The Sinorhizobium meliloti EmrR regulator is required for efficient colonization of Medicago sativa root nodules.
Mol Plant Microbe Interact, 2014/4;27(4):388-99.
Santos MR, Marques AT, Becker JD, Moreira LM
PMID: 24593245DOI: 10.1094/MPMI-09-13-0284-R
Impact factor: 3.422
Abstract
The nitrogen-fixing bacterium Sinorhizobium meliloti must adapt to diverse conditions encountered during its symbiosis with leguminous plants. We characterized a new symbiotically relevant gene, emrR (SMc03169), whose product belongs to the TetR family of repressors and is divergently transcribed from emrAB genes encoding a putative major facilitator superfamily-type efflux pump. An emrR deletion mutant produced more succinoglycan, displayed increased cell-wall permeability, and exhibited higher tolerance to heat shock. It also showed lower tolerance to acidic conditions, a reduced production of siderophores, and lower motility and biofilm formation. The simultaneous deletion of emrA and emrR genes restored the mentioned traits to the wild-type phenotype, except for survival under heat shock, which was lower than that displayed by the wild-type strain. Furthermore, the ΔemrR mutant as well as the double ΔemrAR mutant was impaired in symbiosis with Medicago sativa; it formed fewer nodules and competed poorly with the wild-type strain for nodule colonization. Expression profiling of the ΔemrR mutant showed decreased expression of genes involved in Nod-factor and rhizobactin biosynthesis and in stress responses. Expression of genes directing the biosynthesis of succinoglycan and other polysaccharides were increased. EmrR may therefore be involved in a regulatory network targeting membrane and cell wall modifications in preparation for colonization of root hairs during symbiosis.
MeSH terms
Amino Acid Sequence; Bacterial Adhesion; Bacterial Proteins; Biofilms; Gene Deletion; Gene Expression Regulation, Bacterial; Medicago sativa; Movement; Plant Root Nodulation; Sinorhizobium meliloti
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