Biology subjects

Le Hir, R.

Publications and source records attributed to Le Hir, R..

7 recordsLinked to original sources

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↗

bioRxiv2025

Too much sugar makes plants "pregnant": maternal sucrose signals fertilization in Arabidopsis seeds

Reproduction is deemed successful if it ensures the perpetuation of the species. Nonetheless, evolution has optimized reproductive efficiency across a diverse range of strategies. Animal vivipary, the process in which embryos develop inside the parents body, allows for larger offspring and better protection. This reproductive strategy relies on a fertilization signal sent to the maternal tissues to establish an embryo-supportive environment, a process known as "maternal recognition of pregnancy". Despite being a strictly animal-only term, plants independently evolved a conceptually similar strategy: the seed habit, wherein the embryo is nourished and protected by surrounding maternal tissues. We discovered that sucrose is sufficient to trigger a fertilization-independent response in the maternal tissues of Arabidopsis ovules. Upon fertilization, the release of Polycomb-mediated repression promotes the symplastic and apoplastic flow of sucrose into the seed by modulating auxin and trehalose 6-phosphate signaling. The sucrose signal is then perceived by the TARGET OF RAPAMYCIN kinase and transduced into a gibberellin response to initiate the differentiation of the seed maternal tissues. This work revealed a zygotic-maternal interplay of hormonal and sugar signaling that drives the plant "maternal recognition of fertilization", incorporating energetic cues into developmental pathways.

plant biology↗

bioRxiv2024

SUC2 sucrose transporter is required for leaf apoplasmic sucrose levels. Consequences for phloem loading strategies

Summary * The SUC/SUT sucrose transporters belong to a family of active H+/sucrose symporters, with a role of SUC2 in active apoplasmic phloem loading to drive long-distance phloem transport of sucrose in Arabidopsis. However, the cooperation with the symplasmic pathway for phloem loading remains unclear. * In this study, we explored the consequences of reducing either apoplasmic or symplasmic pathways of phloem loading. We compared a series of lines with modified expression of SUC2 gene, and we analyzed the effects on plant growth, sugar accumulation in source and sink organs, phloem transport, and gene expression. * Our data revealed that a modified expression of SUC2 impacted apoplasmic sucrose levels in source leaves but did not impact phloem transport, as might be expected, while increasing foliar storage of carbohydrates. This response differed from lines in which symplasmic communications between phloem cells was disrupted by the over-expression of a plasmodesmata-associated protein, NHL26. * Altogether, our studies indicate an unexpected effect of SUC2 for apoplasmic sucrose levels in source leaves, together with SUC1, and suggest a feedback regulation on foliar storage. This data sheds new light on the interplay between symplasmic and apoplasmic pathways for sugar loading and the consequences on leaf water flows. Summary statementThe mechanisms that coordinate apoplasmic and symplasmic loading pathways, and their effects on foliar carbon storage, remain largely unexplored. Surprisingly, the sucrose transporter SUC2 plays a significant role in maintaining sucrose levels in the apoplasm, shedding light on how apoplasmic sugar levels and water flows can interact for phloem loading.

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↗

bioRxiv2020

Hexose fluxes, mediated by vacuolar SWEET transporters, are important for xylem development in the inflorescence stem of Arabidopsis thaliana.

In higher plants, the development of the vascular system is controlled by a complex network of transcription factors. However, how nutrient availability in the vascular cells affects their development remains to be addressed. At the cellular level, cytosolic sugar availability is regulated mainly by sugar exchanges at the tonoplast through active and/or facilitated transport. In Arabidopsis thaliana, among the tonoplastic transporters, SWEET16 and SWEET17 genes have been previously localized in the vascular system. Here, using a reverse genetic approach, we propose that sugar exchanges at the tonoplast, regulated by SWEET16, are important for xylem cell division as revealed in particular by the decreased number of xylem cells in the swt16 mutant and the expression of SWEET16 at the procambium-xylem boundary. In addition, we demonstrate that transport of hexoses mediated by SWEET16 and/or SWEET17 is required to sustain the formation of the xylem secondary cell wall. This result is in line with a defect in the xylem cell wall composition as measured by FTIR in the swt16swt17 double mutant and by upregulation of several genes involved in secondary cell wall synthesis. Our work therefore supports a model in which xylem development is partially dependent on the exchange of hexoses at the tonoplast of xylem-forming cells.

