THE ALPHA-PROTEOBACTERIAL TRANS-ENCODED SMALL RNA MMGR: PROTEOMIC PROFILING REVEALS ROLE BEYOND POLYHYDROXYBUTYRATE REGULATION IN SINORHIZOBIUM MELILOTI

ANTONIO LAGARES JR.; TIMO GLATTER; CLAUDIO VALVERDE; ANKE BECKER

Nápoles

Conferencia; 15th European Nitrogen Fixation Conference; 2023

In the N2-fixing legume symbiont S. meliloti, mmgR encodes a 77-nt non-coding sRNA[1]. mmgR evolves from a common ancestor of the α-proteobacteria that diverged from the order of Rickettsiales, thus being so far the sRNA with the widest phylogenetic distribution described in this bacterial clade[2]. mmgR orthologs –grouped after a strong microsyntheny found with a conserved protein coding gene- share fully conserved structure and sequence traits along evolution. MmgR regulates the production of the major C- and reducing-power-storage polymer polyhydroxybutyrate (PHB) in S. meliloti cells growing under conditions of N starvation and C surplus. MmgR expression in S. meliloti sets a limit for PHB accumulation and modulates PHB-granule morphology[3]. The expression of MmgR is mainly regulated at the transcriptional level by the N and C metabolism master regulators NtrC and AniA, respectively[4, 5]. This regulation relies on a conserved dyadic motif located within the -35 and -10 boxes of the mmgR promoter, and results in activation of mmgR expression according to the C:N molar ratio in the growth medium upon exhaustion of the N source. MmgR is part of a regulatory loop that operates to maintain a proper structure and amount of PHB granules in S. meliloti through a fine-tuning of the intracellular levels of phasins and polymer, on the basis of the availability of N and C.Here, we profiled the proteome of S. meliloti during growth in defined medium to dynamically follow the changes associated with modifying the intracellular activity of MmgR. We found that MmgR impacts on multiple targets beyond its known role in the regulation of PHB metabolism, which suggests its role as a regulatory hub associated with the transition phase to nutrient scarce conditions.