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A Sinorhizobium meliloti osmosensory two‐component system required for cyclic glucan export and symbiosis
Author(s) -
Griffitts Joel S.,
Carlyon Rebecca E.,
Erickson Jacob H.,
Moulton Jason L.,
Barnett Melanie J.,
Toman Carol J.,
Long Sharon R.
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2008.06304.x
Subject(s) - biology , sinorhizobium meliloti , mutant , microbiology and biotechnology , response regulator , transcription (linguistics) , transcriptome , extracellular , gene expression , motility , gene , ectopic expression , regulation of gene expression , phenotype , biochemistry , linguistics , philosophy
Summary A screen for novel symbiotic mutants of the nitrogen‐fixing legume symbiont Sinorhizobium meliloti uncovered a crucial role for the putative response regulator FeuP in the symbiotic infection process. Transcriptome analysis shows that FeuP controls the transcription of at least 16 genes, including ndvA , which encodes an ATP‐dependent exporter of cyclic β glucans. Loss of feuP function gives rise to traits associated with cyclic β glucan biosynthetic defects, including poor growth and motility under hypoosmotic conditions, and the inability to invade plant tissue during the early stages of symbiotic infection. Analysis of cyclic glucans indicates that the feuP mutant is able to synthesize intracellular cyclic β glucans, but is unable to export them. Cyclic β glucan export can be restored to feuP mutant cells by constitutive expression of ndvA ; likewise, the symbiotic phenotype of a feuP mutant is rescued by ectopic ndvA expression. We further show that the linked sensor kinase gene, feuQ , is also important for modulating ndvA transcription, and that signalling through the FeuP/FeuQ pathway is responsive to extracellular osmotic conditions, with low osmolarity stimulating ndvA expression.