超过80%的陆地植物都能与丛枝真菌形成共生——丛枝菌根（AM），这种共生关系的建立依赖于一套起源古老并在不同植物类群中保守的植物共生基因。但是，植物如何调控共生基因表达，以维持和谐的共生关系？以及这种调控作用是如何演化的？目前尚不清楚。本项目拟在前期发现植物miRNA对AM共生调节的基础上，以被子植物不同演化分支的两个代表性物种（双子叶植物番茄和单子叶植物水稻）为切入点，结合高通量测序和生物信息学分析，比较两种植物共生响应miRNA的谱系组成，发现物种间保守的调节AM共生的植物miRNA，鉴定其靶基因，并通过转基因、基因敲除等技术对这些miRNA进行功能验证，探讨其调节AM共生的分子机制。最后，通过调查番茄和水稻间保守的共生响应miRNA在陆地植物关键演化节点的存在状况和调控特性，追溯植物miRNA对AM共生调节作用的起源及演化，从表达调控的全新角度揭示植物AM共生建立的分子和演化机制。

Arbuscular mycorrhiza (AM) is an ancient symbiosis that originated over 400 million years ago and widespread in over 80% of land plant species from all major land-plant lineages, including hornworts, liverworts, lycopods, ferns, and angiosperms. The formation of AM with arbuscular mycorrhizal fungi (AMF) would assist plants in the assimilation of water and nutrients from the soil, which may have played a key role in facilitating plant colonization of the terrestrial environment. Establishment of an efficient symbiosis relies on a set of highly conserved 'symbiotic genes' characterized mainly in legumes. These symbiotic genes are required for the perception of AMF signals, root colonization, arbuscule development and to control the level of root colonization. Loss of symbiotic genes often results in defective in formation of AM symbiosis. Currently, how plants have evolved to tune the expression of symbiotic genes so that they are not over-colonized by AMF but maintain an efficient symbiosis relationship are still poorly understood. Recently, the identification of several miRNAs involving in AM symbiosis opened a new era for studying the regulation of AM symbiosis at transcription level. To obtain further insights into the role of miRNAs in AM symbiosis, this project planned to investigate the molecular mechanism and evolutionary pattern of AM symbiosis-regulating miRNAs from the following aspects. Firstly, a global survey of AM-responsive miRNAs in representative species from two deep-diverged angiosperm lineages of dicot (tomato) and monocot (rice) will be performed by high-throughput sequencing and bioinformatics analysis, through which the conserved and species-specific AM-responsive miRNAs could be distinguished and the shaping forces could be traced. Secondly, the interaction of a set of conserved AM-responsive miRNAs and their predicted target genes will be tested and their exact functions in AM symbiosis will be determined. Finally, the origin and evolution of these conserved AM symbiosis-regulating miRNAs and target genes will be explored by searching their homologs from key land plant lineages. The progress made by this project would enhance our understanding on how miRNAs were recruited by plants to fine tune an anciently originated symbiotic relationship and provide new insights into the molecular mechanism and evolutionary pattern of AM symbiosis.