Oxygen as a key developmental regulator of Rhizobium meliloti N2-fixation gene expression within the alfalfa root nodule.
The symbiotic pattern of expression of Rhizobium meliloti N2-fixation genes is tightly coupled with the histological organization of the alfalfa root nodule and thus is under developmental control. N2-fixation gene expression is induced very sharply at a particular zone of the nodule called interzone II-III that precedes the zone where N2 fixation takes place. We show here that this coupling can be disrupted, hereby resulting in ectopic expression of N2-fixation genes in the prefixing zone II of the nodule. Uncoupling was obtained either by using a R. meliloti strain in which a mutation rendered N2-fixation gene expression constitutive with respect to oxygen in free-living bacterial cultures or by placing nodules induced by a wild-type R. meliloti strain in a microoxic environment. These results implicate oxygen as a key determinant of the symbiotic pattern of N2-fixation gene expression.
Soupène
E
E
Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, Institut National de la Recherche Agronomique, Castanet Tolosan, France.
Foussard
M
M
Boistard
P
P
Truchet
G
G
Batut
J
J
D000332:Aerobiosis; D004594:Electrophysiology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D000455:Medicago sativa / Q000382:microbiology; D008839:Microelectrodes; D009586:Nitrogen Fixation / Q000235:genetics*; D010100:Oxygen / Q000378:metabolism; D018517:Plant Roots; D017354:Point Mutation; D015183:Restriction Mapping; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000502:physiology*
D010100:Oxygen