![]() ![]() In-frame deletion mutants of these 9 homologs were constructed. We chose the top 9 homologs (in terms of identity), which share 37.79% to 42.63% identity with RpfR, for further study (Supplementary Data 2). solanacearum GMI1000 by using the Basic Local Alignment Search Tool (BLAST) algorithm ( ). solanacearum, we performed a homology search for RpfR from Burkholderia cenocepacia H111 in R. To investigate the potential bis-3′,5′-c-di-GMP signaling system in R. Our previous studies demonstrated that RpfR, which contains Per/Arnt/Sim (PAS)-GGDEF-EAL domains, is an important metabolic enzyme of bis-3′,5′-c-di-GMP that can sense both BDSF and bis-3′,5′-c-di-GMP 23. solanacearum possesses various GGDEF and EAL domain-containing proteins (Supplementary Data 1), which led us to investigate whether it employs bis-3′,5′-c-di-GMP or any other nucleotide second messenger. RSp0334 controls important biological functions in R. We also found that homologs of both RSp0334 and RSp0980 and intracellular 2′,3′-cGMP are present in the human pathogen Salmonella typhimurium, suggesting that the RSp0334/2′,3′-cGMP/RSp0980 signaling system is not solely existed in R. solanacearum caused an increase in the intracellular level of 2′,3′-cGMP, which binds to its receptor RSp0980 and abolishes the interaction between RSp0980 and the promoters of target genes, ultimately impairing biofilm formation, motility, virulence and the production of QS signals. In this study, we identified a protein, RSp0334, which contains a specific LLARLGGDQF motif that converts two 2′,3′-cyclic guanosine monophosphate (2′,3′-cGMP) molecules to one (2′,5′)(3′,5′)-cyclic diguanosine monophosphate (2′,3′-c-di-GMP) molecule. It was found that RpfR of Burkholderia cenocepacia is a QS signal receptor that also functions as a bis-3′,5′-c-di-GMP sensor 22, 23, suggesting that bacterial pathogens use both intracellular and extracellular signals to integrate information about the physical and chemical surroundings and their population density to control their physiology and virulence characteristics. Intriguingly, there is growing evidence that bacteria integrate QS and bis-3′,5′-c-di-GMP signaling to control biological functions. To date, multiple QS signals have been identified in bacterial species, and recently, a common metabolic product, anthranilic acid, was revealed to be used as a bacterial signal 20, 21. Quorum sensing (QS) signals are extracellular signaling molecules employed by many bacterial species to coordinate group behaviors in response to cell density 18, 19. Various families of bis-3′,5′-c-di-GMP effectors have been identified and characterized to date, including PilZ domain proteins 4, 11, degenerate GGDEF or EAL domain proteins 12, 13, transcriptional regulators 14, 15, mRNA riboswitches 16, and elongation factor P 17. The bis-3′,5′-c-di-GMP signal transduction systems provide bacteria with the ability to sense changes in cell status or environmental conditions and execute appropriate physiological and social behaviors in response 10. This second messenger is synthesized by diguanylate cyclases (DGCs characterized by GGDEF domains) from two GTPs and degraded by specific phosphodiesterases (PDEs containing either EAL or HD-GYP domains) 7, 8, 9. Since then, bis-3′,5′-c-di-GMP has been shown to control a variety of cellular processes in bacteria 4, 5, 6. It was first found in Acetobacter xylinum, in which it is involved in the regulation of cellulose synthesis 3. Among them, bis-(3′,5′)-cyclic diguanosine monophosphate (bis-3′,5′-c-di-GMP) has been found to be used as a second messenger in all major bacterial phyla 2. Nucleotide second messengers are a class of intracellular signaling molecules 1. Together, our work provides insights into the unusual function of the GGDEF domain of RSp0334 and the special regulatory mechanism of 2',3'-cGMP signal in bacteria. Furthermore, we found that 2',3'-cGMP, its receptor and the evolved GGDEF domain with a LLARLGGDEF motif also exist in the human pathogen Salmonella typhimurium. In-frame deletion of RSp0334, which contains an evolved GGDEF domain with a LLARLGGDQF motif required to catalyze 2',3'-cGMP to (2',5')(3',5')-cyclic diguanosine monophosphate (2',3'-c-di-GMP), altered the abovementioned important phenotypes through increasing the intracellular 2',3'-cGMP levels. This signal specifically binds to RSp0980 with high affinity and thus abolishes the interaction between RSp0980 and the promoters of target genes. Here, we report that 2',3'-cyclic guanosine monophosphate (2',3'-cGMP) controls the important biological functions, quorum sensing (QS) signaling systems and virulence in Ralstonia solanacearum through the transcriptional regulator RSp0980. Previous studies have demonstrated that bis-(3',5')-cyclic diguanosine monophosphate (bis-3',5'-c-di-GMP) is a ubiquitous second messenger employed by bacteria. ![]()
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