桡足类是海洋生态系统中次级生产者的重要组成部分，在海洋食物网中起着承上启下的作用。桡足类共生原生生物与其种群动态密切相关，对海洋生态系统的多样性、能量传递及物质循环产生影响。研究桡足类共生原生生物的多样性与共生机制对揭示海洋生物共生策略及其对海洋生态系统结构和功能的调控作用具有重要意义。但由于其个体小、生活史复杂，分离及形态鉴定难度大，制约了在多水平上研究其多样性及功能。本项目组成功开发出了特异性地抑制桡足类rDNA扩增及分离桡足类mRNA的方法，大大提高了桡足类共生原生生物DNA及RNA捕获效率。本项目拟以西北太平洋桡足类优势种及其共生原生生物为研究对象，利用宏DNA条形码技术，研究桡足类共生原生生物的多样性、分布特征及动态变化；在构建原位基因表达谱基础上，分析共生关系发生及维持的分子调控机制，阐释共生原生生物与桡足类种群动态变化的关系，为研究海洋微型生物共生策略及其生态功能奠定基础。

Copepods as the most numerous secondary producer in the marine ecosystem, link the phytoplankton and higher trophic levels in marine food web. The protistan symbionts in copepods are involved in regulating population dynamics of copepods, consequently impacting the diversity, energy transfer and material cycling of marine ecosystem. To study the diversity and symbiotic mechanism of protistan symbionts in copepods is critical to understand the ecological roles of the symbiosis in regulating the structure and function of marine ecosystem. However, due to the small size and complex life cycle, isolation and morphological identification of the protistan symbionts from copepod are difficult. In previous studies, we developed the protocols to PCR-amplify 18S rDNA from the eukaryotes other than copepods, and separate copepod-specific mRNA from those of other eukaryotes. These protocols enhance the efficiency in capturing the DNA and RNA of protistan symbionts in copepods. In the proposed study, we will investigate diversity, distribution and dynamics of protistan symbionts in the dominant copepods of Northwest Pacific using metabarcoding techniques; analyze the molecular mechanism regulating initiation and maintenance of symbiosis using in situ gene expression profiling (metatranscriptome). The outcome of this project will shed light on the relationship of protistan symbionts and the population dynamics of copepods, also lay a foundation for the further studies on the symbiotic strategies and ecological roles of marine microbial symbionts.