The Effect of Exogenous Nitrate on LCO Signalling, Cytokinin Accumulation, and Nodule Initiation in Medicago truncatula

ABSTRACTLegumes form a mutualistic endosymbiosis with nitrogen-fixing rhizobia. These rhizobia are housed intracellularly in specialised lateral root organs, called nodules. Initiation of these nodules is triggered by bacterial derived signalling molecules, lipochitooligosaccharides (LCO). The process of nitrogen fixation is highly energy-demanding and therefore nodule initiation is tightly regulated. Nitrate is a potent inhibitor of nodulation. However, the precise mechanisms by which nitrate inhibits nodulation is poorly understood. Here, we demonstrate that in Medicago truncatula nitrate interferes with the transcriptional regulation of the ethylene biosynthesis gene ACC SYNTHASE 10. ACSs commit the rate limiting step in ethylene biosynthesis and in M. truncatula ACS10 is highly expressed in the zone of the root where nodulation occurs. Our results show that a reduction in ACS10 expression in response to LCO exposure correlates with the ability to form nodules. In addition, RNAi-mediated knockdown of ACS10 confers nodulation ability under otherwise inhibitory nitrate conditions. This discovery sheds new light on how ethylene is involved in the inhibition of nodulation by nitrate, bringing us one step closer to understanding how plants regulate their susceptibility towards rhizobia.

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Expression of the nodulation and nitrogen fixation genes in Rhizobium meliloti during development

Genome ◽

10.1139/g89-054 ◽

1989 ◽

Vol 31 (1) ◽

pp. 354-360 ◽

Cited By ~ 2

Author(s):

San Chiun Shen ◽

Shui Ping Wang ◽

Guan Qiao Yu ◽

Jia Bi Zhu

Keyword(s):

Nitrogen Fixation ◽

Rhizobium Meliloti ◽

Abnormal Development ◽

Wild Type ◽

Free Living ◽

Nod Genes ◽

Nodule Initiation ◽

Fix Genes ◽

Nitrogen Fixation Genes

Genes that specify nodulation (nod genes) are only active in the free-living rhizobia or in the nodule initiation state of rhizobia. As soon as the repression of nod genes occurs in the bacteroids of the nodule, nifA is induced, while ntrC is inactivated and thus the nifA-mediated nif/fix genes are turned on. Limitation of available oxygen brings about the induction of nifA, which reflects the actual status of nif/fix gene activities in symbiotic state of rhizobia. Oxygen thus appears to be a major symbiotic signal to the expression of bacteroid nif/fix genes. Mutation of nifA or shortage of nifA product in wild-type rhizobia caused by the inhibition of multicopy nifH/fixA promoters leads to an abnormal development of nodules and premature degradation of bacteroids in nodules.Key words: nitrogen fixation, nodulation, nif/fix regulation, nifA mutant.

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Differential responses of the sunn4 and rdn1-1 super-nodulation mutants of Medicago truncatula to elevated atmospheric CO2

Annals of Botany ◽

10.1093/aob/mcab098 ◽

2021 ◽

Author(s):

Yunfa Qiao ◽

Shujie Miao ◽

Jian Jin ◽

Ulrike Mathesius ◽

Caixian Tang

Keyword(s):

Nitrogen Fixation ◽

Elevated Co2 ◽

Medicago Truncatula ◽

N2 Fixation ◽

Sink Strength ◽

Wild Type ◽

Total N ◽

Autoregulation Of Nodulation ◽

Nodulation Mutants ◽

Fixation Capacity

Abstract Background and Aims Nitrogen fixation in legumes requires tight control of carbon and nitrogen balance. Thus, legumes control nodule numbers via an autoregulation mechanism. ‘Autoregulation of nodulation’ mutants super-nodulate and are thought to be carbon-limited due to the high carbon-sink strength of excessive nodules. This study aimed to examine the effect of increasing carbon supply on the performance of super-nodulation mutants. Methods We compared the responses of Medicago truncatula super-nodulation mutants (sunn-4 and rdn1-1) and wild type to five CO2 levels (300-850 μmol mol -1). Nodule formation and N2 fixation were assessed in soil-grown plants at 18 and 42 days after sowing. Key results Shoot and root biomass, nodule number and biomass, nitrogenase activity and fixed-N per plant of all genotypes increased with increasing CO2 concentration and reached the maximum around 700 μmol mol -1. While the sunn-4 mutant showed strong growth-retardation compared to wild-type plants, elevated CO2 increased shoot biomass and total N content of rdn1-1 mutant up to two-fold. This was accompanied by a four-fold increase in nitrogen fixation capacity in the rdn1-1 mutant. Conclusions These results suggest that the super-nodulation phenotype per se did not limit growth. The additional nitrogen fixation capacity of the rdn1-1 mutant may enhance the benefit of elevated CO2 on plant growth and N2 fixation.

