Medicago truncatula NIN Is Essential for Rhizobial-Independent Nodule Organogenesis Induced by Autoactive Calcium/Calmodulin-Dependent Protein Kinase

Abstract

The symbiotic association between legumes and nitrogen-fixing bacteria collectively known as rhizobia results in the formation of a unique plant root organ called the nodule. This process is initiated following the perception of rhizobial nodulation factors by the host plant. Nod factor (NF)-stimulated plant responses, including nodulation-specific gene expression, is mediated by the NF signaling pathway. Plant mutants in this pathway are unable to nodulate. We describe here the cloning and characterization of two mutant alleles of the Medicago truncatula ortholog of the Lotus japonicus and pea (Pisum sativum) NIN gene. The Mtnin mutants undergo excessive root hair curling but are impaired in infection and fail to form nodules following inoculation with Sinorhizobium meliloti. Our investigation of early NF-induced gene expression using the reporter fusion ENOD11TGUS in the Mtnin-1 mutant demonstrates that MtNIN is not essential for early NF signaling but may negatively regulate the spatial pattern of ENOD11 expression. It was recently shown that an autoactive form of a nodulation-specific calcium/calmodulin-dependent protein kinase is sufficient to induce nodule organogenesis in the absence of rhizobia. We show here that MtNIN is essential for autoactive calcium/calmodulin-dependent protein kinase-induced nodule organogenesis. The non-nodulating hcl mutant has a similar phenotype to Mtnin, but we demonstrate that HCL is not required in this process. Based on our data, we suggest that MtNIN functions downstream of the early NF signaling pathway to coordinate and regulate the correct temporal and spatial formation of root nodules.

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

“…Mtnin mutants are particularly interesting because they have early signalling responses to Nod factor but are impaired in both induction of cortical cell division and infection thread development, suggesting that MtNIN might be involved in integrating these processes 61 (TABLE 1). This is consistent with a model in which cortical cell divisions provide a signal for the initiation and maintenance of infection threads.…”

Deep Sequencing of the Medicago truncatula Root Transcriptome Reveals a Massive and Early Interaction between Nodulation Factor and Ethylene Signals

“…4A). Their rapid up-regulation reflects their importance in effecting subsequent symbiotic gene expression and their absolute requirement for nodulation (Kaló et al, 2005;Andriankaja et al, 2007;Marsh et al, 2007). Groups G1, G2, and G3 contained an additional 20 TFs that are coinduced along with NIN, ERN1, and NSP2 by 3 hpi (Fig.…”

CLE Peptides Control Medicago truncatula Nodulation Locally and Systemically

“…Medicago truncatula 'Jemalong A17' and 'J5' as well as nin, bit1-1, nsp1, nsp2, dmi1, dmi2, dmi3, and sunn-1 mutants (Catoira et al, 2000;Oldroyd and Long, 2003;Marsh et al, 2007;Middleton et al, 2007) and pENOD11:GUS transgenic seeds (Journet et al, 2001) were grown and inoculated as described (Mergaert et al, 2003). Sinorhizobium meliloti 1021, Sm1021 pHC60-GFP (Cheng and Walker, 1998), Sm1021 pQE81-dsRedT3 (Bevis and Glick, 2002), Sm2011 pBHRmRFP (Smit et al, 2005), Sm2011 pHC60-GFP (Cheng and Walker, 1998), and Sm2011 pMH682-Gmi6390 (Roche et al, 1991) were grown at 28°C in yeast extract broth medium (Vervliet et al, 1975) supplemented with 10 mg L 21 tetracycline for the Sm1021 pHC60-GFP, Sm1021 pQE81-dsRedT3, Sm2011 pBHR-mRFP, Sm2011 pHC60-GFP, and Sm1021 pMH682-Gmi6390 strains.…”

“…This signaling cascade triggers Ca 2+ spiking in and around the nucleus. Decoding of this Ca 2+ signature by a Ca 2+ calmodulin-binding protein (DMI3) results in the activation of the transcription factors Nodulation Signaling Pathway1 (NSP1), NSP2, Ethylene-Responsive Binding Domain Factor Required for Nodulation1 (ERN1), and Nodule Inception (NIN; Schauser et al, 1999;Catoira et al, 2000;Borisov et al, 2003;Oldroyd and Long, 2003;Gleason et al, 2006;Andriankaja et al, 2007;Marsh et al, 2007;Middleton et al, 2007;Oldroyd and Downie, 2008). NSP2, ERN1, and NIN also play a role downstream of the cytokinin signaling to trigger cortical cell division (Tirichine et al, 2007;Frugier et al, 2008).…”