Influence of elevated atmospheric carbon dioxide on transcriptional responses of Bradyrhizobium japonicum in the soybean rhizosphere. Bradyrhizobium japonicum

Elevated atmospheric CO2 can influence the structure and function of rhizosphere microorganisms by altering root growth and the quality and quantity of compounds released into the rhizosphere via root exudation. In these studies we investigated the transcriptional responses of Bradyrhizobium japonicum cells growing in the rhizosphere of soybean plants exposed to elevated atmospheric CO2. The results of microarray analyses indicated that atmospheric elevated CO2 concentration indirectly influences on expression of large number of Bradyrhizobium genes through soybean roots. In addition, genes involved in C1 metabolism, denitrification and FixK2-associated genes, including those involved in nitrogen fixation, microanaerobic respiration, respiratory nitrite reductase, and heme biosynthesis, were significantly up-regulated under conditions of elevated CO2 in the rhizosphere, relative to plants and bacteria grown under ambient CO2 growth conditions. The expression profile of genes involved in lipochitinoligosaccharide Nod factor biosynthesis and negative transcriptional regulators of nodulation genes, nolA and nodD2, were also influenced by plant growth under conditions of elevated CO2. Taken together, results of these studies indicate that growth of soybeans under conditions of elevated atmospheric CO2 influences gene expressions in B. japonicum in the soybean rhizosphere, resulting in changes to carbon/nitrogen metabolism, respiration, and nodulation efficiency. Overall design: Bradyrhizobium japonicum strains were grown in the soybean rhizosphere under two different CO2 concentrations. Transcriptional profiling of B. japonicum was compared between cells grown under elevated CO2 and ambient conditions. Four biological replicates of each treatment were prepared, and four microarray slides were used for each strain.

大气CO₂浓度升高可通过改变根系生长以及经根系分泌作用释放到根际的化合物的质量与数量，影响根际微生物的群落结构与功能。本研究探究了生长于大气CO₂浓度升高的大豆根际的大豆慢生根瘤菌（Bradyrhizobium japonicum）细胞的转录响应。微阵列（microarray）分析结果显示，大气CO₂浓度升高可通过大豆根系间接影响大量大豆慢生根瘤菌基因的表达。此外，相较于在大气CO₂浓度正常的生长环境下培育的植株与菌株，根际CO₂浓度升高条件下，参与一碳（C1）代谢、反硝化作用及FixK₂相关基因（包括固氮、微厌氧呼吸、呼吸型亚硝酸还原酶及血红素生物合成相关基因）的表达量均显著上调。参与脂壳寡糖结瘤因子（Nod factor）生物合成以及结瘤基因负转录调控因子nolA与nodD2的基因表达谱，同样受CO₂浓度升高条件下生长的植株影响。综上，本研究结果表明，大气CO₂浓度升高环境下生长的大豆，会影响大豆根际内大豆慢生根瘤菌的基因表达，进而改变其碳/氮代谢、呼吸作用及结瘤效率。实验设计：将大豆慢生根瘤菌菌株置于两种不同CO₂浓度的大豆根际环境中培养，对比分析CO₂浓度升高与正常环境下生长的菌株细胞的转录谱。每个处理设置4个生物学重复，每个菌株使用4张微阵列芯片完成检测。