Multiple sensors provide spatiotemporal oxygen regulation of gene expression in a Rhizobium-legume symbiosis
| Autor: | Graham A. Hood, Philip S. Poole, Harrison Steel, Paul J. Rutten, Barney A. Geddes, Antonis Papachristodoulou, Vinoy K. Ramachandran, Lucie McMurtry |
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| Rok vydání: | 2021 |
| Předmět: |
0106 biological sciences
Cancer Research Histidine Kinase Physiology Gene Expression Artificial Gene Amplification and Extension Plant Science QH426-470 medicine.disease_cause Biochemistry Polymerase Chain Reaction 01 natural sciences Transcription (biology) Nucleic Acids Gene expression Genetics (clinical) Regulation of gene expression 0303 health sciences biology Fabaceae Cell biology Chemistry Plant Physiology Physical Sciences Rhizobium Research Article Chemical Elements Research and Analysis Methods Rhizobium leguminosarum Rhizobia 03 medical and health sciences Bacterial Proteins Symbiosis Nitrogen Fixation DNA-binding proteins Operon Genetics medicine Gene Regulation Operons Molecular Biology Techniques Molecular Biology Transcription factor Ecology Evolution Behavior and Systematics 030304 developmental biology Biology and Life Sciences Proteins DNA Gene Expression Regulation Bacterial biology.organism_classification Regulatory Proteins Oxygen Species Interactions Mutation Transcription Factors 010606 plant biology & botany |
| Zdroj: | PLoS Genetics PLoS Genetics, Vol 17, Iss 2, p e1009099 (2021) |
| ISSN: | 1553-7404 |
| Popis: | Regulation by oxygen (O2) in rhizobia is essential for their symbioses with plants and involves multiple O2 sensing proteins. Three sensors exist in the pea microsymbiont Rhizobium leguminosarum Rlv3841: hFixL, FnrN and NifA. At low O2 concentrations (1%) hFixL signals via FxkR to induce expression of the FixK transcription factor, which activates transcription of downstream genes. These include fixNOQP, encoding the high-affinity cbb3-type terminal oxidase used in symbiosis. In free-living Rlv3841, the hFixL-FxkR-FixK pathway was active at 1% O2, and confocal microscopy showed hFixL-FxkR-FixK activity in the earliest stages of Rlv3841 differentiation in nodules (zones I and II). Work on Rlv3841 inside and outside nodules showed that the hFixL-FxkR-FixK pathway also induces transcription of fnrN at 1% O2 and in the earliest stages of Rlv3841 differentiation in nodules. We confirmed past findings suggesting a role for FnrN in fixNOQP expression. However, unlike hFixL-FxkR-FixK, Rlv3841 FnrN was only active in the near-anaerobic zones III and IV of pea nodules. Quantification of fixNOQP expression in nodules showed this was driven primarily by FnrN, with minimal direct hFixL-FxkR-FixK induction. Thus, FnrN is key for full symbiotic expression of fixNOQP. Without FnrN, nitrogen fixation was reduced by 85% in Rlv3841, while eliminating hFixL only reduced fixation by 25%. The hFixL-FxkR-FixK pathway effectively primes the O2 response by increasing fnrN expression in early differentiation (zones I-II). In zone III of mature nodules, near-anaerobic conditions activate FnrN, which induces fixNOQP transcription to the level required for wild-type nitrogen fixation activity. Modelling and transcriptional analysis indicates that the different O2 sensitivities of hFixL and FnrN lead to a nuanced spatiotemporal pattern of gene regulation in different nodule zones in response to changing O2 concentration. Multi-sensor O2 regulation is prevalent in rhizobia, suggesting the fine-tuned control this enables is common and maximizes the effectiveness of the symbioses. Author summary Rhizobia are soil bacteria that form a symbiosis with legume plants. In exchange for shelter from the plant, rhizobia provide nitrogen fertilizer, produced by nitrogen fixation. Fixation is catalysed by the nitrogenase enzyme, which is inactivated by oxygen. To prevent this, plants house rhizobia in root nodules, which create a low oxygen environment. However, rhizobia need oxygen, and must adapt to survive the low oxygen concentration in the nodule. Key to this is regulating their genes based on oxygen concentration. We studied one Rhizobium species which uses three different protein sensors of oxygen, each turning on at a different oxygen concentration. As the bacteria get deeper inside the plant nodule and the oxygen concentration drops, each sensor switches on in turn. Our results also show that the first sensor to turn on, hFixL, primes the second sensor, FnrN. This prepares the rhizobia for the core region of the nodule where oxygen concentration is lowest and most nitrogen fixation takes place. If both sensors are removed, the bacteria cannot fix nitrogen. Many rhizobia have several oxygen sensing proteins, so using multiple sensors is likely a common strategy enabling rhizobia to adapt to low oxygen precisely and in stages during symbiosis. |
| Databáze: | OpenAIRE |
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