Expression of the Sinorhizobium meliloti small RNA gene mmgR is controlled by the nitrogen source

CEIZEL BORELLA, GERMÁN ; LAGARES, ANTONIO; VALVERDE, CLAUDIO

FEMS MICROBIOLOGY LETTERS

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016

0378-1097

Según consta en la publicación original, los autores Ceizel Borella Germán y Lagares Antonio Jr. contribuyeron por igual a este trabajo.Small non-coding RNAs (sRNAs) are key players in post-transcriptional regulation of gene expression. Hundreds of sRNAs have been identified in Sinorhizobium meliloti but their biological function remains unknown for most of them. In this study, we characterized the expression pattern of the gene encoding the 77-nt sRNA MmgR in S. meliloti strain 2011. A chromosomal transcriptional reporter fusion (PmmgR-gfp) showed that the mmgR promoter is active along different stages of the interaction with alfalfa roots. In vitro, PmmgR-gfp activity paralleled the sRNA abundance indicating that mmgR expression is primarily controlled at the level of transcriptional initiation. PmmgR-gfp activity was higher during growth in RDM medium than in TY medium. Furthermore, PmmgR-gfp was induced at 60 min after shifting growing cells from TY to RDM medium, i.e., faster than the cell doubling time. In defined RDM medium containing NO3−, both PmmgR-gfp and MmgR level were repressed by addition of tryptone or single amino acids, suggesting that mmgR expression depends on the cellular N status. In silico analysis failed to detect conserved motifs upstream the promoter RNA polymerase binding site, but revealed a strongly conserved motif centered at -28, which may be linked to the observed regulatory pattern by the nitrogen source.