下注”生态策略，严重影响防治适期选择和施药效果。二化螟幼虫个体间发育历期不一致的发育异步化现象，利于种群维持，但其分子机制研究尚不明确。本项目以保幼激素为切入点，测定二化螟幼虫阶段逐日体重与JH滴度相关性，过表达或敲低JH对幼虫发育进程的影响，通过miRNA水平解析该调控作用，探明作用于保幼激素合成通路及下游应答通路基因的miRNA与靶基因的关系，进一步利用干扰及过表达miRNA进行功能分析，阐明miRNA调控二化螟发育历期差异化的分子机制。预期明确二化螟新的有效控制点，削弱其对“两头下注”策略的应用，缩短螟蛾发生期，从而减少田间用药，延缓抗性问题，为二化螟绿色防控及可持续治理提供新视角。

二化螟是重要的水稻害虫。除了日益严峻的抗药性问题，田间二化螟还呈现每代蛾峰多、发蛾持续时间长的保守型“两头下注”生态策略，严重影响防治适期选择和施药效果。这种幼虫个体间发育历期差异大，利于种群维持，其机制研究尚不明确。本研究首先进行室内分离实验，结果显示分子遗传占比小于 10%，并利用ddRADseq技术挖掘候选基因。其次通过大量观测二化螟幼虫个体发育进程，发现三龄后期是个体体重分化的关键时期；第13日的体重与幼虫历期呈较高的负相关性（R=-0.640）；且通过JH类似物处理后个体间差异变小。通过mRNA和miRNA比较转录组测序，生物信息学预测挖掘作用于JH合成、降解及信号转导通路上靶基因的miRNA，并进行了克隆。继而，分析了JH通路上的CsMet基因功能，结构预测CsMet是一种bHLH-PAS转录因子，其时空表达特征呈现出与JH滴度在幼虫期每一龄初期有短时上升的一致模式，表明JH能够激发CsMet的转录，幼虫JHA处理后显著延长了发育历期，临界体重增加；幼虫经dsCsMet处理后明显抑制了生长，临界体重低于对照。此外，研究发现水稻tps46催化的挥发性产物Eβf通过破坏昆虫JH平衡，抑制了二化螟幼虫的发育，显著增加了幼虫2龄和3龄的平均龄期和死亡率，这对进一步认识与水稻互作中，二化螟发育历期的演化具有重要意义。这些发现将有助于为二化螟绿色防控及可持续治理提供新视角。