生长素调控盐胁迫下大豆根系可塑性发育的生理与分子机理

Being sessile organisms in constantly changing environment, plants have evolved various adaptive mechanisms to cope with adverse environmental stress during their life time. Our previous results have demonstrated that plant roots can remodel Root System Architecture (RSA) to prevent damage due to high salinity. The interactions between auxin and abiotic stress signal play important roles in the salt stress induced plastic development of RSA. Salt salinity is a major abiotic stress affecting soybean yield and quality. However, the study in physiological and molecular mechanisms underlying salt stress tolerance of soybean is still in its infancy. This project will analyze root response and plastic development to salt stress and the underlying physiological mechanism and the salt stress and hormonal gene regulatory interaction networks in soybean. The four specific aims of the project are to: 1) determine the physiological, morphological changes in soybean seedlings under salt stress; 2) identify the miRNAs and the target genes responsive to salt stress in the soybean roots by performing next generation deep sequencing and degradome sequencing across the soybean genome; 3) study the global gene expression patterns by carrying out cell type specific transcriptome analyses in salt stressed roots in soybean genome-wide; and 4) characterize the miRNAs and cell type specific regulatory genes closely related to auxin under salt stress. By correlating physiological and morphological responses with miRNA and gene expression profiles, the regulatory mechanisms that modulate salt response and plastic root development will be revealed. This study will provide a systematic characterization of root tissue and cell type specific regulatory networks associated with stress response and plastic development of RSA. This work lays the foundation for a broader dissection of plant responses to salt stress and understanding salt-auxin interaction during root development. The results will be especially useful in understanding salt tolerance, as well as improvement of cultivars that can tolerate salt stress in agriculture.

由于不能像动物一样躲开外界刺激，植物演化出多种多样的机制应对逆境胁迫。我们前期的研究发现根系可塑性发育是植物耐盐避害的一种重要适应机制，生长素在盐胁迫诱导的根系可塑性发育中起着关键作用。盐胁迫是影响大豆高产和稳产的重要限制因素，但对大豆的耐盐避害生理及分子调控机制几乎一无所知。本研究中，我们将主要进行以下几方面的研究：1）系统研究大豆根系对盐胁迫响应和适应的生理机理；2）利用miRNA深度测序和靶基因降解组等技术在基因组水平分离和鉴定大豆根生长和侧根发育过程中对盐胁迫响应的miRNA和靶基因；3）采用高通量单类细胞转录谱分析技术研究大豆根不同组织和细胞对盐胁迫特异响应的分子调控网络；4）选择与生长素相关的代表性miRNA和功能基因，研究大豆生长素调控盐胁迫下根系响应和可塑性发育的分子机制。通过上述研究，揭示盐胁迫下根系可塑性发育的生理机理，解析盐胁迫下调控大豆根系可塑性发育的主要信号网络。

大豆是重要的油料作物，是植物蛋白和油脂的重要来源。目前我国对国外进口依存度高达90%，培育高产和稳产大豆新品种是当务之急。根系是植物吸收水分和营养的器官，也是感受非生物逆境如盐胁迫的器官；而根瘤是大豆根系中可共生固氮的特化侧根器官，对大豆高产、稳产至关重要，且对逆境胁迫非常敏感。但大豆根系和根瘤对非生物逆境响应的分子机制研究甚少。本课题就是对大豆根系和根瘤的发育及其在盐胁迫下的可塑性发育的机制进行系统研究，重点解析非编码miRNA介导的大豆根系和根瘤发育和可塑性发育的表观遗传调控机制。在过去五年中，我们圆满完成了课题的总体研究目标，并在大豆结瘤调控机制方面取得了突破性成果。研究结果在国际有影响力的杂志Plant Cell、Plant Physiology、New Phytologist等杂志上发表论文9篇。具体进展如下：.（1）完成了大豆根系对盐胁迫的响应形态和生理学分析。（2）在基因组范围内鉴定了一批调控大豆根系及盐胁迫可塑性发育的候选miRNA（Frontier in Plant Science, 2016）。（3）明确了miR172c及其靶基因NNC1调控大豆结瘤（Plant Cell, 2014）及其根系应答盐胁迫时可塑性发育的分子机制（BMC Plant Biology，2018）。（4）通过研究miR393-GmAFB2/TIR1和miR167c-GmARF8两个分子模块及其功能，解析了miRNA通过生长素信号通路（包括生长素受体和生长素响应因子表达水平）精细调控大豆根系及根瘤发生发育的分子机制（Plant Physiology，2015；New Phytologist，2017）上。（5）获得了生长素相关的DR5::GUS的稳定转化材料，为后续深入研究生长素在大豆根系和根瘤发育和应答盐胁迫的可塑性发育过程中作用及机制提供了资源。（6）获得许多重要候选miRNA（如miR156等）和功能基因（如miRNA的靶基因和大豆生长素合成关键基因GmYUC等）的生物功能和机制也取得了阶段性进展。这些研究成果为深入解析大豆根系和根瘤发育和可塑性发育的遗传调控机制奠定了重要研究基础。此外，在项目实施中，建立和完善了相关技术和平台，为后续深入研究和科研创新提供了支撑；还培养一批年轻人才，为大豆和植物基础研究提供了后备力量。