Béatrice Satiat-Jeunemaitre

French National Centre for Scientific Research | CNRS · Institut des Sciences Végétales (ISV)

Ion transporters are key players of cellular processes. The mechanistic properties of ion transporters have been well elucidated by biophysical methods. Meanwhile, the understanding of their exact functions in cellular homeostasis is limited by the difficulty of monitoring their activity in vivo. The development of biosensors to track subtle change...

Ion transporters are key players of cellular processes. The mechanistic properties of ion transporters have been well elucidated by biophysical methods. Meanwhile the understanding of their exact functions in the whole cell homeostasis is limited by the difficulty to monitor their activity in vivo . The development of biosensors to track subtle cha...

Autophagy is a eukaryotic catabolic pathway essential for growth and development. In plants, it is activated in response to environmental cues or developmental stimuli. However, in contrast to other eukaryotic systems, we know relatively little regarding the molecular players involved in autophagy and the regulation of this complex pathway. In the...

Autophagy is a catabolic process used by eukaryotic cells to maintain or restore cellular and organismal homeostasis. A better understanding of autophagy in plant biology could lead to an improvement of the recycling processes of plant cells and thus contribute, for example, towards reducing the negative ecological consequences of nitrogen-based fe...

DNA remodelling during endoreplication appears to be a strong developmental characteristic in orchids. In this study, we analysed DNA content and nuclei in 41 species of orchids to further map the genome evolution in this plant family. We demonstrate that the DNA remodelling observed in 36 out of 41 orchids studied corresponds to strict partial end...

Recently, a number of diverse correlative light and electron microscopy (CLEM) protocols have been developed for several model organisms. However, these CLEM methods have largely bypassed plant cell research, with most protocols having little application to plants. Using autophagosome identification as a biological background, we propose and compar...

While there is an explosion in Correlative Electron and Light Microscopy (CLEM) protocols, many have been developed on different eukaryotic models, though reports on plant cell exploration by CLEM remain scarce (Bell et al., 2013). Indeed, plant cells represent a challenge for imaging in many ways. Plant specificities have to be taken into account...

Brassinosteroids are plant steroid hormones that control many aspects of plant growth and development, and are perceived at the cell surface by the plasma membrane-localized receptor kinase BRI1. Here we show that BRI1 is post-translationally modified by K63 polyubiquitin chains in vivo. Using both artificial ubiquitination of BRI1 and generation o...

Imaging or quantifying protein synthesis in cellulo through a well-resolved analysis of the cell cycle (also defining G1 subcompartments) is a methodological challenge. Click chemistry is the method of choice to reveal the thymidine analogue 5-ethynyl-2′-deoxyuridine (EdU) and track proliferating nuclei undergoing DNA synthesis. However, the click...

Autophagosomes arise in yeast and animals from the sealing of a cup-shaped double-membrane precursor, the phagophore. The concerted action of about 30 evolutionarily conserved autophagy related (ATG) proteins lies at the core of this process. However, the mechanisms allowing phagophore generation and its differentiation into a sealed autophagosome...

Autophagosomes are the organelles responsible for macroautophagy and arise, in yeast and animals, from the sealing of a cup-shaped double-membrane precursor, the phagophore. How the phagophore is generated and grows into a sealed autophagosome is still not clear in detail, and unknown in plants. This is due, in part, to the scarcity of structurally...

The formation of the autophagic vesicles requires the recruitment of ubiquitin-like Atg8 proteins to the membrane of nascent autophagosomes. Seven Atg8 homologs are present in mammals, split into the LC3 and the GABARAP/GATE-16 families, whose respective functions are unknown. Using Caenorhabditis elegans, we investigated the functions of the GABAR...

Cardiolipin (CL) is the signature phospholipid of the mitochondrial inner membrane. In animals and yeast (Saccharomyces cerevisiae), CL depletion affects the stability of respiratory supercomplexes and is thus crucial to the energy metabolism of obligate aerobes. In eukaryotes, the last step of CL synthesis is catalyzed by CARDIOLIPIN SYNTHASE (CLS...

Several vacuolar sorting determinants (VSDs) have been described for protein trafficking to the vacuoles in plant cells. Due to the variety in plant models, cell types and experimental approaches used to decipher vacuolar targeting processes, it is not clear whether the well-known three groups of VSDs identified so far exhaust all the targeting mec...

