Biology subjects

Marmagne, A.

Publications and source records attributed to Marmagne, A..

12 recordsLinked to original sources

bioRxiv2026

Redirecting vacuolar nitrate transport improves nitrogen use efficiency and seed protein content

Improving seed protein content without compromising carbon allocation or yield is a major challenge for enhancing nitrogen use efficiency. Here, we show that redirecting vacuolar nitrate transport through concurrent manipulation of tonoplast proteins controlling nitrate storage or export provides an effective lever to reprogram nitrogen allocation from leaves toward the seeds. Using Arabidopsis thaliana Ws lines disrupted for the vacuolar CLC-a nitrate importer and/or overexpressing the NRT2.7 tonoplast nitrate exporter, we show that plants combining the two modifications (35S::NRT2.7(clc-a)) integrate reduced nitrogen retention in vegetative tissues with increased nitrogen allocation to seeds. As a result, 35S::NRT2.7(clc-a) plants exhibit the strongest increase in seed protein content among all genotypes (approximately +25%) without affecting seed yield, carbon concentration, or lipid composition. Altered vacuolar nitrate fluxes in 35S::NRT2.7(clc-a) stimulate nitrate assimilation, enhance nitrate reductase activity and amino acid biosynthetic pathways, and drive coordinated reprogramming of nitrogen and carbon metabolisms. Through 15N pulse chase experiments, we confirmed that 35S::NRT2.7(clc-a) shows the highest nitrogen remobilization efficiency toward seeds. Overexpression of the barley NRT2.7 homolog HvNRT2.10 in Arabidopsis wild type and clc-a backgrounds reproduces the key features of 35S::NRT2.7 phenotype, demonstrating the conservation of NRT2.7 regulatory effects on plant metabolism across species. Together, these findings identify vacuolar nitrate transport as a promising target to modulate grain protein content in cereals through genetic strategies acting on nitrogen storage and remobilization.

plant biology↗

bioRxiv2026

OEP24.1 involved in carbon allocation is a receptor of piecemeal plastid autophagy in Arabidopsis

Macroautophagy is a conserved intracellular catabolic process in eukaryotes that participates in chloroplast degradation, through the selective breakdown of chloroplast components. Selective autophagy of membrane-bound organelles typically requires receptors that bridge organelle membranes and pre-autophagosomal structures. Here we identify OEP24.1 as a new receptor in the selective chloroplast piecemeal autophagy, supporting the degradation of stromal proteins. We found that the {beta}-barrel protein OEP24.1 is located at the outer membrane of plastid envelopes and on bodies budding off plastids into the cytosol and containing stroma proteins. OEP24.1 interacts physically with ATG8 autophagy proteins in a UIM dependent manner. OEP24.1-GFP and RFP-ATG8 colocalize with in mobile autophagosome-like puncta in the cytosol and in autophagic bodies within the vacuole. Delivery of OEP24.1 to vacuole lumen is dependent on active autophagy. OEP24.1 controls carbon allocation at the whole plant level, carbon concentrations in flowering stems and xylem composition. These phenotypes can be explained by the role of OEP24.1 in metabolite diffusion across the chloroplast envelope, and by its involvement in the facilitation of chloroplast quality control through piecemeal autophagy.

plant biology↗

bioRxiv2024

Nitrate activates a MKK3-dependent MAPK module via NLP transcription factors in Arabidopsis

