Affiliation:
1. Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688
Abstract
ABSTRACT
A successful symbiotic relationship between
Sinorhizobium meliloti
and its host
Medicago sativa
(alfalfa) depends on several signaling mechanisms, such as the biosynthesis of exopolysaccharides (EPS) by
S. meliloti
. Previous work in our laboratory has shown that a quorum-sensing mechanism controls the production of the symbiotically active EPS II. Recent microarray analysis of the whole-genome expression profile of
S. meliloti
reveals that the ExpR/Sin quorum-sensing system regulates additional physiological processes that include low-molecular-weight succinoglycan production, nitrogen utilization, metal transport, motility, and chemotaxis. Nearly half of the flagellar genes and their dependence on quorum sensing are prominently displayed in our microarray analyses. We extend those observations in this work and confirm the findings by real-time PCR expression analysis of selected genes, including the
flaF, flbT, flaC, cheY1
, and
flgB
genes, involved in motility and chemotaxis. These genes code for regulators of flagellum synthesis, the chemotactic response, or parts of the flagellar apparatus. Gene expression analyses and visualization of flagella by electron microscopy performed at different points in the growth phase support our proposed model in which quorum sensing downregulates motility in
S. meliloti
. We demonstrate that the ExpR/Sin quorum-sensing system controls motility gene expression through the VisN/VisR/Rem relay. We also show that the ExoS-dependent two-component system suppresses motility gene expression through VisN and Rem in parallel to quorum sensing. This study contributes to our understanding of the mechanisms that govern motility in
S. meliloti
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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