N-terminal fatty acylations (N-myristoylation [MYR] and S-palmitoylation [PAL]) are crucial modifications affecting 2 to 4% of eukaryotic proteins. The role of these modifications is to target proteins to membranes. Predictive tools have revealed unexpected targets of these acylations in Arabidopsis thaliana and other plants. However, little is kno...

Optimizing sample processing, reducing the duration of the preparation of specimen, and adjusting procedures to adhere to new health and safety regulations, are the current challenges of plant electron microscopists. To address these issues, plant processing protocols for TEM, combining the use of polyphenolic compounds as substitute for uranyl ace...

Plant cells are characterized by the presence of chloroplasts, membrane lipids of which contain up to ∼80% mono- and digalactosyldiacylglycerol (MGDG and DGDG). The synthesis of MGDG in the chloroplast envelope is essential for the biogenesis and function of photosynthetic membranes, is coordinated with lipid metabolism in other cell compartments a...

Acyl chain length is thought to be crucial for biophysical properties of the membrane, in particular during cell division, when active vesicular fusion is necessary. In higher plants, the process of cytokinesis is unique, because the separation of the two daughter cells is carried out by de novo vesicular fusion to generate a laterally expanding ce...

Sphingolipids are a class of structural membrane lipids involved in membrane trafficking and cell polarity. Functional analysis of the ceramide synthase family in Arabidopsis thaliana demonstrates the existence of two activities selective for the length of the acyl chains. Very-long-acyl-chain (C > 18 carbons) but not long-chain sphingolipids are e...

Plant cell vacuoles are diverse and dynamic structures. In particular, during seed germination, the protein storage vacuoles are rapidly replaced by a central lytic vacuole enabling rapid elongation of embryo cells. In this study, we investigate the dynamic remodeling of vacuolar compartments during Arabidopsis seed germination using immunocytochem...

Sphingolipids play an essential role in the functioning of the secretory pathway in eukaryotic organisms. Their importance in the functional organization of plant cells has not been studied in any detail before. The sphingolipid synthesis inhibitor fumonisin B1 (FB1), a mycotoxin acting as a specific inhibitor of ceramide synthase, was tested for i...

TRACKING GENE EXPRESSION AND PRODUCTS IN CELLS AND TISSUES. Reporter genes; glucuronidase staining; Bioluminescent reporter genes; Tracking mRNA; In situ hybridisation; Probe Accessibility; Choice of nucleic acid probe; Tracking mRNA in live plant cells; Tracking protein expression: affinity labelling and immunocytochemistry. Constraints of plant c...

In this chapter we shall deal with the technical aspect of cellular bio-imaging, including fluorochromes, but leaving the important theme of genetically-coded probes for the complementary chapter 14 (Bolte et al., 2007). To appreciate many of the innovations raised in this chapter, we must stress that “The image of a point taken with a microscope i...

Photoactivatable and photoconvertible fluorescent proteins capable of pronounced light-induced spectral changes are a powerful addition to the fluorescent protein toolbox of the cell biologist. They permit specific tracking of one subcellular structure (organelle or cell subdomain) within a differentially labelled population. They also enable pulse...

Plants use a variety of small peptides for cell to cell communication during growth and development. Leguminous plants are characterized by their ability to develop nitrogen-fixing nodules via an interaction with symbiotic bacteria. During nodule organogenesis, several so-called nodulin genes are induced, including large families that encode small...

Legume plants host nitrogen-fixing endosymbiotic Rhizobium bacteria in root nodules. In Medicago truncatula, the bacteria undergo an irreversible (terminal) differentiation mediated by hitherto unidentified plant factors. We demonstrated that these factors are nodule-specific cysteine-rich (NCR) peptides that are targeted to the bacteria and enter...

Le cycle dans le contexte du développement. Régulation de la prolifération : une machinerie moléculaire de base commune aux eucaryotes. La biologie cellulaire de la prolifération : spécificités de la cellule végétale. Prolifération cellulaire et Cycle des organites intracellulaires : un dialogue fonctionnel. Durée d’un cycle cellulaire : de quelque...