Plant responses to nutrient availability are critical for plant development and yield. Nitrate, the major form of nitrogen in most soils, serves as both a nutrient and signaling molecule. Nitrate itself triggers rapid, major changes in gene expression, especially via NIN-LIKE PROTEIN (NLP) transcription factors, and stimulates protein phosphorylation. Mitogen-activated protein (MAP) kinase genes are among the early nitrate-responsive genes; however, little is known about their roles in nitrate signaling pathways. Here, we show that nitrate resupply to nitrogen-depleted Arabidopsis (Arabidopsis thaliana) plants triggers, within minutes, a MAPK cascade that requires NLP-dependent transcriptional induction of MITOGEN-ACTIVATED PROTEIN KINASE KINASE KINASE 13 (MAP3K13) and MAP3K14. Importantly, nitrate reductase-deficient mutants exhibited nitrate-induced MAPK activities comparable to those observed in wild-type plants, indicating that nitrate itself is the signal that stimulates the cascade. We show that the modified expression of MAP3K13 and MAP3K14 affects nitrate-stimulated gene expression and modulates plant responses to nitrogen availability, such as nitrate uptake and senescence. Our finding that a MAPK cascade involving MAP3K13 and MAP3K14 functions in the complex regulatory network governing responses to nitrate availability will guide future strategies to optimize plant responses to nitrogen fertilization and nitrogen use efficiency. Significance statementNitrate is an essential nutrient that also acts as a signaling molecule to regulate plant metabolism and development. We identified a specific MAPK cascade that is activated by nitrate and regulates several nitrate-dependent responses, such as senescence and nitrate transport.

plant biology↗

bioRxiv2024

A multidisciplinary on-farm survey of maize-bean intercropping shows that revival of traditionalagricultural systems requires careful consideration of partner varieties and agronomic practices.

O_LICereal-legume intercropping is a promising strategy for sustainable agroecosystems. The traditional intercropping of maize and bean is experiencing a revival in some modern agricultural settings, such as in southwestern France, where maize hybrids are intercropped with the commercialized Tarbais bean. We conducted on-farm surveys and a field assay to address the following questions: How does the cropping system impact yield, nutrient uptake, and rhizosphere bacterial assemblages? Do positive or negative interactions between maize and beans dominate in intercropping? What is the effect of intercropping on plant transcriptomics? C_LIO_LIWe recorded farming practices, conducted yield and nutrient measurements, and characterized soil bacterial assemblages to compare sole-cropped maize and beans with intercropped plants. A controlled field assay was also established to extend this comparison to plant gene expression differences. C_LIO_LIIntercropping was associated with a trend towards increased bacterial diversity. The cropping system significantly influenced agronomic traits, with frequent farm-by-cropping system interactions underscoring the critical role of farming practices. Competition dominated maize-bean intercropping, with 34 negative correlations among the 47 significant ones between maize and bean traits. This competition affected yield and nutrition, but primarily impacted beans, which produced fewer but bigger/heavier seeds. Transcriptomic results concurred with these findings, revealing no differentially expressed genes in maize but 5,070 in beans under competition. C_LIO_LIOverall, our findings suggest that beneficial interactions between the two crops are hindered under current field conditions, underscoring the importance of carefully considering partner varieties and farming practices to revive traditional agricultural systems. C_LI Societal Impact StatementCereal-legume intercropping is a promising strategy for sustainable agroecosystems that leverages the biological complementarities between plant species, reducing the need for chemical inputs while enhancing field biodiversity. Here, we focused on maize-bean intercropping, which is experiencing a revival in modern conventional agricultural settings. We found a trend towards an increased soil bacterial diversity in intercropping. However, competition between the two crops dominated and primarily impacted yield and gene expression in beans. Despite lower yield, bean seeds exhibited greater size. Our study indicates that implementing variety selection of both species and adapting farming practices is essential to fully harness the potential of intercropping.

plant biology↗

bioRxiv2024

Cell wall digestibility outperforms ear in maintaining digestibility even under severe combined water and heat stress

