Caractérisation des bactériophytochromes identifiés chez Rhodopseudomas palustris et Bradyrhizobium

Rhodopseudomonas palustris is a photosynthetic purple bacteria which genome was completely sequenced. Six genes encoding putative bactériophytochromes are present in this genome. One of them plays an essential and unusual role in the synthesis of the photosystem. In this bacteria, three other bacteriophytochromes are localized near pucBA operons encoding polypeptides involved in the formation of light harvesting complexes associated with photosystem. First, this PhD work studied roles, properties and mechanisms of action of these three bacteriophytochromes. We showed that RpBphP2 and RpBphP3 act in tandem to regulate the expression of LH4 antennas. This signalling pathway use three reponse- regulators, one of them, Rpa3018 is rdox sensitive. In some strains of Rps. palustris, a bactériophytochrome, RpBphP4, lost its light sensitivity and acquired a redox sensibility while keeping its ability to regulate the expression of these antennas. In a second time, analysis of the genome sequence of two photosynthetic Bradyrhizobium (ORS278 and BTAi1) revealed, in each strain, the presence of a specific bacteriophytochrome probably acquired by horizontal transfer. The properties of these various bacteriophytochromes led highlighted the variety of this family of light sensors as well as the complexity of the signalling pathways which they introduce.Rhodopseudomonas palustris est une bactérie pourpre photosynthétique dont le génome, entièrement séquencé, a révélé avec surprise la présence de 6 gènes codant des bactériophytochromes. L'un d'entre eux (RpBphP1) joue un rôle primordial et inhabituel dans la synthèse du photosystème. Chez cette bactérie, trois autres bactériophytochromes (RpBphP2, 3 et 4) sont localisés à proximité d'opérons pucBA codant les polypeptides des antennes collectrices de lumière associées au photosystème. Ce travail de thèse a consisté dans un premier temps à étudier les rôles, les propriétés et les mécanismes d'action de ces 3 bactériophytochromes. Il a pu être ainsi montré que les 2 bactériophytochromes RpBphP2 et 3 agissent de concert dans le contrôle des antennes de types LH4. Cette voie de régulation implique l'action de 3 autres réponses-régulateurs dont la protéine Rpa3018 sensible au potentiel redox. Cette étude a également révélé que, chez certaines souches de Rps. palustris, la protéine RpBphP4 a perdu sa sensibilité à la lumière mais a acquis en contrepartie une sensibilité au potentiel redox tout en conservant sa capacité à réguler l'expression des antennes de type LH2 via un système à 2 composants. Dans un second temps, l'analyse de la séquence du génome de deux Bradyrhizobium photosynthétiques (ORS278 et BTAi1) a révélé que chaque souche possède un bactériophytochrome spécifique sûrement acquis par transfert horizontal. Les études menées sur ces différents bactériophytochromes ont mis en exergue la diversité de cette famille de senseurs de lumière ainsi que la complexité des voies de signalisation qu'ils initient

Caractérisation des bactériophytochromes identifiés chez Rhodopseudomonas palustris et bradyrhizobium

Rhodopseudomonas palustris est une bactérie pourpre photosynthétique dont le génome, entièrement séquencé, a révélé avec surprise la présence de 6 gènes codant des bactériophytochromes. L'un d'entre eux (RpBphP1) joue un rôle primordial et inhabituel dans la synthèse du photosystème. Chez cette bactérie, trois autres bactériophytochromes (RpBphP2, 3 et 4) sont localisés à proximité d'opérons pucBA codant les polypeptides des antennes collectrices de lumière associées au photosystème. Ce travail de thèse a consisté dans un premier temps à étudier les rôles, les propriétés et les mécanismes d'action de ces 3 bactériophytochromes. Il a pu être ainsi montré que les 2 bactériophytochromes RpBphP2 et 3 agissent de concert dans le contrôle des antennes de types LH4. Cette voie de régulation implique l'action de 3 autres réponses-régulateurs dont la protéine Rpa3018 sensible au potentiel redox. Cette étude a également révélé que, chez certaines souches de Rps. palustris, la protéine RpBphP4 a perdu sa sensibilité à la lumière mais a acquis en contrepartie une sensibilité au potentiel redox tout en conservant sa capacité à réguler l'expression des antennes de type LH2 via un système à 2 composants. Dans un second temps, l'analyse de la séquence du génome de deux Bradyrhizobium photosynthétiques (ORS278 et BTAi1) a révélé que chaque souche possède un bactériophytochrome spécifique sûrement acquis par transfert horizontal. Les études menées sur ces différents bactériophytochromes ont mis en exergue la diversité de cette famille de senseurs de lumière ainsi que la complexité des voies de signalisation qu'ils initientRhodopseudomonas palustris is a photosynthetic purple bacteria which genome was completely sequenced. Six genes encoding putative bactériophytochromes are present in this genome. One of them plays an essential and unusual role in the synthesis of the photosystem. In this bacteria, three other bacteriophytochromes are localized near pucBA operons encoding polypeptides involved in the formation of light harvesting complexes associated with photosystem. First, this PhD work studied roles, properties and mechanisms of action of these three bacteriophytochromes. We showed that RpBphP2 and RpBphP3 act in tandem to regulate the expression of LH4 antennas. This signalling pathway use three reponse-regulators, one of them, Rpa3018 is rdox sensitive. In some strains of Rps. palustris, a bactériophytochrome, RpBphP4, lost its light sensitivity and acquired a redox sensibility while keeping its ability to regulate the expression of these antennas. In a second time, analysis of the genome sequence of two photosynthetic Bradyrhizobium (ORS278 and BTAi1) revealed, in each strain, the presence of a specific bacteriophytochrome probably acquired by horizontal transfer. The properties of these various bacteriophytochromes led highlighted the variety of this family of light sensors as well as the complexity of the signalling pathways which they introduceMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Dual role for a bacteriophytochrome in the bioenergetic control of Rhodopsdeudomonas palustris : enhancement of photosystem synthesis and limitation of respiration

