Bacteroid development in rhizobia

大气氮的生物固定是全球氮循环的重要组成部分，对全球农业特别有价值。在全球范围内，根瘤菌和豆类之间的固氮共生是农业系统氮输入的主要来源，许多豆类物种，如豌豆、扁豆、大豆和鹰嘴豆是重要的粮食作物。根瘤菌与豆科植物的相互作用已经得到了广泛的研究，但这个过程是复杂的，需要进一步的基础研究来充分认识这种复杂性。根瘤菌诱导豆科植物形成根瘤，在这些根瘤中，细菌将大气中的氮转化为植物可以利用的形式。当根瘤菌分化为共生细胞（类细菌）时发生的戏剧性转变已被最近的微阵列基因表达和蛋白质组学研究清楚地记录下来。然而，调节类细菌分化的机制，特别是在结瘤过程中基因表达的下调，在很大程度上是未知的。我的研究计划的长期目标是使用基于遗传学的方法来发现控制根瘤菌中类细菌发育的未知调控途径，并确定类细菌发育所需的新基因。更具体地说，拟议的研究将确定在类细菌发育过程中控制细胞分裂、运动和外膜蛋白相关基因下调的调节因子和信号。蛋白酶作为类细菌发育的调节剂的作用也将在本提案中进行研究。这项研究的结果可能应用于其他细菌-宿主关系，特别是α -变形杆菌类中的致病相互作用，可能用于确定调节致病过程的新机制。

The biological fixation of atmospheric nitrogen is a critical component to the global nitrogen cycle and is particularly valuable to worldwide agriculture. Globally, nitrogen fixation symbioses between rhizobia and legumes are the major source of nitrogen input to agricultural systems, and many legume species, such as peas, lentils, soybeans and chickpeas are important food crops. Rhizobial-legume interactions have been studied extensively, but the process is complex and further fundamental research is required to appreciate this complexity fully. Rhizobia induce the formation of root nodules on legume plants, and within these nodules, the bacteria convert atmospheric nitrogen to a form that is useable by the plants.  The dramatic transformation that occurs when rhizobia differentiate into symbiont cells (bacteroids) has been clearly documented by recent microarray gene expression and proteomic studies. However, the mechanisms that regulate bacteroid differentiation, particularly the down-regulation of gene expression during nodulation, are largely unknown. The long-term objectives of my research program are to use genetics based methodologies to discover unknown regulatory pathways that control bacteroid development in rhizobia and to identify novel genes required for bacteroid development. More specifically, the proposed research will identify regulators and signals that control the down-regulation of genes related to cellular division, motility and outer membrane proteins during bacteroid development. The role of proteases as regulators of bacteroid development will also be studied in this proposal. Results from this research may be applied to other bacterial-host relationships, particularly pathogenic interactions within the alpha-proteobacteria class, possibly to identify novel mechanisms that regulate the pathogenic process.