Bacteroid development in rhizobia

大气氮的生物固定是全球氮循环的关键组成部分，对全球农业特别有价值。在全球范围内，根瘤菌和豆科植物之间的固氮共生是农业系统氮素输入的主要来源，许多豆科植物，如豌豆、小扁豆、大豆和鹰嘴豆是重要的粮食作物。根瘤菌-豆科植物的相互作用已被广泛研究，但其过程是复杂的，需要进一步的基础研究才能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，细菌将大气中的氮素转化为植物可利用的形式。最近的微阵列基因表达和蛋白质组研究清楚地证明了根瘤菌分化为共生细胞(类杆菌)时发生的戏剧性转变。然而，调控类菌分化的机制，特别是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菌生长的未知调控途径，并识别类菌生长所需的新基因。更具体地说，这项拟议的研究将确定在类细菌发育过程中控制与细胞分裂、运动和外膜蛋白相关的基因下调的调节器和信号。在这项提案中，还将研究蛋白水解酶作为类菌体发育调节因子的作用。这项研究的结果可能应用于其他细菌-宿主关系，特别是α-蛋白细菌类内的致病相互作用，可能用于识别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.