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.

中文翻译：

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OnfD，一种由热带根瘤菌CIAT 899编码的AraC型转录调节子，参与Nod因子的合成和共生。

热带根瘤菌CIAT 899是一种广泛宿主的根瘤菌菌株，可与豆类建立共生相互作用，并能耐受不同的环境胁迫，例如热量，酸度或盐度。该根瘤菌菌株产生多种共生活性结瘤因子（NF），不仅由植物释放的类黄酮的存在引起，而且在渗透胁迫条件下通过LysR型转录调节剂NodD1（类黄酮）和NodD2（渗透胁迫）诱导。但是，在高渗透压条件下激活NodD2仍然难以捉摸。在这里，我们研究了一种新型AraC型调节剂（命名为OnfD）在tropic。CIAT 899与菜豆和莲花的共生相互作用中的作用。植物。我们确定OnfD在盐胁迫条件下对于结节基因的转录激活以及因此NF的合成和输出是必需的，而NF是成功与寻常型共生共生所必需的。此外，使用细菌二杂交分析，我们证明OnfD和NodD2蛋白形成同型二聚体，而OnfD / NodD2蛋白形成异二聚体，这在渗透胁迫条件下可能与NF的产生有关，因为这两种调节剂都是NF合成所需的在盐的存在下。提出并讨论了OnfD的结构模型。