biostudies-literatureGurich NNIGMS NIH HHS4372-82https://www.ebi.ac.uk/biostudies/studies/S-EPMC2698488biostudies-literatureUnknown191(13)The ExpR/Sin quorum-sensing system of the gram-negative soil bacterium Sinorhizobium meliloti plays an important role in the establishment of symbiosis with its host plant Medicago sativa. A mutant unable to produce autoinducer signal molecules (sinI) is deficient in its ability to invade the host, but paradoxically, a strain lacking the quorum-sensing transcriptional regulator ExpR is as efficient as the wild type. We compared the whole-genome expression profile of the wild-type strain with strains missing one of the quorum-sensing regulatory components to identify genes controlled by the ExpR/Sin system throughout the different phases of the bacterial growth cycle, as well as in planta. Our analyses revealed that ExpR is a highly versatile regulator with a unique ability to show differenJournal of bacteriologyRole of quorum sensing in Sinorhizobium meliloti-Alfalfa symbiosis.PMC2698488R01 GM0699251R01GM069925Gurich NGonzalez JEfalseRole of quorum sensing in Sinorhizobium meliloti-Alfalfa symbiosis.The ExpR/Sin quorum-sensing system of the gram-negative soil bacterium Sinorhizobium meliloti plays an important role in the establishment of symbiosis with its host plant Medicago sativa. A mutant unable to produce autoinducer signal molecules (sinI) is deficient in its ability to invade the host, but paradoxically, a strain lacking the quorum-sensing transcriptional regulator ExpR is as efficient as the wild type. We compared the whole-genome expression profile of the wild-type strain with strains missing one of the quorum-sensing regulatory components to identify genes controlled by the ExpR/Sin system throughout the different phases of the bacterial growth cycle, as well as in planta. Our analyses revealed that ExpR is a highly versatile regulator with a unique ability to show differen2009-01-01T00:00:00Z2009 Jul2025-04-26T00:34:54.637Z2019-03-27T00:23:02ZS-EPMC26984881939548810.1128/JB.00376-0910.1128/jb.00376-09