Bacteriophytochrome controls photosystem synthesis in anoxygenic bacteria.
Plants use a set of light sensors to control their growth and development in response to changes in ambient light. In particular, phytochromes exert their regulatory activity by switching between a biologically inactive red-light-absorbing form (Pr) and an active far-red-light absorbing form (Pfr). Recently, biochemical and genetic studies have demonstrated the occurrence of phytochrome-like proteins in photosynthetic and non-photosynthetic bacteria--but little is known about their functions. Here we report the discovery of a bacteriophytochrome located downstream from the photosynthesis gene cluster in a Bradyrhizobium strain symbiont of Aeschynomene. The synthesis of the complete photosynthetic apparatus is totally under the control of this bacteriophytochrome. A similar behaviour is observed for the closely related species Rhodopseudomonas palustris, but not for the more distant anoxygenic photosynthetic bacteria of the genus Rhodobacter, Rubrivivax or Rhodospirillum. Unlike other (bacterio)phytochromes, the carboxy-terminal domain of this bacteriophytochrome contains no histidine kinase features. This suggests a light signalling pathway involving direct protein-protein interaction with no phosphorelay cascade. This specific mechanism of regulation may represent an important ecological adaptation to optimize the plant-bacteria interaction.
Giraud
Eric
E
LSTM TA 10/J Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR 113, IRD/CIRAD/INRA/ENSA-M. Campus de Baillarguet, 34398 Montpellier Cedex 5, France.
Fardoux
Joël
J
Fourrier
Nicolas
N
Hannibal
Laure
L
Genty
Bernard
B
Bouyer
Pierre
P
Dreyfus
Bernard
B
Verméglio
André
A
D000042:Absorption / Q000528:radiation effects; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020369:Bradyrhizobium / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D005798:Genes, Bacterial / Q000235:genetics; D008027:Light; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009154:Mutation / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000528:radiation effects; D010858:Pigmentation; D010860:Pigments, Biological / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D010860:Pigments, Biological; D010100:Oxygen