CONTEXT OR PROBLEMForage maize is a central pillar of dairy cow feeding in France, directly influencing milk production. Drought significantly affects both maize yield and digestibility, which are both key parameters required for hybrid registration purposes. OBJECTIVE OR RESEARCH QUESTIONResearch on maize inbred lines has revealed droughts notable effect on dry matter and cell wall digestibilities due to changes in cell wall composition, directly impacting forage quality. No such studies have been performed on forage maize hybrids however, which are the main seed type used in the agricultural sector. In this paper, we aimed to understand the impact of water and heat stress on forage maize digestibility, and to uncover the factors controlling it. METHODSWe grew a range of modern forage maize hybrids for two years under four different controlled water stress modalities. These plants were agronomically, biochemically and histologically assayed, allowing us to perform a multiscale analysis to determine the traits responsible for variations in digestibility. RESULTSBy establishing a comprehensive heat and water stress index, we classified the environmental conditions. We demonstrated that under severe stress, ear production decreases significantly, but dry matter digestibility can be maintained through increased cell wall digestibility. This boost in cell wall digestibility was due to a reduction in p-hydroxycinnamic acid content and changes in lignin distribution, while lignin content and structure remained stable. The significant impact of lignin distribution on cell wall digestibility increased with the severity of the stress, reaching an extreme threshold where biochemical parameters solely account for digestibility variations. CONCLUSION AND IMPLICATIONSTo improve maize digestibility, it will be necessary to better understand how the reduction in carbon flux under stress affects p-hydroxycinnamic acid levels without greatly impacting lignin content. Finally, our work suggests that the inclusion of moderate stress conditions in future maize breeding programs will be necessary to better adapt forage maize hybrids to climate change.

plant biology↗

bioRxiv2024

Multi-scale phenotyping of senescence-related changes in roots of rapeseed in response to nitrogen deficiency

Senescence related markers have been widely studied in leaves in many plant species. Root senescence is more difficult to characterize. The existence of two different root organs in B. napus, with a taproot that appear to be specifically dedicated to the storage and remobilization of nutrients, offered the possibility of analysing the temporality of the changes linked to aging, based on the degradation of the taproot reserves. Microscopic and biochemical analyses showed that taproot plays an important role in carbon and nitrogen storage as reflected by the large quantities of starch and proteins present at early development stages. The proteomic study associated to the description of biochemical, morphological and anatomic changes provides a comprehensive picture of the main events occurring in the taproot and in the lateral roots with aging. Master modifications as protein and cell wall degradation, amino acid catabolism versus synthesis, nucleic acid degradation are presented and senescence related markers specific or not of the root types were identified. Comparison with Arabidopsis public data facilitated the identification of markers common to root and leaf senescence. The analysis of protease changes provides a list of candidates that may play a role in nitrogen and carbohydrate remobilization from taproot to the shoot and flowering organs and that would deserve attention for further functional analyses.

plant biology↗

bioRxiv2023

BdNRT2A and BdNRT3.2 are the major components of the High-Affinity nitrate Transport System in Brachypodium distachyon

O_LIAn efficient nitrate uptake system contributes to the improvement of crop nitrogen use efficiency under low nitrogen availability. The High Affinity nitrate Transport System (HATS) in plants is active in low external nitrate and is mediated by a two-component system [high affinity transporters NRT2 associated to a partner protein NRT3 (NAR2)]. C_LIO_LIIn Brachypodium, the model plant for C3 cereals, we investigated the role of BdNRT2A and BdNRT3.2 through various experimental approaches including gene expression profiling, functional characterisation in heterologous system, intracellular localization by imaging, and reverse genetics via gene silencing. C_LIO_LIExpression of BdNRT2.A and BdNRT3.2 genes in response to nitrate availability fits with the characteristics of the HATS components. Co-expression of BdNRT2A and BdNRT3.2 is required for an effective nitrate transport in the heterologous expression system Xenopus oocytes. Functional interaction between BdNRT2A-GFP and BdNRT3.2-RFP fusion proteins has been observed at the plasma membrane in Arabidopsis protoplasts in transient expression experiments. BdNRT3.2 appeared to be necessary for the plasma membrane localization of BdNRT2A. 15Nitrate influx measurements with bdnrt2a mutants (two amiRNA mutants and one NaN3 induced mutant with a truncated NRT2A protein), confirmed that BdNRT2A is a major contributor of the HATS in Brachypodium. C_LIO_LIDirected mutagenesis in BdNRT2A of a conserved Ser residue (S461) specific to monocotyledons has been performed to mimic a non-phosphorylated S461A or a constitutively phosphorylated S461D, in order to evaluate its potential role in the BdNRT2A and BdNRT3.2 interaction leading to plasma membrane targeting. Interestingly, the phosphorylation status of S461 did not modify the interaction, suggesting on a more complex mechanism. C_LIO_LIIn conclusion, our data show that BdNRT2A and BdNRT3.2 are the main components of the nitrate HATS activity in Brachypodium (Bd21-3) and allow an optimal growth in low N conditions. C_LI

plant biology↗

bioRxiv2023

Maize (Zea mays L.) interaction with the arbuscular mycorrhizal fungus Rhizophagus irregularis allows mitigation of nitrogen deficiency stress: physiological and molecular characterization

