miR172c/NNC1模块调控大豆共生固氮和生长发育分子机理研究

Symbiotic nitrogen fixation (SNF) is a fundamental scientific question in biology. The SNF efficiency is critical for plant growth, yield and seed quality in legumes. Under low nitrogen, plants release flavonoids to induce production of Nod factors in rhizobia, which in turn activate nodulation signaling cascades through recognition by Nod factor receptors (NFRs). As a result, root nodules form to fix N2 to NH4+, which can promote plant growth and development. Previously, we identified a key molecular module miR172c/NNC1 that regulates rhizobia infection, nodule formation and nitrogen fixation of mature nodules; recently we found that the module also mediates nitrogen sensing, nitrogen assimilation, and plant growth and flowering. We hypothized that miR172c/NNC1 may act as nod to integrate various signaling pathways through NNC1 target genes. However, the molecular mechanism underlying miR172c/NNC1-mediated regulatory network that control a variety of biological processes during nodulation remain is unclear. In this study, we will 1) adopt the combinatorial approach including ChIP-seq and RNA-seq to identify the target genes of NNC1 during nodulation; 2) use yeast two hybrid assay to find the NNC1-interacting proteins; 3) search the natural variations of miR172c/NNC1 that confer enhanced SNF efficiency; 4) functionally investigate the selected key genes or proteins. The goal is to elucidate the molecular regulatory network that precisely modulates nitrogen sensing, rhizobia infection, nodule organogenesis, nitrogen fixation, nitrogen assimilation and plant growth & development in soybean. The findings will facilitate further understanding of SNF and the link between SNF and plant development in legumes.

大豆共生固氮的遗传机理不仅是最基本的生物学问题, 也是关乎其产量和品质重要问题。在氮匮缺时，植物诱导根瘤菌产生结瘤因子（NF），在其被植物结瘤因子受体识别后激发信号级联完成根瘤菌侵染、结瘤、固氮和调控植物发育过程。前期我们发现miR172c/NNC1分子模块在大豆结瘤和根瘤数量调控中发挥核心作用，还发现它们参与植物对低氮响应、根瘤菌侵染、根瘤固氮和植物发育, 但miR172c/NNC1模块调控这些生物过程的分子机制还不清楚。在本研究中，我们将：1）利用ChIP-seq和转录组分析鉴定NNC1的靶基因；2）用酵母双杂和免疫共沉淀-质谱法筛选NNC1的互作蛋白；3）挖掘miR172c/NNC1优异等位变异；4）选择代表性NNC1靶基因和互作蛋白，研究其功能及作用机制。研究结果将解析miR172c/NNC1调控大豆共生固氮及植物发育的分子网路，为培育高固氮效率大豆提供科学依据。

大豆共生固氮是关乎其产量和品质重要问题。在氮匮缺时，植物诱导根瘤菌产生结瘤因子（NF），在其被植物结瘤因子受体识别后激发信号级联完成根瘤菌侵染、结瘤、固氮和调控植物发育过程。前期我们发现miR172c/NNC1分子模块是参与植物对根瘤菌侵染、结瘤与根瘤固氮及植物生长发育的关键因子, 但miR172c/NNC1模块调控这些生物过程的分子机制还不清楚。在本研究中，我们首次证明了，共生信号和根瘤固定的氮素协同调控植物开花并解析了背后的机制。发现根瘤菌诱导的miR172c作为可移动的共生信号通过长距离运输叶片，与氮素在叶片中诱导的miR172c及发育开花途径诱导的miR172汇合，通过抑制其靶基因GmTOE4a激活开花素基因GmFT2a/5a，从而促进开花；第二，阐明了miR172c/NNC1模块受GmNINa调控并耦合NF和AON信号通路调控根瘤数量的机制；第三，解析了AON通过细胞分裂素降低结瘤的新机制。发现AON诱导B型响应因子GmRR11d直接抑制GmNIN1a并与结瘤信号通路关键转录因子GmNSP1a互作抑制其对GmNIN1a转录激活作用，从而降低NF活性并提高根对细胞分裂素的敏感性从而实现抑制结瘤；第四，解析了蓝光抑制结瘤的新机制。发现短时间蓝光通过其受体GmCRY1s激活地下结瘤抑制因子STF1/2，进而抑制 GmNIN1a表达及结瘤；此外，还发现其他调控大豆结瘤的关键调控因子，如miR156b/ GmSPL9模块和转录因子GmNAC181分别通过抑制与激活GmNIN1a调控大豆结瘤，发现油菜素内酯和脱落酸负调控大豆结瘤的分子机制。上述研究结果系统解析了大豆共生固氮及其调控植物发育的分子网路，为培育高固氮效率大豆提供科学依据。