Light and redox control of photosynthesis gene expression in Bradyrhizobium: dual roles of two PpsR.
The two closely related bacteria Bradyrhizobium and Rhodopseudomonas palustris show an unusual mechanism of regulation of photosystem formation by light thanks to a bacteriophytochrome that antirepresses the regulator PpsR. In these two bacteria, we found out, unexpectedly, that two ppsR genes are present. We show that the two Bradyrhizobium PpsR proteins exert antagonistic effects in the regulation of photosystem formation with a classical repressor role for PpsR2 and an unexpected activator role for PpsR1. DNase I footprint analysis show that both PpsR bind to the same DNA TGTN12ACA motif that is present in tandem in the bchC promoter and the crtED intergenic region. Interestingly, the cycA and aerR promoter regions that contain only one conserved palindrome are recognized by PpsR2, but not PpsR1. Further biochemical analyses indicate that PpsR1 only is redox sensitive through the formation of an intermolecular disulfide bond, which changes its oligomerization state from a tetramer to an octamer under oxidizing conditions. Moreover, PpsR1 presents a higher DNA affinity under its reduced form in contrast to what has been previously found for PpsR or its homolog CrtJ from the Rhodobacter species. These results suggest that regulation of photosystem synthesis in Bradyrhizobium involves two PpsR competing for the binding to the same photosynthesis genes and this competition might be modulated by two factors: light via the antagonistic action of a bacteriophytochrome on PpsR2 and redox potential via the switch of PpsR1 oligomerization state.
Laboratoire des Symbioses Tropicales et Méditerranéennes (UMR113-IRD-CIRAD-AGRO-M-INRA-UM2), TA 10/J, Campus de Baillarguet, 34398 Montpellier 5, France.
Marianne
M
Jaubert
Sébastien
S
Zappa
Joël
J
Fardoux
Jean-Marc
JM
Adriano
Laure
L
Hannibal
Sylvie
S
Elsen
Jérome
J
Lavergne
Andre
A
Verméglio
Eric
E
Giraud
David
D
Pignol
D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology; D001483:Base Sequence; D020369:Bradyrhizobium / Q000378:metabolism*; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology; D003850:Deoxyribonuclease I / Q000737:chemistry / Q000378:metabolism; D004220:Disulfides; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D008024:Ligands; D008027:Light; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012097:Repressor Proteins / Q000737:chemistry* / Q000502:physiology; D016992:Rhodobacter / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D004220:Disulfides; D008024:Ligands; D012097:Repressor Proteins; D004247:DNA; D003850:Deoxyribonuclease I; D001616:beta-Galactosidase; D010100:Oxygen; D004229:Dithiothreitol