A multi-sensor system provides spatiotemporal oxygen regulation of gene expression in a Rhizobium-legume symbiosis

摘要: Abstract Regulation by oxygen (O2) in rhizobia is essential for their symbioses with plants and involves multiple O2 sensing proteins. Three sensors exist the pea microsymbiont Rhizobium leguminosarum Rlv3841: hFixL, FnrN NifA. At low concentrations (1%) hFixL signals via FxkR to induce expression of FixK transcription factor, which activates downstream genes. These include fixNOQP, encoding high-affinity cbb3-type terminal oxidase used symbiosis. In vitro, Rlv3841 hFixL-FxkR-FixK cascade was active at 1% O2, confocal microscopy showed earliest stages differentiation nodules (zones I-II). vitro vivo work that also induces fnrN nodules. We confirmed past findings suggesting a role fixNOQP expression. However, unlike hFixL-FxkR-FixK, only near-anaerobic zones III-IV Quantification this driven primarily FnrN, minimal direct induction. Thus, key full symbiotic fixNOQP. Without nitrogen fixation reduced 85% Rlv3841, while eliminating 25%. The system effectively primes response increasing early Zone III mature nodules, conditions activate level required achieve wild-type activity. Modelling transcriptional analysis indicates different sensitivities lead nuanced spatiotemporal pattern gene regulation nodule changing concentration. Multi-sensor systems are prevalent rhizobia, fine-tuned control they enable common maximizes effectiveness symbioses. Author Summary Rhizobia soil bacteria form symbiosis legume plants. exchange shelter from plant, provide fertilizer, produced fixation. Fixation catalysed nitrogenase enzyme, inactivated oxygen. To prevent this, house root create environment. need oxygen, must adapt survive nodule. Key regulating genes based on studied one species uses three protein each turning As get deeper inside plant concentration drops, sensor switches turn. Our results show first turn on, second sensor, FnrN. This prepares core region where lowest most takes place. If both removed, cannot fix nitrogen. Many have several proteins, so using likely strategy makes it possible gradually during