Laranjo Marta, Alexandre Ana, Oliveira Solange
ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Universidade de Évora, Pólo da Mitra, Ap. 94, 7002-554, Évora, Portugal.
Appl Microbiol Biotechnol. 2014 Aug;98(16):7137-47. doi: 10.1007/s00253-014-5875-4. Epub 2014 Jun 17.
Rhizobia are legume bacterial symbionts that fix nitrogen in the root nodules of plants. The aim of the present study was to investigate the global transcriptional response of rhizobia upon an acidic shock. Changes in the transcriptome of cells of Mesorhizobium loti strain MAFF303099 upon an acidic shock at pH 3 for 30 min were analysed. From a total of 7,231 protein-coding genes, 433 were found to be differentially expressed upon acidic shock, of which 322 were overexpressed. Although most of the overexpressed genes encode hypothetical proteins, the two most represented Cluster of Orthologous Group (COG) categories are 'defence mechanisms' and 'transcription'. Differentially expressed genes are dispersed throughout the chromosome, with the exception of the symbiosis island, where most genes remain unchanged. A significant number of transcriptional regulators and ABC transporter genes are overexpressed. No overexpression of genes typically associated to acid tolerance in rhizobia, such as act and exo genes, was detected. Overall, this study suggests a transcriptional response to acidic shock of M. loti distinct from other rhizobia. Additional studies are in course to explore the role of some of the highly overexpressed genes and to further elucidate the molecular bases of acid stress response.
根瘤菌是豆科植物的细菌共生体，可在植物根瘤中固氮。本研究的目的是调查根瘤菌在酸性冲击后的全局转录反应。分析了中慢生根瘤菌MAFF303099菌株细胞在pH 3酸性冲击30分钟后的转录组变化。在总共7231个蛋白质编码基因中，发现433个基因在酸性冲击后差异表达，其中322个基因过度表达。虽然大多数过度表达的基因编码假定蛋白，但最具代表性的两个直系同源簇（COG）类别是“防御机制”和“转录”。差异表达基因分散在整个染色体上，但共生岛除外，该区域大多数基因保持不变。大量转录调节因子和ABC转运蛋白基因过度表达。未检测到根瘤菌中通常与耐酸性相关的基因（如act和exo基因）的过度表达。总体而言，本研究表明中慢生根瘤菌对酸性冲击的转录反应与其他根瘤菌不同。正在进行进一步研究以探索一些高度过度表达基因的作用，并进一步阐明酸胁迫反应的分子基础。
