A MYB coiled‐coil transcription factor interacts with NSP 2 and is involved in nodulation in L otus japonicus

Summary Transcription factor complex formation is a central step in regulating gene expression. In this report, a novel MYB coiled‐coil transcription factor referred to as IPN 2, for I nteracting P rotein of NSP 2, is described. The interaction between IPN 2 and NSP 2 was examined by protein pull‐down assays and bimolecular fluorescence complementation ( B i FC ). Subcellular localization of proteins, gene expression and gene function were assessed in transgenic hairy roots expressing tagged recombinant proteins, promoter‐reporter and RNA interference ( RNA i) constructs, respectively. The GRAS domain of NSP 2 and the coiled‐coil domain of IPN 2 were found to be responsible for the interaction between the two proteins. IPN 2 had strong transcription activation activity, bound directly to the NIN gene promoter, and was localized to the nuclei of Lotus japonicus root cells. The expression of IPN 2 was elevated during nodule development, coinciding with increased NSP 2 gene expression during nodule organogenesis. RNA i‐mediated knockdown expression of IPN 2 did not affect arbuscular mycorrhizal development, but had deleterious effects on rhizobial infection and nodule formation in L . japonicus . These results demonstrate an important role of IPN 2 in nodule organogenesis and place a new MYB transcription factor in the N od signaling pathway.