Identification and Molecular Characterization of RWP-RK Transcription Factors in Soybean.

The is a small family of plant-specific transcription factors that are mainly involved in nitrate starvation responses, gametogenesis, and root nodulation. To date, the molecular mechanisms underpinning nitrate-regulated gene expression in many plant species have been extensively studied. However, the regulation of nodulation-specific proteins during nodulation and rhizobial infection under nitrogen starvation in soybean still remain unclear. Here, we investigated the genome-wide identification of transcription factors and their essential role in nitrate-inducible and stress-responsive gene expression in soybean. In total, 28 genes were identified from the soybean genome, which were unevenly distributed on 20 chromosomes from 5 distinct groups during phylogeny classification. The conserved topology of RWP-RK protein motifs, cis-acting elements, and functional annotation has led to their potential as key regulators during plant growth, development, and diverse stress responses. The RNA-seq data revealed that the up-regulation of genes in the nodules indicated that these genes might play crucial roles during root nodulation in soybean. Furthermore, qRT-PCR analysis revealed that most GmRWP-RK genes under infection and diverse environmental conditions (such as heat, nitrogen, and salt) were significantly induced, thus opening a new window of possibilities into their regulatory roles in adaptation mechanisms that allow soybean to tolerate biotic and abiotic stress. In addition, the dual luciferase assay indicated that and efficiently bind to the promoters of , , and , highlighting their possible involvement in nodule formation. Together, our findings provide novel insights into the functional role of the family during defense responses and root nodulation in soybean.