The Rhizobium etli response regulator CenR is essential for both: Free-life and the rhizobial nitrogen-fixing symbiosis

• DOI: 10.1016/j.micres.2025.128159
• Publication Date: 2025-03-31T14:06:12Z
• Authors: María M. Banda; M.P. Elizabeth Sa...; Marisa Rodríguez; Sofía Martínez-Ab...; Alfonso Leija-Salas; Rocío Reyero-Saav...; Mishael Sánchez-P...; Georgina Hernández; Dimitris Georgellis; Ayari Fuentes-Her...; Lourdes Girard

The canonical two-component systems (TCS) consist of a histidine kinase and response regulator that work together to control various pathways in bacteria. Rhizobia are rod-shaped, Gram-negative alpha-proteobacteria capable establishing nitrogen-fixing symbiosis with compatible legume hosts. These bacteria can live freely the soil or as intracellular symbionts within root nodules. Here, we characterized an orphan OmpR-type Rhizobium etli CE3, which renamed CenR due its similarity proteins known essential regulators cell envelope-related functions alpha-proteobacteria. We identified cognate encoded by cenK, located separate genomic region from cenR. CenK form TCS has not been previously reported Rhizobium. Our results indicate overexpression cenR well absence negatively impacts R. growth morphology, while overexpressing also exhibit uncoordinated division. Furthermore, demonstrated CenKR directly indirectly regulates expression genes involved morphology. Electrophoretic mobility shift assays confirmed binds promoter regions two uncharacterized etli. analysis - common bean (Phaseolus vulgaris) revealed increased infection threads, reduced leghemoglobin content, lower nitrogen fixation efficiency nodules infected cenR-overexpressing strain. In conclusion, our findings coordinates important cycle events vital for both free-living symbiotic conditions.