plant biology↗

bioRxiv2019

Molecular framework for TIR1/AFB-Aux/IAA-dependent auxin sensing controlling adventitious rooting in Arabidopsis

In Arabidopsis thaliana, canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR (ARF) family, most of which interact with 29 auxin/indole acetic acid (Aux/IAA) repressors, themselves forming, in the presence of auxin, coreceptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLING F-BOX PROTEINS (TIR1/AFB). Different combinations of co-receptors drive specific sensing outputs, allowing auxin to control a myriad of processes. Considerable efforts have been made to discern the temporal and spatial specificity of auxin action. However, owing to a lack of obvious phenotype in single loss-of-function mutants in Aux/IAA genes, most genetic studies have relied on gain-of-function mutants, which are highly pleiotropic. In this article, we describe a molecular framework for the role of several members of the auxin sensing machinery. Using loss-of-function mutants, we demonstrate that TIR1 and AFB2 are positive regulators, whereas IAA6, IAA9 and IAA17 are negative regulators of adventitious root (AR) formation. The three Aux/IAA proteins interact with ARF6 and/or ARF8, which we have previously shown to be positive regulators of AR formation upstream of jasmonate, and likely repress their activity. Our data also suggest a dual role for TIR1 in the control of JA biosynthesis and conjugation, as revealed by upregulation of several JA biosynthesis genes in the tir1-1 mutant. In conclusion, we propose that in the presence of auxin, TIR1 and AFB2 form specific sensing complexes with IAA6, IAA9 and/or IAA17 that modulate JA homeostasis to control AR initiation.\n\nSignificanceAdventitious root (AR) formation is a quantitative trait with high phenotypic plasticity and auxin plays a major role in its control. In previous studies, we have shown that, in Arabidopsis hypocotyls, AR formation is negatively regulated by jasmonate, whose homeostasis is controlled by a regulatory module composed of three AUXIN RESPONSE FACTORS (ARF), two of which are positive regulators of three auxin inducible Gretchen Hagen3 (GH3) genes. The present work demonstrates that the two F-box proteins, i.e., TIR1 and AFB2, together with at least three Aux/IAA proteins are likely to interact in a combinatorial manner to control the activity of the two activator ARFs upstream of JA biosynthesis and/or homeostasis, thereby controlling AR initiation in Arabidopsis hypocotyls.

plant biology↗

bioRxiv2018

Synchrotron FTIR and Raman spectroscopy provide unique spectral fingerprints for Arabidopsis floral stem vascular tissues

Cell walls are highly complex structures that are modified during plant growth and development. For example, the development of phloem and xylem vascular cells, which participate in the transport of sugars and water as well as support, can be influenced by cell-specific cell wall composition. Here, we used synchrotron radiation-based infrared (SR-FTIR) and Raman spectroscopy to analyze the cell wall composition of wild-type and double mutant sweet11-1sweet12-1, which impairs sugar transport, Arabidopsis floral stem vascular tissue. The SR-FTIR spectra showed that in addition to modified xylem cell wall composition, phloem cell walls in the double mutant line were characterized by modified hemicellulose composition. Moreover, combining Raman spectroscopy with a Classification and Regression Tree (CART) method identified combinations of Raman shifts that could distinguish xylem vessels and fibers. Additionally, the disruption of SWEET11 and SWEET12 genes impacts xylem cell wall composition in a cell-specific manner, with changes in hemicelluloses and cellulose observed at the xylem vessel interface. These results suggest that the facilitated transport of sugars by transporters that exist between vascular parenchyma cells and conducting cells is important to ensuring correct phloem and xylem cell wall composition.\n\nHighlightCombining vibrational spectroscopy techniques and multivariate analysis shows that the disruption of SWEET genes impacts phloem cell wall composition and that the effect on xylem cell wall composition is cell-specific.

plant biology↗