OnfD, an AraC-Type Transcriptional Regulator Encoded by Rhizobium tropici CIAT 899 and Involved in Nod Factor Synthesis and Symbiosis
|Author/s||Cerro Sánchez, Pablo del
Ayala García, Paula
Buzón García, Pablo
Castells Graells, Roger
López Baena, Francisco Javier
Ollero Márquez, Francisco Javier
Pérez Montaño, Francisco de Asís
|Department||Universidad de Sevilla. Departamento de Microbiología|
|Abstract||Rhizobium tropici CIAT 899 is a broad-host-range rhizobial strain that establishes symbiotic interactions with legumes and tolerates different environmental stresses such as heat, acidity, or salinity. This rhizobial strain ...
Rhizobium tropici CIAT 899 is a broad-host-range rhizobial strain that establishes symbiotic interactions with legumes and tolerates different environmental stresses such as heat, acidity, or salinity. This rhizobial strain produces a wide variety of symbiotically active nodulation factors (NF) induced not only by the presence of plant-released flavonoids but also under osmotic stress conditions through the LysR-type transcriptional regulators NodD1 (flavonoids) and NodD2 (osmotic stress). However, the activation of NodD2 under high-osmotic-stress conditions remains elusive. Here, we have studied the role of a new AraC-type regulator (named as OnfD) in the symbiotic interaction of R. tropici CIAT 899 with Phaseolus vulgaris and Lotus plants. We determined that OnfD is required under salt stress conditions for the transcriptional activation of the nodulation genes and therefore the synthesis and export of NF, which are required for a successful symbiosis with P. vulgaris. Moreover, using bacterial two-hybrid analysis, we demonstrated that the OnfD and NodD2 proteins form homodimers and OnfD/NodD2 form heterodimers, which could be involved in the production of NF in the presence of osmotic stress conditions since both regulators are required for NF synthesis in the presence of salt. A structural model of OnfD is presented and discussed. IMPORTANCE The synthesis and export of rhizobial NF are mediated by a conserved group of LysR-type regulators, the NodD proteins. Here, we have demonstrated that a non-LysR-type regulator, an AraC-type protein, is required for the transcriptional activation of symbiotic genes and for the synthesis of symbiotically active NF under salt stress conditions.
|Funding agencies||Ministerio de Economía y Competitividad (MINECO). España|
|Project ID.||project AGL2016-77163-R|
|Citation||Cerro Sánchez, P.d., Ayala García, P., Buzón García, P., Castells Graells, R., López Baena, F.J., Ollero Márquez, F.J. y Pérez Montaño, F.d.A. (2020). OnfD, an AraC-Type Transcriptional Regulator Encoded by Rhizobium tropici CIAT 899 and Involved in Nod Factor Synthesis and Symbiosis. Applied and Environmental Microbiology, 86 (19), e01297-1320.|