The Sinorhizobium meliloti EmrR regulator is required for efficient colonization of Medicago sativa root nodules.

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.

• Authors: Mário R Santos, Andreia T Marques, Jörg D Becker, Leonilde M Moreira
• Journal: Molecular plant-microbe interactions : MPMI (Mol Plant Microbe Interact) Vol. 27 Issue 4 Pg. 388-99 (Apr 2014) ISSN: 0894-0282 [Print] United States
• PMID: 24593245 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Bacterial Proteins

Topics

• Amino Acid Sequence
• Bacterial Adhesion (physiology)
• Bacterial Proteins (genetics, metabolism)
• Biofilms
• Gene Deletion
• Gene Expression Regulation, Bacterial (physiology)
• Medicago sativa (microbiology)
• Movement
• Plant Root Nodulation (physiology)
• Sinorhizobium meliloti (genetics, metabolism)