title: Global transcriptome analysis of Mesorhizobium alhagi CCNWXJ12-2 under salt stress.
abstract: BACKGROUND
  Mesorhizobium alhagi CCNWXJ12-2 is a α-proteobacterium which could be able to fix nitrogen in the nodules formed with Alhagi sparsifolia in northwest of China. Desiccation and high salinity are the two major environmental problems faced by M. alhagi CCNWXJ12-2. In order to identify genes involved in salt-stress adaption, a global transcriptional analysis of M. alhagi CCNWXJ12-2 growing under salt-free and high salt conditions was carried out. The next generation sequencing technology, RNA-Seq, was used to obtain the transcription profiles.
  
  
  RESULTS
  We have compared the transcriptome of M. alhagi growing in TY medium under high salt conditions (0.4 M NaCl) with salt free conditions as a control. A total of 1,849 differentially expressed genes (fold change ≧ 2) were identified and 933 genes were downregulated while 916 genes were upregulated under high salt condition. Except for the upregulation of some genes proven to be involved in salt resistance, we found that the expression levels of protein secretion systems were changed under high salt condition and the expression levels of some heat shock proteins were reduced by salt stress. Notably, a gene encoding YadA domain-containing protein (yadA), a gene encoding trimethylamine methyltransferase (mttB) and a gene encoding formate--tetrahydrofolate ligase (fhs) were highly upregulated. Growth analysis of the three gene knockout mutants under salt stress demonstrated that yadA was involved in salt resistance while the other two were not.
  
  
  CONCLUSIONS
  To our knowledge, this is the first report about transcriptome analysis of a rhizobia using RNA-Seq to elucidate the salt resistance mechanism. Our results showed the complex mechanism of bacterial adaption to salt stress and it was a systematic work for bacteria to cope with the high salinity environmental problems. Therefore, these results could be helpful for further investigation of the bacterial salt resistance mechanism.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Liu
authors.forename: Yantao
authors.initials: Y
authors.lastname: Luo
authors.forename: Osama Abdalla
authors.initials: OA
authors.lastname: Mohamed
authors.forename: Dongying
authors.initials: D
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau,, College of Life Sciences, Northwest A&F University, Yangling 712100, Shaanxi, China. weigehong@nwsuaf.edu.cn.
authors.forename: Gehong
authors.initials: G
authors.lastname: Wei
mesh_terms: D002681:China; D007887:Fabaceae / Q000382:microbiology; D020869:Gene Expression Profiling; D059014:High-Throughput Nucleotide Sequencing; D059128:Mesorhizobium / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D009997:Osmotic Pressure; D012492:Salts / Q000378:metabolism*
chemical_list: D012492:Salts