The existence of multiple adenylate cy- clase encoding genes implies the importance of cAMP in Sinorhizobium meliloti 1021. In this study, as a pioneer step of understanding cAMP roles, mi- croarray analysis on S. meliloti was carried out for the function of exogenous cAMP. To our surprise, the result showed that the transcriptions of glnII and glnK genes were significantly upshifted in the presence of exogenous cAMP in S. meliloti. This phenomenon is further confirmed in S. meliloti that the expression of either glnII or glnK promoter-lacZ translational fusion is higher in the presence of exogenous cAMP. Therefore, for the first time, we have identified genes from S. meliloti whose expression is activated by cAMP. The potential physiological role of upregula- tion of glnII and glnK by cAMP is discussed.
Gene expression profiles of a Si- norhizobium meliloti 1021 nifA mutant and wild type nodule bacteria were compared using whole genome microarrays. The results revealed a large scale al- teration of gene expression (601 genes) in the nifA minus background. The loss of NifA altered the ex- pression of many functional groups of genes (mac- romolecular metabolism, TCA cycle and respiration, nodulation and nitrogen fixation) and may lead to quite different life stages of the nodule bacteria. Upregulation of fixK and its associated genes was observed in the nifA mutant nodule bacteria. Addi- tional quantitative real-time PCR experiments re- vealed that the transcript levels of fixLJ were signifi- cantly upshifted in the nifA mutant nodule bacteria. Putative NifA binding sites were predicted by a statis- tical method in the upstream sequences of 13 differ- entially regulated genes from the nifA- transcriptome.
