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Abstract Symbiotic nitrogen (N) fixation entails successful interaction between legume hosts and rhizobia that occur in specialized organs called nodules. N-fixing legumes have a higher demand for phosphorus (P) than legumes grown on mineral N. Medicago truncatula is an important model plant for characterization of effects of P deficiency at the molecular level. Hence, a study was carried out to address the alteration in metabolite levels of M. truncatula grown aeroponically and subjected to 4 weeks of P stress. First, GC-MS-based untargeted metabolomics initially revealed changes in the metabolic profile of nodules, with increased levels of amino acids and sugars and a decline in amounts of organic acids. Subsequently, LC-MS/MS was used to quantify these compounds including phosphorylated metabolites in the whole plant. Our results showed a drastic reduction in levels of organic acids and phosphorylated compounds in –P leaves, with a moderate reduction in –P roots and nodules. Additionally, sugars and amino acids were elevated in the whole plant under P deprivation. These findings provide evidence that N fixation in M. truncatula is mediated through a N feedback mechanism that in parallel is related to carbon and P metabolism.
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Metabolomic profiling of wild‐type and mutant soybean root nodules using laser‐ablation electrospray ionization mass spectrometry reveals altered metabolism
SUMMARY The establishment of the nitrogen‐fixing symbiosis between soybean andBradyrhizobium japonicumis a complex process. To document the changes in plant metabolism as a result of symbiosis, we utilized laser ablation electrospray ionization‐mass spectrometry (LAESI‐MS) forin situmetabolic profiling of wild‐type nodules, nodules infected with aB. japonicum nifHmutant unable to fix nitrogen, nodules doubly infected by both strains, and nodules formed on plants mutated in thestearoyl‐acyl carrier protein desaturase(sacpd‐c) gene, which were previously shown to have an altered nodule ultrastructure. The results showed that the relative abundance of fatty acids, purines, and lipids was significantly changed in response to the symbiosis. ThenifHmutant nodules had elevated levels of jasmonic acid, correlating with signs of nitrogen deprivation. Nodules resulting from the mixed inoculant displayed similar, overlapping metabolic distributions within the sectors of effective (fix+) and ineffective (nifHmutant, fix−) endosymbionts. These data are inconsistent with the notion that plant sanctioning is cell autonomous. Nodules lackingsacpd‐cdisplayed an elevation of soyasaponins and organic acids in the central necrotic regions. The present study demonstrates the utility of LAESI‐MS for high‐throughput screening of plant phenotypes. Overall, nodules disrupted in the symbiosis were elevated in metabolites related to plant defense.
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- Award ID(s):
- 1734145
- PAR ID:
- 10456896
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 103
- Issue:
- 5
- ISSN:
- 0960-7412
- Page Range / eLocation ID:
- p. 1937-1958
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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