A Novel ARID DNA-Binding Protein Interacts with SymRK and Is Expressed during Early Nodule Development in Lotus japonicus

Hui Zhu,Zhongming Zhang,Zonglie Hong,Heng Kang,Tao Chen,Maosheng Zhu,Qing Fang

doi:10.1104/pp.108.119164

Abstract

During the establishment of symbiosis in legume roots, the rhizobial Nod factor signal is perceived by the host cells via receptor-like kinases, including SymRK. The NODULE INCEPTION (NIN) gene in Lotus japonicus is required for rhizobial entry into root cells and for nodule organogenesis. We describe here a novel DNA-binding protein from L. japonicus, referred to as SIP1, because it was identified as a SymRK-interacting protein. SIP1 contains a conserved AT-rich interaction domain (ARID) and represents a unique member of the ARID-containing proteins in plants. The C terminus of SIP1 was found to be responsible for its interaction with the kinase domain of SymRK and for homodimerization in the absence of DNA. SIP1 specifically binds to the promoter of LjNIN but not to that of LjCBP1 (a calcium-binding protein gene), both of which are known to be inducible by Nod factors. SIP1 recognizes two of the three AT-rich domains present in the NIN gene promoter. Deletion of one of the AT-rich domains at the NIN promoter diminishes the binding of SIP1 to the NIN promoter. The protein is localized to the nuclei when expressed as a red fluorescence fusion protein in the onion (Allium cepa) epidermal cells. The SIP1 gene is expressed constitutively in the uninfected roots, and its expression levels are elevated after infection by Mesorhizobium loti. It is proposed that SIP1 may be required for the expression of NIN and involved in the initial communications between the rhizobia and the host root cells.

Highlights

During the establishment of symbiosis in legume roots, the rhizobial Nod factor signal is perceived by the host cells via receptorlike kinases, including SymRK
In an attempt to identify SymRK-associated proteins, we used the kinase domain of SymRK as a bait of the yeast two-hybrid system and screened a Lotus cDNA library constructed in the prey vector pGADT7-Rec2
SymRK is a member of a large family of Leu-rich repeat (LRR) receptor-like kinases (RLKs) in plants and is required for the legume root cells to

Summary

Introduction

During the establishment of symbiosis in legume roots, the rhizobial Nod factor signal is perceived by the host cells via receptorlike kinases, including SymRK. It is proposed that SIP1 may be required for the expression of NIN and involved in the initial communications between the rhizobia and the host root cells. The binding of NodD to these flavonoids activates the protein and promotes the transcription of other nod genes involved in the synthesis and secretion of Nod factors, the rhizobial signaling molecules (Peck et al, 2006). Rhizobial Nod factors have been shown to be recognized by lysin motif (LysM)-containing receptor-like kinases (RLKs), such as NFR1/NFR5 from Lotus japonicus and LYK3 and NFP from Medicago truncatula (Madsen et al, 2003; Radutoiu et al, 2003; Limpens et al, 2003; Arrighi et al, 2006). A NORKinteracting partner in M. truncatula has been identified as 3-hydroxy-3-methylglutaryl-CoA reductase 1, which may link the Nod signaling pathway with the formation of isoprenoid-derived phytohormones (Kevei et al, 2007)

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Conclusion