PLANT GENE REGULATION DURING N-ASSIMILATION/FIXATION

编码谷氨酰胺独特多肽的基因 高等植物中的合成酶（GS）是一个有吸引力的系统 研究调节核基因的分子机制 参与植物特有的两个功能过程，即 叶绿体发育和固氮。 我们建议 检查编码 GS 不同形式的基因 （叶绿体和细胞质），探索分子基础 它们在叶、根和氮中的差异表达 固定豆科植物的根瘤。 本研究的具体目的 将解决以下问题：1）mRNA 是否编码 叶绿体或胞质 GS 多肽是不同的产物， 独特调控的 GS 基因，或者它们是 差异转录起始或RNA加工的产物？ 2）具体影响因素有哪些？ 叶绿体 GS mRNA 在叶子中的表达（即光、组织- 类型）？ 3）该过程涉及哪些分子机制？ 受氮感染的豆科植物根中 GS mRNA 的诱导 修复根瘤菌？ 编码不同 GS 多肽的 cDNA 克隆将是 每个 GS 特有的特征寡核苷酸探针 mRNA种类将用于检查其在体内的表达 叶（即亮/暗）、根以及根瘤发育过程中 豆类。 同源核 GS 基因将被分离， 表征并用作分子探针，以确定 围绕其调节表达的分子事件 体内。 特别是，我们将通过以下方式检查转录调控： 光、组织型或根瘤菌感染，在孤立的细胞核中 体外。 假定的反式作用转录起始因子 GS基因转录的特异性将在体外进行检查。 狂野 GS 型和启动子缺失突变体将被引入 外来植物（通过 Ti 载体）及其在 监测转基因植物对光、组织类型或 根瘤菌感染以确定所需的顺式作用 DNA 元件 用于调节基因表达。 除了定义 影响差异调节的分子机制 相关基因家族，从长远来看，这些信息可能会 应用于现有基因的修饰（即非豆科植物） 以实现与根瘤菌的成功结合。

The genes encoding the distinct polypeptides of glutamine synthetase (GS) in higher plants present an attractive system to study the molecular mechanisms which regulate nuclear genes involved in two functional processes unique to plants, namely chloroplast development and nitrogen fixation. We propose to examine the genes encoding the distinct forms of GS (chloroplastic and cytosolic), to explore the molecular basis for their differential expression in leaves, roots, and in nitrogen- fixing root nodules of legumes. The specific aims of this study will address the following questions: 1) Are the mRNAs encoding chloroplast or cytosolic GS polypeptides the products of distinct, uniquely regulated GS genes, or alternatively are they the products of differential transcript initiation or RNA processing? 2) What are the factors which contribute to the specific expression of chloroplast GS mRNA in leaves (i.e. light, tissue- type)? 3) What are the molecular mechanisms involved in the induction of GS mRNA in legume roots infected with nitrogen- fixing Rhizobia? cDNA clones encoding the distinct GS polypeptides will be characterized and oligonucleotide probes specific for each GS mRNA species will be used to examine its expression in vivo in leaves (i.e. light/dark), roots, and during nodule development in legumes. The cognate nuclear GS genes will be isolated, characterized, and used as molecular probes, to determine the molecular events which surround their regulated expression in vivo. In particular, we will examine transcriptional regulation by: light, tissue-type, or Rhizobial infection, in isolated nuclei in vitro. Putative trans-acting transcription initiation factors specific for GS gene transcription will be examined in vitro. Wild type and promoter deletion mutants of GS will be introduced into foreign plants (via Ti vectors) and their expression in the transgenic plants monitored in response to light, tissue-type, or Rhizobial infection to define cis-acting DNA elements required for regulated gene expression. In addition to defining the molecular mechanisms which effect a differential regulation of a family of related genes, in the long term, this information may b applied to the modification of existing genes (i.e. in non-legumes) to effect a successful association with Rhizobium.