miR172 Regulates Nodule Number in Soybean

MicroRNAs (miRNAs) are noncoding RNAs that are master regulators of various biological processes by post-transcriptionally repressing their target genes. It has been shown that miRNAs are involved in nodulation in legumes, however, the molecular mechanism through which miR172 regulates nodulation remains elusive. Recently, we have demonstrated that miR172c is a central positive regulator of both rhizobia infection and nodule organogenesis in soybean. miR172c is induced by either compatible B. japonicum or lipo-oligosaccharide Nod Factor, and continues to be upregulated during nodule development. Alteration in miR172c results in dramatic changes in nodule initiation and nodule number. Furthermore, miR172c regulates nodule formation by repressing its target gene, Nodule Number Control 1 (GmNNC1), which encodes a protein that directly targets the promoter of the early nodulin gene, GmENOD40. Moreover, we proved that miR172c functionally depends on GmNFR1α/5α and its activity is negatively regulated by autoregulation of nodulation (AON). Thus, we elucidate a miR172c-mediated regulatory mechanism that modulates soybean nodulation and identify a node that links NF and AON signaling pathways to fine tune ultimate nodule number in soybean.