Amplifying and Fine-Tuning Rsm sRNAs Expression and Stability to Optimize the Survival of in Nutrient-Poor Environments.

In the beneficial plant root-associated strain NFM421, the GacS/GacA two-component system positively controls biofilm formation and the production of secondary metabolites through the synthesis of , and . Here, we evidenced the genetic amplification of Rsm sRNAs by the discovery of a novel 110-nt long sRNA encoding gene, , generated by the duplication of (formerly ). Like the others genes, its overexpression overrides the mutation. We explored the expression and the stability of , , and encoding genes under rich or nutrient-poor conditions, and showed that their amount is fine-tuned at the transcriptional and more interestingly at the post-transcriptional level. Unlike and , we noticed that the expression of and genes was exclusively GacA-dependent. The highest expression level and longest half-life for each sRNA were correlated with the highest ppGpp and cyclic-di-GMP levels and were recorded under nutrient-poor conditions. Together, these data support the view that the Rsm system in is likely linked to the stringent response, and seems to be required for bacterial adaptation to nutritional stress.