Open AccessMucR Is Necessary for Galactoglucan Production in Sinorhizobium meliloti EFB1
Author(s) -
Marta Martín,
Javier Lloret,
María Sánchez-Contreras,
Ildefonso Bonilla,
Rafael Rivilla
Publication year - 2000
Publication title -
molecular plant-microbe interactions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.565
H-Index - 153
eISSN - 1943-7706
pISSN - 0894-0282
DOI - 10.1094/mpmi.2000.13.1.129
Subject(s) - sinorhizobium meliloti , mutant , repressor , biology , promoter , gene , heterologous , strain (injury) , lac operon , genetics , mutation , heterologous expression , gene expression , sinorhizobium , rhizobiaceae , bacteria , symbiosis , recombinant dna , anatomy
Sinorhizobium meliloti can produce two types of acidic exopolysaccharides, succinoglycan and galactoglucan, that are interchangeable for infection of alfalfa nodules. Strain SU47 and derivatives produce only succinoglycan, unless it grows under phosphate limitation or carries a mutation in either of two regulatory loci, mucR or expR. It has been proposed that MucR acts as a transcriptional repressor that blocks the expression of the exp genes responsible for galactoglucan production. Strain EFB1 simultaneously produces both exopolysaccharides. Heterologous expression of lacZ transcriptional fusions of the expE promoters has shown that genetic background is more important that promoter sequence for exp gene expression, since expE promoters from both strains are expressed at high level in EFB1 and not in SU47. We have found that mucR is present in mucoid and nonmucoid strains, and in EFB1 differs from SU47 in only one conservative amino acid change. MucR proteins from both strains are interchangeable. An mucR mutant of EFB1 cannot produce galactoglucan and does not express mucS.