Maize is currently the most productive cereal crop in the world (www.faostat.org). Maize can form a symbiotic relationship with the Arbuscular Mycorrhizal Fungus (AMF), Rhizophagus irregularis. In this relationship, the fungus provides the plant with additional water and mineral nutrients, while the plant supplies carbon compounds to the fungus. Little is known about the N metabolism disruption during symbiosis in both partners. To address this issue, two genetically distant maize lines were studied in terms of physiological and molecular responses to AMF inoculation by dual RNA-seq, metabolomics and phenotyping. Interestingly, the beneficial effects of the AMF were observed mainly under conditions of limited N fertilization. Under such conditions, the AMF helped maintain plant biomass production. The availability of nitrogen was found to be a crucial factor influencing all the traits studied showing that the level of N supply plays a pivotal role in determining how maize plants interact with the AMF. Despite the two maize lines showing different transcriptomic and metabolomic responses to R. irregularis, their agro-physiological traits remained similar. Both the plant and fungal transcriptomes were more significantly influenced by the level of N nutrition rather than the specific maize genotype. This suggests that N availability has a more profound impact on gene expression in both organisms than the genetic makeup of the maize plant. To understand the metabolic implications of this symbiotic relationship, we integrated transcriptomic data into our recently built multi-organ Genome-scale metabolic model (GSM) called iZMA6517. Remarkably, this modelling approach was supported by metabolomics profiling, in particular increased leaf pyrimidine levels in response to AMF inoculation under limiting N supply. Consistently, fungal genes involved in pyrimidine de novo synthesis and salvage were found to be expressed in symbiotic roots. Our work highlights nucleotide and ureides metabolism as previously unrecognized factors contributing to the symbiotic N nutrition facilitated by R. irregularis, thereby enhancing maize growth. This study demonstrates the effectiveness of integrating multi-omics approaches with mathematical modelling to uncover novel metabolic mechanisms associated with AM symbiosis, without a priori.

plant biology↗

bioRxiv2023

Autophagic activity acts as a rheostat in the control of nitrogen transfer from Arabidopsis rosette leaves to the seeds according to a principle of communicating vessels

Macroautophagy is known for long as essential for the degradation and the recycling of different macromolecules in eukaryotes. However how important is autophagy for nitrogen management at the whole plant level and for plant biomass and yield productivity in unstressed and well feed plants needed further investigation. In this study, we used both autophagy knock-out mutants and autophagy over-expressors that constitutively produce numerous autophagosomes. These mutants and over-expressors were cultivated using hydroponic system to observe and compare their phenotypes under sufficient nitrate supply, and when submitted after a while to strict nitrate starvation. The shift from nitrate sufficient condition to nitrate starvation allowed us to determine how autophagy defective or stimulated lines can use their own nitrogen resources to complete their cycle. Unexpectedly we observed that irrespective of the nitrate conditions, both mutants and over-expressors exhibited early leaf senescence phenotypes relative to wild type. While autophagy mutants exhibited strong defect for N remobilisation and seed production irrespective of nitrate condition, the better performance of autophagy-over expressors for N remobilisation and seeds production was only significant under sufficient nitrate supply, i.e. when autophagy was not naturally stimulated by nitrate limitation. Interestingly, comparisons of genotypes showed that the nitrogen pool used for seed filling originated from rosette leaves, as if rosette and seeds were used as communicating vessels independently of the stem and pod connecting organs. Altogether, results show that autophagy is a master player in nitrogen management at the whole plant level that controls yield production and leaf senescence.

physiology↗

bioRxiv2022

The Arabidopsis Target of Rapamycin (TOR) kinase regulates ammonium assimilation and glutamine metabolism

