Soybean miR172c Targets the Repressive AP2 Transcription Factor NNC1 to Activate ENOD40 Expression and Regulate Nodule Initiation  

Abstract

MicroRNAs are noncoding RNAs that act as master regulators to modulate various biological processes by posttranscriptionally repressing their target genes. Repression of their target mRNA(s) can modulate signaling cascades and subsequent cellular events. Recently, a role for miR172 in soybean (Glycine max) nodulation has been described; however, the molecular mechanism through which miR172 acts to regulate nodulation has yet to be explored. Here, we demonstrate that soybean miR172c modulates both rhizobium infection and nodule organogenesis. miR172c was induced in soybean roots inoculated with either compatible Bradyrhizobium japonicum or lipooligosaccharide Nod factor and was highly upregulated during nodule development. Reduced activity and overexpression of miR172c caused dramatic changes in nodule initiation and nodule number. We show that soybean miR172c regulates nodule formation by repressing its target gene, Nodule Number Control1, which encodes a protein that directly targets the promoter of the early nodulin gene, ENOD40. Interestingly, transcriptional levels of miR172c were regulated by both Nod Factor Receptor1α/5α-mediated activation and by autoregulation of nodulation-mediated inhibition. Thus, we established a direct link between miR172c and the Nod factor signaling pathway in addition to adding a new layer to the precise nodulation regulation mechanism of soybean.

Phosphorylation-Dependent Regulation of G-Protein Cycle during Nodule Formation in Soybean

“…Root segments 3 cm below the root-hypocotyl junction were cut and harvested at 4 and 6 dpi, respectively. Roots were fixed with ethanol:glacial acetic acid (3:1) for 2 h and stained with 0.01% methylene blue for 15 min (Wang et al, 2014b). The stained transgenic roots were observed by light microscopy to detect the deformed root hairs and nodule primordia in three different biological replicates each with n = 10 to 12 roots.…”

The Micro-RNA172c-APETALA2-1 Node as a Key Regulator of the Common Bean-Rhizobium etli Nitrogen Fixation Symbiosis

“…In legumes, conserved roles of the miR172 node have been documented for L. japonicus (control of flowering time; Yamashino et al, 2013) and soybean (control of juvenile-to-adult phase transition; Yoshikawa et al, 2013). In addition, the control of nodulation during the rhizobia symbiosis has been proposed as a family-specific acquired function of miR172 in different legumes and has been demonstrated for soybean (Yan et al, 2013;Wang et al, 2014). In this work, we identified the miR172 node as a relevant regulator of rhizobial infection and nodulation in common bean.…”

“…The differential expression of miR172 isoforms in plant organs/tissues at different developmental stages has been reported for Arabidopsis and soybean (Aukerman and Sakai, 2003;Wu et al, 2009;Yan et al, 2013;Wang et al, 2014). In this work, we performed expression analyses of the miR172 isoforms and their putative AP2 target genes ( Fig.…”

“…They propose that AP2, directly or indirectly, controls the expression of nonsymbiotic hemoglobin, which is essential for regulating the levels of nodulation and nitrogenase activity (Yan et al, 2013). Very recently, Wang et al (2014) demonstrated that soybean miR172c modulates rhizobial infection and nodule organogenesis. They showed that miR172c regulates nodule formation by repressing its target gene NODULE NUMBER CONTROL1 (NNC1), an AP2 TF, which directly targets and represses the early nodulin gene ENOD40 that plays a key role in nodulation.…”

MicroRNA167-Directed Regulation of the Auxin Response Factors GmARF8a and GmARF8b Is Required for Soybean Nodulation and Lateral Root Development

“…Several profiling studies have revealed that miRNAs are involved in rhizobial infection, nodule formation, and nodule functioning (Subramanian et al, 2008;Lelandais-Brière et al, 2009;Wang et al, 2009;Bazin et al, 2012;De Luis et al, 2012;Dong et al, 2013; for review, see Formey et al, 2014). Indeed, functional analyses have demonstrated an altered number of nodules following miRNA overexpression or knockdown (Combier et al, 2006;Li et al, 2010;De Luis et al, 2012;Turner et al, 2013;Yan et al, 2013;Wang et al, 2014). A recent study reported that ectopic expression of miR160, which negatively regulates AUXIN RESPONSE FACTOR10 (ARF10), increased auxin sensitivity and inhibited nodule development.…”