Regulation of Resource Partitioning Coordinates Nitrogen and Rhizobia Responses and Autoregulation of Nodulation in Medicago truncatula

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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Characterisation of Medicago truncatula CLE34 and CLE35 in nodulation control

10.1101/2020.07.31.231605 ◽

2020 ◽

Author(s):

Celine Mens ◽

April H. Hastwell ◽

Huanan Su ◽

Peter M. Gresshoff ◽

Ulrike Mathesius ◽

...

Keyword(s):

Pisum Sativum ◽

Medicago Truncatula ◽

Sequence Homology ◽

Dependent Manner ◽

Legume Species ◽

Mature Peptide ◽

Cle Peptides ◽

Autoregulation Of Nodulation ◽

Cle Peptide ◽

Distinct Role

AbstractLegume plants form a symbiosis with N2-fixing soil rhizobia, resulting in new root organs called nodules that enable N2-fixation. Nodulation is a costly process that is tightly regulated by the host through Autoregulation of Nodulation (AON) and nitrate-dependent regulation of nodulation. Both pathways require legume-specific CLAVATA/ESR-related (CLE) peptides. Nitrogen-induced nodulation-suppressing CLE peptides have not previously been characterised in Medicago truncatula, with only rhizobia-induced MtCLE12 and MtCLE13 identified. Here, we report on novel peptides MtCLE34 and MtCLE35 in nodulation control pathways. The nodulation-suppressing CLE peptides of five legume species were classified into three clades based on sequence homology and phylogeny. This approached identified MtCLE34 and MtCLE35 and four new CLE peptide orthologues of Pisum sativum. Whereas MtCLE12 and MtCLE13 are induced by rhizobia, MtCLE34 and MtCLE35 respond to both rhizobia and nitrate. MtCLE34 was identified as a pseudogene lacking a functional CLE-domain. Overexpression of MtCLE12, MtCLE13 and MtCLE35 inhibits nodulation. Together, our findings indicate that MtCLE12 and MtCLE13 have a distinct role in AON, while MtCLE35 regulates nodule numbers in a rhizobia- and nitrate-dependent manner. MtCLE34 likely had a similar role to MtCLE35 but its function was lost due to a nonsense mutation resulting in the loss of the mature peptide.

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Unraveling new molecular players involved in the autoregulation of nodulation in Medicago truncatula

Journal of Experimental Botany ◽

10.1093/jxb/ery465 ◽

2019 ◽

Vol 70 (4) ◽

pp. 1407-1417 ◽

Cited By ~ 11

Author(s):

Pierre Gautrat ◽

Virginie Mortier ◽

Carole Laffont ◽

Annick De Keyser ◽

Justine Fromentin ◽

...

Keyword(s):

Medicago Truncatula ◽

Autoregulation Of Nodulation

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Multiple Autoregulation of Nodulation (AON) Signals Identified through Split Root Analysis of Medicago truncatula sunn and rdn1 Mutants

Plants ◽

10.3390/plants4020209 ◽

2015 ◽

Vol 4 (2) ◽

pp. 209-224 ◽

Cited By ~ 31

Author(s):

Tessema Kassaw ◽

William Jr. ◽

Julia Frugoli

Keyword(s):

Medicago Truncatula ◽

Split Root ◽

Autoregulation Of Nodulation ◽

Root Analysis

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Nitrate-Induced CLE Peptide Systemically Inhibits Nodulation in Medicago truncatula

Plants ◽

10.3390/plants9111456 ◽

2020 ◽

Vol 9 (11) ◽

pp. 1456

Author(s):

Maria Lebedeva ◽

Mahboobeh Azarakhsh ◽

Yaroslavna Yashenkova ◽

Lyudmila Lutova

Keyword(s):

Medicago Truncatula ◽

Lotus Japonicus ◽

Dependent Manner ◽

Receptor Kinase ◽

Nitrate Treatment ◽

Whole Plant ◽

Cle Peptides ◽

Autoregulation Of Nodulation ◽

Cle Peptide ◽

Plant Level

Legume plants form nitrogen-fixing nodules in symbiosis with soil bacteria rhizobia. The number of symbiotic nodules is controlled at the whole-plant level with autoregulation of nodulation (AON), which includes a shoot-acting CLV1-like receptor kinase and mobile CLE (CLAVATA3/ENDOSPERM SURROUNDING REGION-related) peptides that are produced in the root in response to rhizobia inoculation. In addition to rhizobia-induced CLE peptides, nitrate-induced CLE genes have been identified in Lotus japonicus and Glycine max, which inhibited nodulation when overexpressed. However, nitrate-induced CLE genes that systemically suppress nodulation in AON-dependent manner have not been identified in Medicago truncatula. Here, we found that MtCLE35 expression is activated by both rhizobia inoculation and nitrate treatment in M. truncatula, similarly to L. japonicus CLE genes. Moreover, we found that MtCLE35 systemically suppresses nodulation in AON-dependent manner, suggesting that MtCLE35 may mediate nitrate-induced inhibition of nodulation in M. truncatula.

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