In Eukaryotes, Target of Rapamycin (TOR) is a well conserved kinase that controls cell metabolism and growth in response to nutrients and environmental factors. Nitrogen (N) is an essential element for plants and TOR functions as a crucial N and amino acid sensor in animals and yeast. However, the knowledge on the connections between TOR and the overall N metabolism and assimilation in plants is still limited. In this study, we investigate the regulation of TOR in Arabidopsis by the N source as well as the impact of TOR deficiency on N metabolism. Inhibition of TOR globally decreases ammonium uptake while triggering a massive accumulation of amino acids such as Gln, but also of polyamines. Coherently, TOR complex mutants were found to be hypersensitive to Gln. We also show that the glutamine synthetase inhibitor glufosinate abolishes Gln accumulation resulting from TOR inhibition and improves the growth of TOR complex mutants. These results suggest that a high level of Gln contributes to the reduction in plant growth resulting from TOR inhibition. Glutamine synthetase activity was reduced by TOR inhibition while the enzyme amount increased. In conclusion our findings show that the TOR pathway is intimately connected to N metabolism and that a decrease in TOR activity results in a glutamine synthetase-dependent Gln and amino acids accumulation. One sentence summaryThe conserved Target of Rapamycin (TOR) kinase is an important sensor and regulator of the nitrogen metabolism and here we show that inhibiting this kinase affects ammonium uptake and results in Gln accumulation in a glutamine synthetase-dependent manner.

plant biology↗

bioRxiv2022

Proton exchange in the nitrate vacuolar transporter AtCLCa is required for growth and nitrogen use efficiency

Nitrate is a major nutrient and osmoticum for plants. To deal with its fluctuating availability in soils, plants store it into vacuoles. AtCLCa, a 2NO3-/1H+ exchanger localized on the vacuole ensures this storage process. It belongs to the CLC family that includes exchangers and channels. A mutation in a glutamate residue conserved across CLC exchangers is likely responsible for the conversion of exchangers to channels. Here, we show that a clca mutant of this residue, E203, behaves as an anion channel in its native membrane. To investigate its physiological importance, we introduced the AtCLCaE203Apoint mutation in a clca KO mutant. We first showed that these AtCLCaE203A mutants display a growth deficit linked to water homeostasis disruption. Additionally, AtCLCaE203Aexpression is not able to complement the clca defect in nitrate accumulation and favors higher N-assimilation at the vegetative stage. Further analyses at post-flowering stages indicated that AtCLCaE203A results in an increase of N uptake allocation to seeds, leading to a higher nitrogen use efficiency compared to wild-type. Altogether, these results point out the critical function of the AtCLCa exchanger on the vacuole for plant metabolism and development.

plant biology↗

bioRxiv2022

Impairment of sugar transport in the vascular system acts on nitrogen remobilisation and nitrogen use efficiency in Arabidopsis.

The carbon (C) and nitrogen (N) metabolisms have long been known to be coupled, and this is required for adjusting nitrogen use efficiency. Despite this intricate relationship, it is still unclear how a deregulation of sugar transport impacts N allocation. Here we investigated, in Arabidopsis, the consequences of the simultaneous downregulation of the genes coding for the sugar transporters SWEET11, SWEET12, SWEET16, and SWEET17 genes on various anatomical and physiological traits ranging from the stems vascular system development, plant biomass production, seed yield, and N remobilisation and use efficiency. Our results show that intracellular sugar exchanges mediated by SWEET16 and SWEET17 proteins specifically impact the vascular development but do not play a significant role in the distribution of N. Most importantly, we showed that the double mutant swt11swt12, which is also impacted in the vascular development, displays an improved nitrogen use efficiency and nitrogen remobilisation to the seeds. In addition, a significant negative correlation between sugar and amino acids contents and the inflorescence stem radial growth exists, highlighting the complex interaction between the maintenance of C/N homeostasis and the inflorescence stem development. Our results thus deepen the link between sugar transport, C/N allocation and vascular system development. HighlightThe disruption of genes coding for SWEET11 and SWEET12 sugar transporters negatively impacts the stem development but improves the plant nitrogen use efficiency and nitrogen remobilisation to the seeds.

plant biology↗