Table_3_The Sinorhizobium meliloti Nitrogen Stress Response Changes Radically in the Face of Concurrent Phosphate Stress.XLSX

Expression of hundreds of S. meliloti genes changed more than two-fold in response to either nitrogen or phosphate limitation. When these two stresses were applied together, stress responsive gene expression shifted dramatically. In particular, the nitrogen stress response in the presence of phosphate stress had only 30 of about 350 genes in common with the 280 genes that responded to nitrogen stress with adequate phosphate. Expression of sRNAs was also altered in response to these stresses. 82% of genes that responded to nitrogen stress also responded to phosphate stress, including 20 sRNAs. A subset of these sRNAs is known to be chaperoned by the RNA binding protein, Hfq. Hfq had previously been shown to influence about a third of the genes that responded to both nitrogen and phosphate stresses. Phosphate limitation influenced changes in gene expression more than nitrogen limitation and, when both stresses were present, phosphate stress sometimes reversed the direction of some of the changes induced by nitrogen stress. These nutrient stress responses are therefore context dependent.

苜蓿中华根瘤菌（S. meliloti）的数百个基因在遭受氮限制或磷限制胁迫时，其表达量发生2倍以上的变化。当两种胁迫同时施加时，胁迫响应基因的表达谱发生显著改变。具体而言，当存在磷胁迫时响应氮胁迫的约350个基因中，仅有30个与磷充足条件下响应氮胁迫的280个基因存在交集。小RNA（sRNAs）的表达同样会响应上述营养胁迫而发生改变。响应氮胁迫的基因中有82%同时也响应磷胁迫，其中包含20个sRNAs。已有研究证实，此类sRNAs中的一部分可由RNA结合蛋白Hfq（Hfq）充当分子伴侣发挥调控功能。此前已有研究表明，Hfq可调控约三分之一同时响应氮胁迫与磷胁迫的基因。磷限制对基因表达的调控效应强于氮限制；当两种胁迫同时存在时，磷胁迫有时会逆转部分氮胁迫诱导的基因表达变化方向。由此可见，这类营养胁迫响应具有环境依赖性。