Regulation of Shoot Development in Arabidopsis

多年来，植物中的器官再生一直令科学家们感兴趣，因为培养中再生组织的发育命运可以由两种简单的植物激素--细胞分裂素和生长素--控制。当细胞分裂素相对于生长素水平较高时，会产生新芽，而当生长素相对于细胞分裂素水平较高时，则会形成根。不定芽再生不仅是一种有趣的发育现象，而且是植物繁殖和改良的重要商业过程。了解其调控可能有助于解决芽再生效率低下的问题，而芽再生效率低下往往阻碍了改良具有商业意义的植物品种的努力。最近，本实验室利用寡核苷酸阵列(DNA芯片)分析来描述支撑芽发育过程的基因表达的全球模式。本研究分析了8000多个基因，其中数百个基因表达上调或下调，其中涉及激素信号转导和芽分生组织形成的基因。在拟南芥中，一些生态型(来自不同地理位置的菌株)在类似的组织培养条件下形成不定芽的能力不同。为了了解决定新梢发育效率的基因，人们搜索了控制再生良好的生态型(哥伦比亚)和不能再生的生态型(兰德斯堡)之间再生能力差异的基因(座位)。在第5号染色体上发现了一个主效基因，在该基因中，哥伦比亚等位基因促进了芽的形成。在第1和第4染色体上发现了另外两个较小的基因座，这些基因座上的Landsberg等位基因提高了新梢产量。这项拟议的项目将研究这些基因座如何影响新梢发育过程中的基因表达程序，以及5号染色体上的主要基因座是否控制一组特定基因的表达。利用含有20,000多个拟南芥基因的寡核苷酸阵列(DNA芯片)将被用来鉴定在新梢发育过程中受第5号染色体主基因座上的哥伦比亚等位基因或Landsberg等位基因差异调控的基因。此外，还将评估两种生态型拟南芥基因组中每个基因的表达水平，以确定是否有基因在新梢发育过程中表现出可遗传的表达模式。如果是这样的话，将对控制单个基因的基因座进行搜索，这些基因显示基因表达的可遗传变化。这种方法被称为“基因基因组学”，将寡核苷酸阵列上任何基因的表达水平视为一个度量性状，并允许人们寻找控制这些性状的基因。这是构建拟南芥新梢发育过程中基因表达因果途径的第一步。最后，我们建议在哥伦比亚生态型中鉴定位于5号染色体主基因座的提高新梢发育效率的基因(S)。这将通过一个被称为“染色体行走”的过程来完成，在这个过程中，精细的基因图谱技术被用来精确定位候选基因。

Organ regeneration in plants has intrigued scientists for years because the developmental fate of regenerating tissue in culture can be controlled by two simple plant hormones, cytokinin and auxin. At high levels of cytokinin relative to auxin, shoots are produced, while at high levels of auxin relative to cytokinin, roots are formed. Shoot regeneration is not only an interesting developmental phenomenon but also an important commercial process for the propagation and improvement of plants. Understanding its regulation may help to solve inefficiencies in shoot regeneration that often impede efforts to improve commercially significant plant varieties.Recent studies were conducted in this laboratory using oligonucleotide array (DNA chip) analysis to describe the global pattern of gene expression that underlies the shoot development process. More than 8000 genes were analyzed in this study, and several hundred were up or downregulated among them were genes involved in hormone signaling and shoot meristem formation.In Arabidopsis, some ecotypes (isolates from different geographical locations) differ in their ability to form shoots under comparable tissue culture conditions. In the effort to understand the genes that determine the efficiency of shoot development, a search was conducted for genes (loci) that control the difference in regeneration ability between one ecotype (Columbia) that regenerates well and another ecotype (Landsberg) that does not. One major locus on chromosome 5 was identified, in which the Columbia allele enhances shoot formation. Two other minor loci were identified on chromosomes 1 and 4. Landsberg alleles at these loci enhance shoot production. The proposed project will examine how these loci impact the program of gene expression during shoot development and whether the major locus on chromosome 5 controls the expression of a specific set of genes. Oligonucleotide arrays (DNA chip) with over 20,000 Arabidopsis genes will be employed to identify the genes that are differentially regulated during shoot development by the Columbia or the Landsberg alleles at the major locus on chromosome 5.In addition, the expression level of every gene in the Arabidopsis genome will be assessed in the two ecotypes to see if any genes show heritable patterns of gene expression during shoot development. If so, searches will be undertaken for loci controlling individual genes that show heritable changes in gene expression. This approach, termed "genetical genomics," treats the expression level of any gene on an oligonucleotide array as a metric trait and permits one to seek out genes that control these traits. This represents the first step in constructing causal pathways of gene expression during shoot development in Arabidopsis.Finally, it is proposed to identify the gene(s) at the major locus on chromosome 5 that enhances the efficiency of shoot development in the Columbia ecotype. This will be done by a process called "chromosome walking," in which fine-scale gene mapping techniques are used to pinpoint candidate genes.