MtRGF3肽调节蒺藜苜蓿固氮根瘤发育的分子机制

Leguminous plants interacting with rhizobia form nitrogen-fixing nodules to provide a nitrogen source, which is of great significance in sustainable agricultural development and ecological environment protection. The nitrogen-fixing nodule development of legumes such as Medicago truncatula is regulated by a variety of peptide hormones. RGF is a novel class of peptide hormones that regulate root development discovered in Arabidopsis recently. Our previous studies showed that the MtRGF3 peptide and its coding gene negatively regulate nitrogen-fixing nodule formation in M. truncatula. The mechanism of the MtRGF3 peptide is mediated by receptor-mediated signaling pathways to modulate Nod factor or immune signal transduction for regulating nitrogen-fixing nodule development. To test this hypothesis, we intend to use genetics, biochemistry, and cell biology techniques to identify receptor kinase molecules recognizing the MtRGF3 peptide and their interacting proteins, and to determine their functions in Nod factor or immune signaling. The implementation of this project has important theoretical significance for deep understanding of the molecular mechanism of RGF peptides and the regulatory mechanism of nitrogen-fixing root nodule development in legumes, and provides theoretical basis for the engineering application of symbiotic nitrogen fixation principles.

豆科植物受根瘤菌诱导形成固氮根瘤，在可持续农业发展和生态环境保护方面具有重要意义。根瘤发育受多种肽类激素调节，RGF是近年来在拟南芥中发现的一类调节根系发育的新型肽类激素。我们前期的研究显示MtRGF3肽及其编码基因负调节蒺藜苜蓿固氮根瘤的形成，其作用机制可能是通过受体介导的信号途径，调节下游结瘤因子或者免疫信号途径，从而影响固氮根瘤的形成。为了验证这一假设，我们拟应用遗传学、生物化学和细胞生物学技术，鉴定识别MtRGF3肽的受体激酶分子及其互作蛋白，确定其在结瘤因子或者免疫信号传导过程中的作用，从而揭示MtRGF3肽调节根瘤发育的分子机理。本项目的实施，对于深入理解肽类激素RGF的作用机理和豆科植物固氮根瘤发育的调控机制具有重要理论意义，为共生固氮原理的工程化应用提供理论依据。

根生长因子RGF是一类受磺酸化修饰的小肽分子，在植物生长发育及抗病反应中发挥重要的调控作用。通过本项目的实施，我们在豆科模式植物蒺藜苜蓿中鉴定到一个RGF成员—MtRGF3。研究表明MtRGF3基因表达受根瘤菌诱导，且在根瘤发育的各个阶段均有表达。本项目创制了苜蓿MtRGF3的过表达及RNAi敲减发根遗传转化材料，结合肽处理实验详细解析了MtRGF3小肽在苜蓿根瘤发育中的功能。同时，通过RNA-seq及qRT-PCR实验解析了MtRGF3负调控苜蓿根瘤形成的机制。此外，本项目还鉴定到了苜蓿七个RGF可能的受体MtRGFR1-7，并从遗传学及生理学等角度对受体基因逐个做了功能研究，发现MtRGFR2、MtRGFR4及MtRGFR6作为受体介导RGF3调控豆科植物根瘤形成。本研究的价值：1）深入解析了MtRGF3调控豆科植物根瘤形成的分子机制，2）为豆科作物高产育种提供了新的基因资源。