Biology subjects

Chardon, F.

Publications and source records attributed to Chardon, F..

10 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

Linking candidate causal autoimmune variants to T cell networks using genetic and epigenetic screens in primary human T cells.

Genetic variants associated with autoimmune diseases are highly enriched within putative cis-regulatory regions of CD4+ T cells, suggesting that they alter disease risk via changes in gene regulation. However, very few genetic variants have been shown to affect T cell gene expression or function. We tested >18,000 autoimmune disease-associated variants for allele-specific expression using massively parallel reporter assays in primary human CD4+ T cells. The 545 expression-modulating variants (emVars) identified greatly enrich for likely causal variants. We provide evidence that many emVars are mediated by common upstream regulatory conduits, and that putative target genes of primary T cell emVars are highly enriched within a lymphocyte activation network. Using bulk and single-cell CRISPR-interference screens, we confirm that emVar-containing T cell cis-regulatory elements modulate both known and novel target genes that regulate T cell proliferation, providing plausible mechanisms by which these variants alter autoimmune disease risk.

genetics↗

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

MiniBAR/KIAA0355 is a dual Rac and Rab effector required for ciliogenesis

Cilia protrude from the cell surface and play critical roles in in-tracellular signaling, environmental sensing and development. Actin-dependent contractility and intracellular trafficking are both required for ciliogenesis, but little is known about how these processes are coordinated. Here, we identified a Rac1-and Rab35-binding protein with a truncated BAR domain that we named MiniBAR (aka KIAA0355/GARRE) which plays a key role in ciliogenesis. MiniBAR colocalizes with Rac1 and Rab35 at the plasma membrane and on intracellular vesicles traffick-ing to the ciliary base and exhibits remarkable fast pulses at the ciliary membrane. MiniBAR depletion leads to short cilia resulting from abnormal Rac-GTP/Rho-GTP levels, increased acto-myosin-II-dependent contractility together with defective trafficking of IFT88 and ARL13B into cilia. MiniBAR-depleted zebrafish embryos display dysfunctional short cilia and hall-marks of ciliopathies including left-right asymmetry defects. Thus, MiniBAR is a unique dual Rac and Rab effector that con-trols both actin cytoskeleton and membrane trafficking for cili-ogenesis.

cell 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

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↗

bioRxiv2021

A method to enrich and purify centromeric DNA from human cells

Centromeres are key elements for chromosome segregation. Canonical centromeres are built over long-stretches of tandem repetitive arrays. Despite being quite abundant compared to other loci, centromere sequences overall still represent only 2 to 5% of the human genome, therefore studying their genetic and epigenetic features is a major challenge. Furthermore, sequencing of centromeric regions requires high coverage to fully analyze length and sequence variations, which can be extremely costly. To bypass these issues, we have developed a technique based on selective restriction digestion and size fractionation to enrich for centromeric DNA from human cells. Combining enzymes capable of cutting at high frequency throughout the genome, except within most human centromeres, with size-selection of >20 kb fragments resulted in over 25-fold enrichment in centromeric DNA. Sequencing of the enriched fractions revealed that up to 60% of the enriched material is made of centromeric DNA. This approach has great potential for making sequencing of centromeric DNA more affordable and efficient and for single DNA molecule studies.

molecular biology↗

bioRxiv2020

TransMPRA: A framework for assaying the role of many trans-acting factors at many enhancers

Gene regulation occurs through trans-acting factors (e.g. transcription factors) acting on cis-regulatory elements (e.g. enhancers). Massively parallel reporter assays (MPRAs) functionally survey large numbers of cis-regulatory elements for regulatory potential, but do not identify the trans-acting factors that mediate any observed effects. Here we describe transMPRA -- a reporter assay that efficiently combines multiplex CRISPR-mediated perturbation and MPRAs to identify trans-acting factors that modulate the regulatory activity of specific enhancers.

genomics↗