2009-01-012024-05-17https://scholars.lib.ntu.edu.tw/handle/123456789/684026摘要：Sesbania rostrata （中文名：長喙田菁）是一種熱帶豆科植物，不僅根毛可產生根瘤， 若是將其共生根瘤菌 Azorhizobium caulinodans 接種在側根（莖）上也可長出具固氮功能的莖瘤。 S. rostrata -A. caulinodans 共生系統具有以下優點，利於做為研究根瘤成熟機制的材料: 不同於一般的根瘤菌藉由Root Hair deformation and curing 的方式從根毛進入到植物組織， A. caulinodans 可從 S. rostrata 莖上的各個不定根原基（adventitious root primodia ）突起處藉由Crack entry 的方式直接進入到植物體內形成莖瘤，也因此接種位置會與形成莖瘤的地方一致。 此外，由於是以Crack entry的方式感染，接種的同時亦啟動一連串的結瘤程序，因此只要是同時間接種的各株植物體皆可視為同步進行結瘤，利於做時序性的成熟過程追蹤。 我們已在先前的研究中藉由大規模的 in vivo 篩選作業獲得多數與根瘤成熟相關的 A.caulinodans Tn5 突變株。本研究計畫以 ORS571-Ao3-F05 這一個突變株做為實驗對象。 根據Ao3-F05突變株的Tn5周邊序列，以及與A. caulinodans ORS571的基因體核酸序列比較分析的結果，Tn5轉座子插入在染色體分配系統的parA蛋白基因上。 接種ORS571-Ao3 -F05所生成的 S. rostrata 莖瘤無論是大小或是固氮能力均劣於同時期接種的野生型莖瘤。 將Ao3- F05莖瘤做水平方向切面會發現到同一株植物體上分別存在有不等比例的綠色，淡紅色與白色這3種莖瘤。 綠色代表初期莖瘤尚未開始進行固氮反應， 淡紅色顯示莖瘤已具有固氮能力，白色則是表示莖瘤已經在老化階段 。這結果說明被Ao3-F05突變株所感染的植物體所生成的莖瘤會停滯在不同的生長階段。 根瘤的成熟、根瘤的維持到表達共生固氮的這一段過程的分子機制至今仍然不明。 本研究將藉由分子生物學、生物化學、細胞生物學、基因體學、蛋白質體學等分析方法探討根瘤菌的染色體分配基因（parA）如何調控根瘤成熟時機。盼能瞭解根瘤菌與宿主植物在根瘤成熟階段中的分子訊息傳導途徑。我們更希望這個研究的發現成為將來應用在穀物作物的共生固氮上之重要基礎。 <br> Abstract: Sesbania rostrata, which is a tropical legume, forms N2-fixing nodules on the stem as well as on the roots in symbiosis with Azorhizobium caulinodans. Stem-nodules occur at the site of adventitious root primordial via crack entry, while root-nodules are formed at the curled root hair. Because stem-nodules are formed at the predetermined nodulation sites and develop synchronously, it is easy to observe the stem-nodules through time. Taken together, stem-nodules can be useful for analysis of nodule-formation mechanism. In a previous study, we have identified many novel genes which are involved in the developmental process of nodulation through a large scale in vivo screen for Tn5-inserted mutants of A.caulinodans ORS57. We found that a mutant (named ORS571-Ao3-F05) which was defective in a chromosome partition gene (parA), resulted in immature stem-nodules on S. rostrata. The Ao3-F05 stem-nodules were relatively smaller and the nitrogen fixation ability was worse than those induced by wild-type. Three kinds of stem-nodules (green, pale-red and white in the central tissue) were generated in indefinite proportion on each plant. Green stands for young nodule, pale-red means the nodule has the ability to fix nitrogen, and white indicates the nodule has already been senesced. It suggests that the development of those aberrant stem-nodules was halted in diverse maturity stage. To date, the genes and factors which are involved in nodule maturation process, and which regulate it, have not been well identified. In this study, we will use a combination of molecular, biochemical, cell biology, genetic and proteomic approaches to elucidate the role of parA gene in maturation of nodules. We also expect to understand how host legume plants perceive specific signals from rhizobia, and how they transduce symbiotic signals to downstream components. We hope the findings of this study will serve as a foundation for conferring symbiotic nitrogen fixation to non-legume plants.根瘤菌豆科植物共生固氮染色體分配基因rhizobiumlegumesymbiotic nitrogen fixationchromosome partition gene