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Ethylene inhibits stem trichome formation in Arabidopsis

10.7287/peerj.preprints.27047 ◽

2018 ◽

Author(s):

Susan I Gibson

Keyword(s):

Arabidopsis Thaliana ◽

Substantial Reduction ◽

Ethylene Biosynthesis ◽

Model Systems ◽

Wild Type ◽

Normal Numbers ◽

Biosynthesis Inhibitor ◽

Ethylene Response ◽

Normal Differentiation ◽

Ethylene Insensitivity

Trichomes, specialized cells that form on the above ground parts of plants, are useful model systems for studying cell differentiation. In this study, the plant hormone ethylene was found to strongly inhibit formation of trichomes on stems of Arabidopsis thaliana. Plants grown in the presence of high concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid fail to form trichomes on their primary inflorescences. In addition, plants carrying mutations in CTR1 that confer a constitutive response to ethylene exhibit severe reductions in stem trichome numbers. In contrast, plants carrying mutations that confer ethylene insensitivity, and plants grown in the presence of an ethylene biosynthesis inhibitor, produce normal numbers of stem trichomes. Together, these results suggest that either excess ethylene or a constitutive ethylene response prevents the normal differentiation of cells that would otherwise form stem trichomes. Reduced ethylene levels and decreased ethylene response, in constrast, appear insufficient to cause cells that do not normally form trichomes to form trichomes. In contrast to ethylene, application of exogenous Glc results in increased stem trichome numbers. Besides affecting stem trichome numbers, ethylene may also affect branching of stem trichomes. In Arabidopsis thaliana, the vast majority of stem trichomes are unbranched. When wild-type Arabidiopsis thaliana of the Col-0 ecotype are grown in the presence of an ethylene biosynthesis inhibitor, the percentage of stem trichomes that are branched increases significantly. However, growth in the presence of an ethylene biosynthesis inhibitor does not affect stem branching in wild-type Arabidopsis thaliana of the Ler-0 ecotype. Plants carrying the etr1-1 and ein2-1 mutations, which cause ethylene insensitivity, have an increased percentage of branched stem trichomes. In contrast, plants carrying the ctr1-1 and ctr1-12 mutations have a decreased percentage of branched stem trichomes. Growth in the presence of a precursor of ethylene biosynthesis also causes a substantial reduction in branching of Arabidopsis leaf trichomes, suggesting that ethylene has a negative effect on branching of both leaf and stem trichomes in Arabidopsis.

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Ethylene inhibits stem trichome formation in Arabidopsis

10.7287/peerj.preprints.27047v1 ◽

2018 ◽

Author(s):

Susan I Gibson

Keyword(s):

Arabidopsis Thaliana ◽

Substantial Reduction ◽

Ethylene Biosynthesis ◽

Model Systems ◽

Wild Type ◽

Normal Numbers ◽

Biosynthesis Inhibitor ◽

Ethylene Response ◽

Normal Differentiation ◽

Ethylene Insensitivity

Trichomes, specialized cells that form on the above ground parts of plants, are useful model systems for studying cell differentiation. In this study, the plant hormone ethylene was found to strongly inhibit formation of trichomes on stems of Arabidopsis thaliana. Plants grown in the presence of high concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid fail to form trichomes on their primary inflorescences. In addition, plants carrying mutations in CTR1 that confer a constitutive response to ethylene exhibit severe reductions in stem trichome numbers. In contrast, plants carrying mutations that confer ethylene insensitivity, and plants grown in the presence of an ethylene biosynthesis inhibitor, produce normal numbers of stem trichomes. Together, these results suggest that either excess ethylene or a constitutive ethylene response prevents the normal differentiation of cells that would otherwise form stem trichomes. Reduced ethylene levels and decreased ethylene response, in constrast, appear insufficient to cause cells that do not normally form trichomes to form trichomes. In contrast to ethylene, application of exogenous Glc results in increased stem trichome numbers. Besides affecting stem trichome numbers, ethylene may also affect branching of stem trichomes. In Arabidopsis thaliana, the vast majority of stem trichomes are unbranched. When wild-type Arabidiopsis thaliana of the Col-0 ecotype are grown in the presence of an ethylene biosynthesis inhibitor, the percentage of stem trichomes that are branched increases significantly. However, growth in the presence of an ethylene biosynthesis inhibitor does not affect stem branching in wild-type Arabidopsis thaliana of the Ler-0 ecotype. Plants carrying the etr1-1 and ein2-1 mutations, which cause ethylene insensitivity, have an increased percentage of branched stem trichomes. In contrast, plants carrying the ctr1-1 and ctr1-12 mutations have a decreased percentage of branched stem trichomes. Growth in the presence of a precursor of ethylene biosynthesis also causes a substantial reduction in branching of Arabidopsis leaf trichomes, suggesting that ethylene has a negative effect on branching of both leaf and stem trichomes in Arabidopsis.

