## 1 Introduction  
The RNA-binding protein CsrA (carbon storage regulator) and its homolog RsmA (regulator of secondary metabolites) regulate a variety of genes at the post-transcriptional level. Their regulatory activity is modulated by regulatory small RNA (sRNA) antagonists of CsrA/RsmA. Functional homologs of the Csr/Rsm system have been discovered in many Gram-negative genera, including _Escherichia_[1], _Salmonella_[2], _Vibrio_[3], _Legionella_[4], _Yersinia_[5] and _Pseudomonas_[6, 7, 8], as well as in some Gram-positive bacteria such as the _Bacillus_ genus [9].  
The wide distribution of the Csr/Rsm regulatory system in Eubacteria, including animal/plant pathogenic species as well as plant growth-promoting rhizobacteria (PGPR), illustrates that this well-conserved system is involved in various essential functions [10, 11]. Indeed, small RNAs positively controlled by either the BarA/UvrY or GacS/GacA two-component systems have been shown to regulate various functions by coordinating the expression of a set of target genes post-transcriptionally [12, 13]  
The number and size of sRNAs involved in this system are variable. In _Escherichia coli_, the protein repressor CsrA is regulated by two sRNAs, CsrB and CsrC. These sRNAssequester CsrA by mimicking its recognition sequence [14; 15]. Here, CsrB sRNA, a 360-nucleotide long RNA, works in concert with CsrC sRNA (250 pts). Two homologs were found in _Pseudomonas aeruginosa_ and named RsmY (124 nt) and RsmZ (115 nt) [7]. A third Rsm sRNA, RsmX (119 nt), was discovered in _Pseudomonas protegens_ (formerly _Pseudomonas fluorescens_) CHA0 [6] and predicted to be found in other species including _P. fluorescens_ Pf-5, _P. fluorescens_ Pf0-1, _Pseudomonas putida_ KT2440 and _Pseudomonas syringae_ pv. tomato DC3000. Surprisingly, up to five RsmX encoding genes have been described in _P. syringae_[8]. Moreover, experiments with artificial RsmY-like sRNAs have demonstrated that conservation of size and/or primary sequence is not essential for Rsm functions [16]. In fact, the regulatory mechanism is linked to appropriate exposure of mimicked CsrA/RsmA recognition motif.  
In general, Csr and Rsm sRNAs seem to be redundant [7; 17; 18]. However, although all Rsm sRNAs are positively controlled by GacA, additional regulators have been identified, such as PsrA, which activates _rsmZ_ in _P. protegens_ CHA0 [19] and HptB, which exclusively controls _rsmY_ in _P. aeruginosa_[20]. These additional regulators certainly enable a fine-tuning control by integrating various signals.  
We have previously, shown that spontaneous mutations in either _gacS_ or _gacA_ in _P. brassicacarum_ can alter many phenotypes typically associated with phytobeneficial traits, as well as root colonization and modification of the root architecture [18; 21; 22; 23]. These traits include secretion of exoenzymes such as protease and lipase [24], production of antifungal metabolites (DAPG and cyanide) and \(N\)-acyl-homoserine lactones, the phytohormone auxin, biofilm formation, alginate production, chemotaxis, and type VI secretion [18]. In addition, overexpression of either _rsmX_, _rsmY_, or _rsmZ_ fully suppressed the pleiotropic _gacA_ or _gacS_ mutations and restored the WT phenotypes in _P. brassicacarum_ variants [18].  
The primary goal of this study was to determine whether _P. brassicacarum_ genome encodes other Rsm sRNAs and whether their overexpression could override the _gacA_ or _gacS_ mutation. The second part of our work aimed at evaluating the expression and stability of Rsm sRNAs under conditions of different nutrient levels. Finally, to establish the reliability of the results, the analysis of metabolites involved in stringency and biofilm formation was carried out.