000163309 001__ 163309 000163309 005__ 20251024172259.0 000163309 0247_ $$2doi$$a10.1128/spectrum.02311-25 000163309 0248_ $$2sideral$$a145757 000163309 037__ $$aART-2025-145757 000163309 041__ $$aeng 000163309 100__ $$0(orcid)0000-0002-0474-255X$$aGuío, Jorge 000163309 245__ $$aNsrM (All0345) and NsrX (Alr1976), two FurC (PerR)-targeted transcriptional regulators, modulate nitrogen metabolism and heterocyst differentiation genes in the cyanobacterium <i>Anabaena</i> sp. strain PCC 7120 000163309 260__ $$c2025 000163309 5060_ $$aAccess copy available to the general public$$fUnrestricted 000163309 5203_ $$aThe control of nitrogen metabolism in the model cyanobacterium Anabaena sp. strain PCC7120 is a complex process orchestrated by master regulators such as NtcA, HetR, and FurC (PerR). These proteins establish complex networks with secondary regulators, finely tuning cellular metabolism in response to diverse, often undefined environmental signals. The XRE-like Alr1976 and the MerR-like All0345 proteins are two predicted transcriptional regulators regulated by FurC. While All0345 is widespread, both proteins have homologs conserved across several bacterial phyla, with alr1976 often followed by a gene encoding a Zn-metalloprotease. Previous transcriptomic analyses showed that furC overexpression affected alr1976 expression slightly more under nitrogen-deficient conditions, while changes in all0345 expression were exclusively observed under N deficiency, pointing them as critical candidates for understanding the finer details of nitrogen control in Anabaena. This work shows that both Alr1976 (NsrX) and All0345 (NsrM) are potentially modulated by NtcA and work as nitrogen secondary regulators. Electrophoretic mobility shift assays and transcriptomic analyses of ∆nsrX and ∆nsrM deletion strains indicate that both regulators act as repressors of key genes involved in nitrogen metabolism and heterocyst development. Notably, the ∆nsrM strain showed earlier heterocyst formation at 24 h of nitrogen step-down. NsrX and NsrM display distinct requirements for optimal DNA-binding activity to nitrogen metabolism genes (presence of Mn and reducing environment, respectively), suggesting they respond to different environmental stimuli. This differential signal integration likely enables master regulators FurC and NtcA to exert more precise control over shared targets, thereby refining the intricate network of nitrogen metabolic regulation in Anabaena. 000163309 536__ $$9info:eu-repo/grantAgreement/ES/AEI/PID2023-146337NB-I00$$9info:eu-repo/grantAgreement/ES/DGA/E35-23R$$9info:eu-repo/grantAgreement/ES/MCIU/PID2019-104889GB-I00 000163309 540__ $$9info:eu-repo/semantics/openAccess$$aby$$uhttps://creativecommons.org/licenses/by/4.0/deed.es 000163309 655_4 $$ainfo:eu-repo/semantics/article$$vinfo:eu-repo/semantics/publishedVersion 000163309 700__ $$aAcero, Marta$$uUniversidad de Zaragoza 000163309 700__ $$aBandyopadhyay, Anindita 000163309 700__ $$aLiu, Deng 000163309 700__ $$aPakrasi, Himadri B. 000163309 700__ $$aMichaud-Soret, Isabelle 000163309 700__ $$0(orcid)0000-0002-8181-2689$$aBes, M. Teresa$$uUniversidad de Zaragoza 000163309 700__ $$0(orcid)0000-0001-6435-3540$$aSevilla, Emma$$uUniversidad de Zaragoza 000163309 700__ $$0(orcid)0000-0001-8644-4574$$aFillat, María F.$$uUniversidad de Zaragoza 000163309 7102_ $$11002$$2412$$aUniversidad de Zaragoza$$bDpto. Bioq.Biolog.Mol. Celular$$cÁrea Fisiología Vegetal 000163309 7102_ $$11002$$2060$$aUniversidad de Zaragoza$$bDpto. Bioq.Biolog.Mol. Celular$$cÁrea Bioquímica y Biolog.Mole. 000163309 773__ $$g(2025), [19 pp.]$$pMicrobiol. spectr.$$tMicrobiology Spectrum$$x2165-0497 000163309 8564_ $$s3473361$$uhttps://zaguan.unizar.es/record/163309/files/texto_completo.pdf$$yVersión publicada 000163309 8564_ $$s2324358$$uhttps://zaguan.unizar.es/record/163309/files/texto_completo.jpg?subformat=icon$$xicon$$yVersión publicada 000163309 909CO $$ooai:zaguan.unizar.es:163309$$particulos$$pdriver 000163309 951__ $$a2025-10-24-16:56:53 000163309 980__ $$aARTICLE