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Faculty Opinions recommendation of Is N-feedback involved in the inhibition of nitrogen fixation in drought-stressed Medicago truncatula?

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.718000080.793474272 ◽

2013 ◽

Author(s):

John Ward ◽

Margaret Taylor

Keyword(s):

Nitrogen Fixation ◽

Medicago Truncatula

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Genetic disruption of calpain correlates with loss of membrane blebbing and differential expression of RhoGDI-1, cofilin and tropomyosin

Biochemical Journal ◽

10.1042/bj20070522 ◽

2008 ◽

Vol 411 (3) ◽

pp. 657-666 ◽

Cited By ~ 11

Author(s):

Anna K. Larsen ◽

René Lametsch ◽

John S. Elce ◽

Jørgen K. Larsen ◽

Bo Thomsen ◽

...

Keyword(s):

Membrane Surface ◽

Proteome Analysis ◽

Time Lapse ◽

Wild Type ◽

Genetic Rescue ◽

Dynamic Regulation ◽

Membrane Blebbing ◽

Signalling Molecules ◽

Membrane Blebs

Dynamic regulation of the actin cytoskeleton is important for cell motility, spreading and the formation of membrane surface extensions such as lamellipodia, ruffles and blebs. The ubiquitous calpains contribute to integrin-mediated cytoskeletal remodelling during cell migration and spreading, by cleavage of focal adhesion components and signalling molecules. In the present study, the live-cell morphology of calpain-knockout and wild-type cells was examined by time-lapse fluorescence microscopy, and a role of calpain in mediating the formation of sporadic membrane blebs was established. Membrane blebbing was significantly reduced in calpain-knockout cells, and genetic rescue fully restored the wild-type phenotype in knockout cells. Proteomic comparison of wild-type and knockout cells identified decreased levels of RhoGDI-1 (Rho GDP-dissociation inhibitor) and cofilin 1, and increased levels of tropomyosin in calpain-knockout cells, suggesting a role of calpain in regulating membrane extensions involving these proteins. RhoGDI, cofilin and tropomyosin are known regulators of actin filament dynamics and membrane extensions. The reduced levels of RhoGDI-1 in calpain-knockout cells observed by proteome analysis were confirmed by immunoblotting. Genetic rescue of the calpain-knockout cells enhanced RhoGDI-1-expression 2-fold above that normally present in wild-type cells. These results suggest a regulatory connection between calpain and RhoGDI-1 in promoting formation of membrane blebs.

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Effect of plant age and sowing density on nitrogen fixation of Medicago truncatula at 2 different dates of sowing

Agronomie ◽

10.1051/agro:19930803 ◽

1993 ◽

Vol 13 (8) ◽

pp. 699-709

Author(s):

ABK Dahmane ◽

RD Graham

Keyword(s):

Nitrogen Fixation ◽

Medicago Truncatula ◽

Plant Age

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Regulation and characterization of mutants of fixABCX in Rhizobium leguminosarum.

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-02-21-0037-r ◽

2021 ◽

Author(s):

Isabel Webb ◽

Jiabao Xu ◽

Carmen Sanchez-Cañizares ◽

Ramakrishnan Karunakaran ◽

Vinoy Ramachandran ◽

...

Keyword(s):

Nitrogen Fixation ◽

Rhizobium Leguminosarum ◽

Redox Balance ◽

Rna Seq ◽

Wild Type ◽

Transcription Start Sites ◽

Sym Plasmid ◽

Microaerobic Conditions ◽

Type Infection

Symbiosis between Rhizobium leguminosarum and Pisum sativum requires tight control of redox balance in order to maintain respiration under the microaerobic conditions required for nitrogenase, whilst still producing the eight electrons and sixteen molecules of ATP needed for nitrogen fixation. FixABCX, electron transfer flavoproteins essential for nitrogen fixation, are encoded on the Sym plasmid (pRL10), immediately upstream of nifA, which encodes the general transcriptional regulator of nitrogen fixation. There is a symbiotically-regulated NifA-dependent promoter upstream of fixA (PnifA1), as well as an additional basal constitutive promoter driving background expression of nifA (PnifA2). These were confirmed by 5’-end mapping of transcription start sites using differential (d) RNA-seq. Complementation of polar fixAB and fixX mutants (Fix- strains) confirmed expression of nifA from PnifA1 in symbiosis. Electron microscopy combined with single-cell Raman microspectroscopy characterization of fixAB mutants revealed previously unknown heterogeneity in bacteroid morphology within a single nodule. Two morphotypes of mutant fixAB bacteroids were observed. One was larger than wild-type bacteroids and contained high levels of polyhydroxy-3-butyrate, a complex energy/reductant storage product. A second bacteroid phenotype was morphologically and compositionally different and resembled wild-type infection thread cells. From these two characteristic fixAB mutant bacteroid morphotypes, inferences can be drawn on the metabolism of wild-type nitrogen-fixing bacteroids.

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