Transcriptional regulation of NIN expression by IPN2 is required for root nodule symbiosis in Lotus japonicus

• Published in: The New phytologist Vol. 227; no. 2; pp. 513 - 528
• Main Authors: Xiao, Aifang, Yu, Haixiang, Fan, Yuqian, Kang, Heng, Ren, Yaping, Huang, Xiaoqin, Gao, Xiumei, Wang, Chao, Zhang, Zhongming, Zhu, Hui, Cao, Yangrong
• Format: Journal Article
• Language: English
• Published: England Wiley 01.07.2020; Wiley Subscription Services, Inc
• Subjects: Arabidopsis; DNA binding; gene expression regulation; Gene Expression Regulation, Plant; Gene regulation; Genetic analysis; Homology; Legumes; Lotus - genetics; Lotus - metabolism; Lotus japonicus; Nodulation; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Roots - genetics; Plant Roots - metabolism; Promoters; Proteins; Root development; root nodule symbiosis; Root Nodules, Plant - genetics; Root Nodules, Plant - metabolism; Signal transduction; Symbiosis; Transcription; transcription activation; Transcription factors; gene expression regulation; transcription activation; Lotus japonicus; root nodule symbiosis; DNA binding
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.16553

• Expression of Nodule Inception (NIN) is essential for initiation of legume–rhizobial symbiosis. An existing model regarding the regulation of NIN expression involves two GRAS transcription factors – NSP1 (Nodulation Signaling Pathway 1) and NSP2. NSP2 forms a complex with NSP1 to directly bind to NIN promoter. However, rhizobial treatment-induced NIN expression could still be detected in the nsp1 mutant plants, suggesting that other proteins must be involved in the regulation of NIN expression. • A combination of molecular, biochemical and genetic analyses was used to investigate the molecular basis of IPN2 in regulating root development and NIN expression in Lotus japonicus. • In this study, we identified that IPN2 is a close homolog of Arabidopsis APL (ALTERED PHLOEM DEVELOPMENT) with essential function in root development. However, Lotus IPN2 has a different expression pattern compared with the Arabidopsis APL gene. IPN2 binds to the IPN2-responsive cis element (IPN2-RE) of NIN promoter and activates NIN expression. IPN2, NSP1 and NSP2 form a protein complex to directly target NIN promoter and activate NIN expression in the legume–rhizobial symbiosis. • Our data refine the regulatory model of NIN expression that NSP2 works together with NSP1 and IPN2 to activate the NIN gene allowing nodulation in L. japonicus.