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

Abstract

During the establishment of symbiosis in legume roots, the rhizobial Nod factor signal is perceived by the host cells via receptorlike 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.

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

“…Additional proteins involved in actin rearrangement and protein degradation, as well as hormone perception and signaling, are also involved in nodule development. Proteins of the nuclear pore complex (NENA), an ankyrin protein Vapyrin, an ARID domaincontaining protein (SIP1), and HMGR1, have been shown to act in conjunction with CCaMK and have a role in nodule formation in Lotus japonicus and Medicago truncatula (Kevei et al, 2007;Zhu et al, 2008;Groth et al, 2010;Hayashi et al, 2010;Murray et al, 2011).…”

A Ubiquitin Ligase of Symbiosis Receptor Kinase Involved in Nodule Organogenesis

“…Reducing the level of HMGR1 by inhibitor lavastatin or RNA interference (RNAi) expression results in a drastic decrease in nodulation in M. truncatula (Kevei et al, 2007). SIP1 binds the promoter of the NIN (for nodule inception) gene (Zhu et al, 2008), which is required for rhizobial recognition, IT formation, and nodule primordial initiation (Schauser et al, 1999). These results suggest that SymRK may form protein complex with key regulatory proteins of downstream cellular responses.…”

“…In search of interacting proteins of SymRK, we took the two-hybrid approach and screened an L. japonicus complementary DNA (cDNA) library constructed in a yeast (Saccharomyces cerevisiae) expression vector (Zhu et al, 2008). Several positive clones were isolated and shown to contain cDNA inserts representing the same gene.…”

“…Screening of interaction clones was performed as described previously (Zhu et al, 2008). A total of 10 7 transformants were screened for protein-protein interaction on synthetic defined medium SD/-Leu-Trp-His-Ade.…”

“…A recent report has identified a mutation in the Gly-AspPro-Cys motif of the SymRK extracellular region that blocks the IT formation in root hairs (Kosuta et al, 2011). Previously, the SymRK kinase domain has been shown to interact with 3-hydroxy-3-methylglutaryl CoA reductase1 (HMGR1) from M. truncatula (Kevei et al, 2007), and an ARID-type DNA-binding protein (Zhu et al, 2008). HMGR1 catalyzes the formation of mevalonic acid and is the rate-limiting step of the mevalonic acid pathway, which is required for production of specific isoprenoid compounds such as cytokinins, phytosteroids, and isoprenoid-modified signal proteins.…”