Host plant genome overcomes the lack of a bacterial gene for symbiotic nitrogen fixation

Abstract

Homocitrate is a component of the iron-molybdenum cofactor in nitrogenase, where nitrogen fixation occurs. NifV, which encodes homocitrate synthase (HCS), has been identified from various diazotrophs but is not present in most rhizobial species that perform efficient nitrogen fixation only in symbiotic association with legumes. Here we show that the FEN1 gene of a model legume, Lotus japonicus, overcomes the lack of NifV in rhizobia for symbiotic nitrogen fixation. A Fix(-) (non-fixing) plant mutant, fen1, forms morphologically normal but ineffective nodules. The causal gene, FEN1, was shown to encode HCS by its ability to complement a HCS-defective mutant of Saccharomyces cerevisiae. Homocitrate was present abundantly in wild-type nodules but was absent from ineffective fen1 nodules. Inoculation with Mesorhizobium loti carrying FEN1 or Azotobacter vinelandii NifV rescued the defect in nitrogen-fixing activity of the fen1 nodules. Exogenous supply of homocitrate also recovered the nitrogen-fixing activity of the fen1 nodules through de novo nitrogenase synthesis in the rhizobial bacteroids. These results indicate that homocitrate derived from the host plant cells is essential for the efficient and continuing synthesis of the nitrogenase system in endosymbionts, and thus provide a molecular basis for the complementary and indispensable partnership between legumes and rhizobia in symbiotic nitrogen fixation.

The SNARE Protein SYP71 Expressed in Vascular Tissues Is Involved in Symbiotic Nitrogen Fixation in Lotus japonicus Nodules

“…While studying the Fix 2 mutants of L. japonicus, four genes were identified: SST1, IGN1, FEN1, and SEN1 (Krusell et al, 2005;Kumagai et al, 2007;Hakoyama et al, 2009;Hakoyama et al, 2012). Two further genes, encoding the EFD transcription factor and DNF1, were shown to be essential for symbiotic nitrogen fixation during the investigation of the M. truncatula Fix 2 mutants (Vernié et al, 2008;Wang et al, 2010).…”

A Medicago truncatula Tobacco Retrotransposon Insertion Mutant Collection with Defects in Nodule Development and Symbiotic Nitrogen Fixation

“…Only a few genes have been cloned that are required for nodule function rather than nodule development per se (Kevei et al, 2007;Arrighi et al, 2008;Hakoyama et al, 2009Hakoyama et al, , 2012Kiss et al, 2009;Yokota et al, 2009;Haney and Long, 2010;Lefebvre et al, 2010;Miyahara et al, 2010;Wang et al, 2010;Yendrek et al, 2010;Horváth et al, 2011;Ovchinnikova et al, 2011). Although many Fix2 and Fix+/2 mutants have been described in the literature (Benaben et al, 1995;Bright et al, 2005;Starker et al, 2006;Teillet et al, 2008;Maunoury et al, 2010), many of these come from EMS populations.…”

“…Many of these are involved in bacterial signal perception and transduction, consequent regulation of gene transcription, and induction of nodule development (Catoira et al, 2000;Endre et al, 2002;Amor et al, 2003;Limpens et al, 2003;Madsen et al, 2003;Radutoiu et al, 2003;Ané et al, 2004;Mitra et al, 2004a;Smit et al, 2005;Arrighi et al, 2006;Kanamori et al, 2006;Andriankaja et al, 2007;Marsh et al, 2007;Riely et al, 2007;Saito et al, 2007;Charpentier et al, 2008). Others are required for infection and the accommodation of rhizobia in cells of developing nodules Wang et al, 2010;Horváth et al, 2011;Murray et al, 2011), while a few are required for nodule metabolism Hakoyama et al, 2009Hakoyama et al, , 2012Yendrek et al, 2010). Another group of genes have been shown to control nodule number through either root-or shoot-derived signals by a long-distance feedback regulation mechanism called autoregulation of nodulation (Krusell et al, 2002;Nishimura et al, 2002;Schnabel et al, 2005;Murray et al, 2007;Penmetsa et al, 2008;Okamoto et al, 2009;Miyazawa et al, 2010;Mortier et al, 2010;Reid et al, 2011;Schnabel et al, 2011).…”

Perturbation of Arabidopsis Amino Acid Metabolism Causes Incompatibility with the Adapted Biotrophic Pathogen Hyaloperonospora arabidopsidis

“…Plant factors required for host colonization by symbiotic nitrogen-fixing bacteria have been identified (e.g., Hakoyama et al, 2009). Plant susceptibility determinants for biotrophic pathogen colonization have also been described but are not well understood.…”