In the purple photosynthetic bacterium Rhodopseudomonas palustris, far-red illumination induces photosystem synthesis via the action of the bacteriophytochrome RpBphP1. This bacteriophytochrome antagonizes the repressive effect of the transcriptional regulator PpsR2 under aerobic condition. We show here that, in addition to photosystem synthesis, far-red light induces a significant growth rate limitation, compared to cells grown in the dark, linked to a decrease in the respiratory activity. The phenotypes of mutants inactivated in RpBphP1 and PpsR2 show their involvement in this regulation. Based on enzymatic and transcriptional studies, a 30% decrease in the expression of the alpha-ketoglutarate dehydrogenase complex, a central enzyme of the Krebs cycle, is observed under far-red light. We propose that this decrease is responsible for the down-regulation of respiration in this condition. This regulation mechanism at the Krebs cycle level still allows the formation of the photosynthetic apparatus via the synthesis of key biosynthesis precursors but lowers the production of NADH, i.e. the respiratory activity. Overall, the dual action of RpBphP1 on the regulation of both the photosynthesis genes and the Krebs cycle allows a fine adaptation of bacteria to environmental conditions by enhancement of the most favorable bioenergetic process in the light, photosynthesis versus respiration

A New Type of Bacteriophytochrome Acts in Tandem with a Classical Bacteriophytochrome to Control the Antennae Synthesis in Rhodopseudomonas palustris

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Legumes symbioses : absence of Nod genes in photosynthetic bradyrhizobia

Leguminous plants ( such as peas and soybeans) and rhizobial soil bacteria are symbiotic partners that communicate through molecular signaling pathways, resulting in the formation of nodules on legume roots and occasionally stems that house nitrogen-fixing bacteria. Nodule formation has been assumed to be exclusively initiated by the binding of bacterial, host-specific lipochito-oligosaccharidic Nod factors, encoded by the nodABC genes, to kinase-like receptors of the plant. Here we show by complete genome sequencing of two symbiotic, photosynthetic, Bradyrhizobium strains, BTAi1 and ORS278, that canonical nodABC genes and typical lipochito-oligosaccharidic Nod factors are not required for symbiosis in some legumes. Mutational analyses indicated that these unique rhizobia use an alternative pathway to initiate symbioses, where a purine derivative may play a key role in triggering nodule formation

Evolution of a bacteriophytochrome from light to redox sensor

Bacteriophytochromes are red/far-red photoreceptors that bacteria use to mediate sensory responses to their light environment. Here, we show that the photosynthetic bacterium Rhodopseudomonas palustris has two distinct types of bacteriophytochrome-related protein (RpBphP4) depending upon the strain considered. The first type binds the chromophore biliverdin and acts as a light-sensitive kinase, thus behaving as a bona fide bacteriophytochrome. However, in most strains, RpBphP4 does not to bind this chromophore. This loss of light sensing is replaced by a redox-sensing ability coupled to kinase activity. Phylogenetic analysis is consistent with an evolutionary scenario, where a bacteriophytochrome ancestor has adapted from light to redox sensing. Both types of RpBphP4 regulate the synthesis of light harvesting (LH2) complexes according to the light or redox conditions, respectively. They modulate the affinity of a transcription factor binding to the promoter regions of LH2 complex genes by controlling its phosphorylation status. This is the first complete description of a bacteriophytochrome signal transduction pathway involving a two-component system