Control of Hormogonium Differentiation in the Symbiotic Cyanobacterium Nostoc Punctiforme

固氮蓝藻Nostoc punctiformme是丝状蓝藻（蓝绿藻）的典型代表，它的营养细胞有四种发育选择，是所有细菌中最复杂的。根据环境条件的不同，营养细胞可以：生长和分裂，继续营养生长周期，短暂分化为活动细丝，称为激殖细胞，短暂分化为静止细胞，称为无动子细胞，或最终分化为异囊，即固氮位点。本项目的重点是确定参与珠原体分化和行为的调节机制。活动的绒原菌丝在新栖息地的殖民中起作用，并作为感染单位与植物和真菌建立共生关系。蓝藻是其他生物维持稳态环境条件的重要的还原碳和氮的生产者。例如，在与地衣的共生关系中，固氮蓝藻有助于在贫瘠的土壤中消耗大气中的二氧化碳，减轻全球变暖的程度。这个项目有两个总体目标。1. 确定滴虫分化过程中差异基因表达的程度，利用二维蛋白凝胶电泳鉴定差异合成蛋白，确定所选蛋白的氨基酸序列，并利用点状氮虫基因组数据库鉴定编码该蛋白的相应基因。2. 一组基因的特征，这些基因合成的蛋白质可能在一种代谢化合物的产生中起作用，这种代谢化合物抑制了原殖菌的分化。具体的重点将放在假设的转录抑制基因的活性上。本研究结果对解决发育生物学中调控途径的层次、整合和进化问题具有重要价值

0080805MeeksThe nitrogen-fixing cyanobacterium Nostoc punctiforme exemplifies filamentous cyanobacteria (blue-green algae) whose vegetative cells have four developmental alternatives and are the most complex of all bacteria. Depending on the environmental conditions vegetative cells can: grow and divide to continue the vegetative growth cycle, transiently differentiate into motile filaments called hormogonia, transiently differentiate into resting cells called akinetes, or terminally differentiate into heterocysts, the sites of nitrogen fixation. This project focuses on identifying the regulatory mechanisms involved in hormogonium differentiation and behavior. Motile hormogonium filaments serve in the colonization of new habitats and as the infective units in establishment of symbiotic associations with plants and fungi by the Nostoc. Cyanobacteria are important producers of reduced carbon and nitrogen for other organisms in maintaining steady state environmental conditions. In symbiotic associations with lichens for example, nitrogen-fixing cyanobacteria contribute to the consumption of atmospheric carbon dioxide in poor soils and lessen the extent of global warming. This project has two overall objectives. 1. Determine the extent of differential gene expression during hormogonium differentiation, using two dimensional protein gel electrophoresis to identify differentially synthesized proteins, determine the amino acid sequence of selected proteins and use the N. punctiforme genome data base to identify the corresponding genes that encode the proteins. 2. Characterization of a set of genes, whose synthesized proteins may function in the production of a metabolic compound that represses hormogonium differentiation. Specific focus will be on the activity of the hypothetical transcriptional repressor of the genes. The results of this study will be of value in addressing questions of the hierarchy, integration and evolution of regulatory pathways in developmental biology using