S. meliloti 1021 WT and ΔcspA2 ΔcspA4 whole transcriptome sequencing from free-living and symbiotic nodules. Sinorhizobium meliloti

Rhizobia are soil bacteria that can associate with some legumes and participate in symbiotic nitrogen fixation. Bacterial CspA family members are small, single stranded nucleic acid binding proteins. Differentiation of rhizobial bacteria from a free-living to symbiotic state within legume root nodules follows a massive re-programming of bacterial gene expression. Here, the role of Sinorhizobium meliloti CspA family members in symbiotic development with Medicago sativa (alfalfa) was investigated. We defined expression patterns of CspA family members, identified CspA interacting RNAs, and investigated phenotypes and transcriptional defects associated with cspA deletion strains. We propose that these proteins affect rhizobial physiology through their global control of the cellular RNA secondary structure strength environment and through specific modulation of small non-coding RNA (sRNA) structures involved in cis-regulation of stress responsive sigma factor expression. This work describes an RNA structure mediated mechanism important for bacterial stress adaptation and symbiotic development within a plant host. Overall design: Illumina sequencing was performed with isolated total RNA from exponential phase free-living culture and symbiotic nodule tissue 28 dpi