Immunogold Localisation of Glutamine Synthetase in Medicago truncatula Root Nodules

Glutamine synthetase (GS) is a vital enzyme for the assimilation of ammonia into amino acids in higher plants. In legumes, GS plays a crucial role in the assimilation of the ammonium released by nitrogen-fixing bacteria in root nodules, constituting an important metabolic knob controlling the nitrogen (N) assimilatory pathways. To identify new regulators of nodule metabolism, we profiled the transcriptome of Medicago truncatula nodules impaired in N assimilation by specifically inhibiting GS activity using phosphinothricin (PPT). Global transcript expression of nodules collected before and after PPT addition (4, 8, and 24 h) was assessed using Affymetrix M. truncatula GeneChip arrays. Hundreds of genes were regulated at the three time points, illustrating the dramatic alterations in cell metabolism that are imposed on the nodules upon GS inhibition. The data indicate that GS inhibition triggers a fast plant defense response, induces premature nodule senescence, and promotes loss of root nodule identity. Consecutive metabolic changes were identified at the three time points analyzed. The results point to a fast repression of asparagine synthesis and of the glycolytic pathway and to the synthesis of glutamate via reactions alternative to the GS/GOGAT cycle. Several genes potentially involved in the molecular surveillance for internal organic N availability are identified and a number of transporters potentially important for nodule functioning are pinpointed. The data provided by this study contributes to the mapping of regulatory and metabolic networks involved in root nodule functioning and highlight candidate modulators for functional analysis.

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Glutamine Synthetase Is a Molecular Target of Nitric Oxide in Root Nodules of Medicago truncatula and Is Regulated by Tyrosine Nitration

PLANT PHYSIOLOGY ◽

10.1104/pp.111.186056 ◽

2011 ◽

Vol 157 (3) ◽

pp. 1505-1517 ◽

Cited By ~ 84

Author(s):

Paula M. Melo ◽

Liliana S. Silva ◽

Isa Ribeiro ◽

Ana R. Seabra ◽

Helena G. Carvalho

Keyword(s):

Nitric Oxide ◽

Glutamine Synthetase ◽

Medicago Truncatula ◽

Root Nodules ◽

Molecular Target ◽

Tyrosine Nitration

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Comparison of nodule endophyte composition, diversity, and gene content between Medicago truncatula genotypes

Phytobiomes Journal ◽

10.1094/pbiomes-10-20-0077-r ◽

2021 ◽

Author(s):

Mannix Burns ◽

Brendan Epstein ◽

Liana Burghardt

Keyword(s):

Functional Groups ◽

Medicago Truncatula ◽

Root Nodules ◽

Bacterial Endophytes ◽

Host Genotype ◽

Model Legume ◽

Symbiotic Relationships ◽

Functional Assays ◽

Altered Gene ◽

Significant Direct Effect

Leguminous plants form symbiotic relationships with rhizobia. These nitrogen-fixing bacteria live in specialized root organs called nodules. While rhizobia form the most notable host relationship within root nodules, other bacterial endophytes also inhabit these root nodules and can influence host-rhizobia interactions as well as exert effects of their own, whether beneficial or detrimental. In this study, we investigate differences in nodule communities between genotypes (A17 and R108) of a single plant species, the model legume Medicago truncatula. While diversity of endophytes in nodules was similar across hosts, both nodule endophyte composition and gene functional groups differed. In contrast to the significant direct effect of host genotype, neither the presence nor identity of a host in the previous generation (either A17 or R108) had a significant effect on the nodule endophyte diversity or composition. However, whether or not a host was present altered gene functional groups. We conclude that genetic variation within a legume host species can play an important role in the establishment of nodule microbiomes. Further studies, including GWAS and functional assays, can open the door for engineering and optimizing nodule endophyte communities that promote growth or have other beneficial qualities.

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Phoma medicaginis colonizes Medicago truncatula root nodules and affects nitrogen fixation capacity

European Journal of Plant Pathology ◽

10.1007/s10658-014-0549-8 ◽

2014 ◽

Vol 141 (2) ◽

pp. 375-383 ◽

Cited By ~ 4

Author(s):

Saif-Allah Chihaoui ◽

Naceur Djébali ◽

Moncef Mrabet ◽

Fathi Barhoumi ◽

Ridha Mhamdi ◽

...

Keyword(s):

Nitrogen Fixation ◽

Medicago Truncatula ◽

Root Nodules ◽

Phoma Medicaginis ◽

Fixation Capacity

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Heterologous Expression of Rhizobial CelC2 Cellulase Impairs Symbiotic Signaling and Nodulation in Medicago truncatula

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-11-17-0265-r ◽

2018 ◽

Vol 31 (5) ◽

pp. 568-575 ◽

Cited By ~ 5

Author(s):

Marta Robledo ◽

Esther Menéndez ◽

Jose Ignacio Jiménez-Zurdo ◽

Raúl Rivas ◽

Encarna Velázquez ◽

...

Keyword(s):

Medicago Truncatula ◽

Cell Walls ◽

Rhizobium Leguminosarum ◽

Root Nodules ◽

Root Hairs ◽

Nod Factors ◽

Model Legume ◽

Ensifer Meliloti ◽

Early Nodulin ◽

The Impact

The infection of legume plants by rhizobia is tightly regulated to ensure accurate bacterial penetration, infection, and development of functionally efficient nitrogen-fixing root nodules. Rhizobial Nod factors (NF) have key roles in the elicitation of nodulation signaling. Infection of white clover roots also involves the tightly regulated specific breakdown of the noncrystalline apex of cell walls in growing root hairs, which is mediated by Rhizobium leguminosarum bv. trifolii cellulase CelC2. Here, we have analyzed the impact of this endoglucanase on symbiotic signaling in the model legume Medicago truncatula. Ensifer meliloti constitutively expressing celC gene exhibited delayed nodulation and elicited aberrant ineffective nodules, hampering plant growth in the absence of nitrogen. Cotreatment of roots with NF and CelC2 altered Ca2+ spiking in root hairs and induction of the early nodulin gene ENOD11. Our data suggest that CelC2 alters early signaling between partners in the rhizobia-legume interaction.

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