## 5 Conclusions  
The amplification of Rsm sRNAs and the preservation of several active copies indicate the importance of this post-transcriptional regulation, which allows the bacterium to increase its plasticity by rapidly adjusting its physiology in response to environmental constraints.  
The existence of multiple factors devoted to _rsm_ expression and degradation, illustrates that bacteria have evolved versatile mechanisms to control Rsm sRNAs levels. The higher expression level and the greater stability of the four Rsm sRNAs when nutrient conditions are limited underscore their relevance in the ecological niche of _P. brassicaearum_, a soil in which nutrients are poorly available. It is particularly interesting to note that this transcriptional activation of the four Rsm sRNAs occurs in concert with the increase in the intracellular level of the two signal molecules, (p)ppGpp and c-di-GMP under stringency conditions.  
The differences observed in expression and stability between the four Rsm sRNAs illustrate that the subtleties of their respective roles in bacterial adaptation to challenging conditions remain far from being completely understood, as well as the regulation network involving (p)ppGpp and c-diGMP. This definitively deserves to be investigated in further detail.  
Finally, although Rsm sRNA concentrations in the cell vary due to noise in gene expression and transcript stability, the overall combined concentrations of each Rsm sRNA are probably maintained in homeostatic balance.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/2076-260](https://www.mdpi.com/2076-260)]([https://www.mdpi.com/2076-260](https://www.mdpi.com/2076-260)) 7/9/2/250/s1. Table S1. Primers: plasmids and strains used in this study. Figure S1. Detection of protease activity under nutrient starvation conditions. (A) Wild-type and _gacA_ strains on TSA/20 lec, on TSA 1/10 lec and on undiluted TSA lec media. (B) Halo thickness (distance from bacteria to halo edge) is expressed as the mean of three measurements, in cm. lec means Skimmed milk (10/%) was added to growth medium. Figure S2. Rsm RNA stability. In vivo assay of Rsm RNA degradation of _P. brassicaearum_ NFM421 culture at exponential and stationary growth phases under nutrient replete and deplete conditions and rifampicin treatment. Samples were taken after 5, 15, 30, 45, 60, 90, 120,  
Figure 7: Model for gene regulation by ppGpp and c-di-GMP in the Gac-Rsm system of _P. brassicaearum_ NFM421. This pathway is supported by evidence from this work and previous studies ([PERSON] et al., 2012, [PERSON] et al., 2012, [PERSON] et al., 2020). \(\downarrow\), positive effect; \(\perp\), negative effect, dotted lines, indirect effects. The new conclusion of this study is that starvation conditions seem to activate the Gac-Rsm system concomitantly with the production of ppGpp and c-di-GMP.  
150 and 180 min for RNA extraction and q-RT-PCR analysis. Data were normalized to the values obtained from the analysis of 165 rRNA as an internal control.  
Conceptualization, D.L. and W.A.; D.L. performed DNA and RNA experiments; S.F. contributed to RNA decay experiments; M.H. performed metabolites analysis; P.O. performed phylogeny analysis; writing-original draft preparation, D.L.; writing-review and editing, W.A., T.H., M.H., P.O., P.S.-K. and D.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not Applicable.  
All data in this article is openly available without any restrictions.  
This work was supported by IRTELIS PhD program Grant from CEA.  
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.