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Abstract Legumes acquire fixed nitrogen (N) from the soil and through endosymbiotic association with diazotrophic bacteria. However, establishing and maintaining N2-fixing nodules are expensive for the host plant, relative to taking up N from the soil. Therefore, plants suppress symbiosis when N is plentiful and enhance symbiosis when N is sparse. Here, we show that the nitrate transporter MtNRT2.1 is required for optimal nodule establishment in Medicago truncatula under low-nitrate conditions and the repression of nodulation under high-nitrate conditions. The NIN-like protein (NLP) MtNLP1 is required for MtNRT2.1 expression and regulation of nitrate uptake/transport under low- and high-nitrate conditions. Under low nitrate, the gene encoding the C-terminally encoded peptide (CEP) MtCEP1 was more highly expressed, and the exogenous application of MtCEP1 systemically promoted MtNRT2.1 expression in a compact root architecture 2 (MtCRA2)-dependent manner. The enhancement of nodulation by MtCEP1 and nitrate uptake were both impaired in the Mtnrt2.1 mutant under low nitrate. Our study demonstrates that nitrate uptake by MtNRT2.1 differentially affects nodulation at low- and high-nitrate conditions through the actions of MtCEP1 and MtNLP1.
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The root hairless mutant buzz in Brachypodium distachyon shows increased nitrate uptake and signaling but does not affect overall nitrogen use efficiency
SUMMARY Root systems are uniquely adapted to fluctuations in external nutrient availability. In response to suboptimal nitrogen conditions, plants adopt a root foraging strategy that favors a deeper and more branched root architecture, enabling them to explore and acquire soil resources. This response is gradually suppressed as nitrogen conditions improve. However, the root hairless mutantbuzzinBrachypodium distachyonshows a constitutive nitrogen‐foraging phenotype with increased root growth and root branching under nitrate‐rich conditions. To investigate how this unique root structure and root hair morphology in thebuzzmutant affects nitrate metabolism, we measured the expression of nitrate‐responsive genes, nitrate uptake and accumulation, nitrate reductase activity, and nitrogen use efficiency. We found that nitrate responses were upregulated by low nitrate conditions inbuzzrelative to wild type and correlated with increased expression of nitrate transport genes. In addition,buzzmutants showed increased nitrate uptake and a higher accumulation of nitrate in shoots. Thebuzzmutant also showed increased nitrate reductase activity in the shoots under low nitrate conditions. However, developmentally mature wild‐type andbuzzplants grown under low nitrate had similar nitrogen use efficiencies. These findings suggest thatBUZZinfluences nitrate signaling and that enhanced responsiveness to nitrate is required inbuzzseedlings to compensate for the lack of root hairs. These data question the importance of root hairs in enhancing nitrate uptake and expand our understanding of how root hairs in grasses affect physiological responses to low nitrate availability.
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- Award ID(s):
- 1840761
- PAR ID:
- 10561147
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 120
- Issue:
- 6
- ISSN:
- 0960-7412
- Format(s):
- Medium: X Size: p. 2738-2751
- Size(s):
- p. 2738-2751
- Sponsoring Org:
- National Science Foundation
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