Remorins (REMs) are proteins of unknown function specific to vascular plants. We have used imaging and biochemical approaches and in situ labeling to demonstrate that REM clusters at plasmodesmata and in approximately 70-nm membrane domains, similar to lipid rafts, in the cytosolic leaflet of the plasma membrane. From a manipulation of REM levels i...

The organization and dynamics of the plant endomembrane system require both universal and plant-specific molecules and compartments. The latter, despite the growing wealth of information, remains poorly understood. From the study of an Arabidopsis thaliana male gametophytic mutant, it was possible to isolate a gene named POKY POLLEN TUBE (POK) esse...

As compared with other eukaryotic cells, plants have developed an endoplasmic reticulum (ER)–Golgi interface with very specific structural characteristics. ER to Golgi and Golgi to ER transport appear not to be dependent on the cytoskeleton, and ER export sites have been found closely associated with Golgi bodies to constitute entire mobile units....

The plant Golgi apparatus has an important role in protein glycosylation and sorting, but is also a major biosynthetic organelle that synthesises large quantities of cell wall polysaccharides. This is reflected in the organisation of the Golgi apparatus as numerous individual stacks of cisternae that are dispersed through the cell. Each stack is po...

The PIN-FORMED (PIN) proteins are plasma-membrane-associated facilitators of auxin transport. They are often targeted to one side of the cell only through subcellular mechanisms that remain largely unknown. Here, we have studied the potential roles of the cytoskeleton and endomembrane system in the localisation of PIN proteins. Immunocytochemistry...

Whilst plant cells are apparently equipped with all the necessary molecular machinery for receptor-mediated endocytosis, the physiological role of this process in these cells remains an enigma. In this article, we consider current opinions of endocytosis in plants and define some of the problems that have impeded progress in our under-standing of t...

The synthesis of cellulose microfibrils requires the presence of a membrane-bound endo-1,4-beta-D-glucanase, KORRIGAN1 (KOR1). Although the exact biochemical role of KOR1 in cellulose synthesis is unknown, we used the protein as a marker to explore the potential involvement of subcellular transport processes in cellulose synthesis. Using immunofluo...

The plant Golgi apparatus is composed of many separate stacks of cisternae which are often associated with the endoplasmic reticulum and which in many cell types are motile. In this review, we discuss the latest data on the molecular regulation of Golgi function. The concept of the Golgi as a distinct organelle is challenged and the possibility of...

A careful scrutiny of the dynamics of secretory compartments in the entire eukaryotic world reveals many common themes. The most fundamental theme is that the Golgi apparatus and related structures appear as compartments formed by the act of transporting cargo. The second common theme is the pivotal importance for endomembrane dynamics of shifting...

Parallèlement à l'identification de nombreux gènes dans des organismes modèles. la biologie contemporaine s'enrichit de moyens remarquables pour une exploration fonctionnelle de la cellule. Elle bénéficie d'une forte amélioration de la résolution spatiale et temporelle pour l'observation de structures biologiques. Citons entre autres l'essor de la...

Vacuolar H+-ATPases are large protein complexes of more than 700 kDa that acidify endomembrane compartments and are part of the secretory system of eukaryotic cells. They are built from 14 different (VHA)-subunits. The paper addresses the question of sub-cellular localisation and subunit composition of plant V-ATPase in vivo and in vitro mainly by...

FM-dyes are widely used to study endocytosis, vesicle trafficking and organelle organization in living eukaryotic cells. The increasing use of FM-dyes in plant cells has provoked much debate with regard to their suitability as endocytosis markers, which organelles they stain and the precise pathways they follow through the vesicle trafficking netwo...

We report on the sub-cellular localisation and function of m-Rab(mc), a N-myristoylated plant-specific Rab-GTPase previously characterised at the molecular level and also by structural analysis in Mesembryanthemum crystallinum. By confocal laser scanning microscopy, we identified m-Rab(mc) predominantly on the prevacuolar compartment of the lytic v...

This paper examines the molecular machinery involved in membrane exchange within the plant endomembrane system. A study has been undertaken on beta-COP-like proteins in plant cells using M3A5, an antibody raised against the conserved sequence of mammalian beta-COP proteins. In mammalian cells, beta-COP proteins are part of a complex named the coato...

It is not easy to understand how the electron microscopes and electron microscope techniques that we know today developed from the primitive ideas of the first microscopists of the 1930s. Newcomers to the subject in particular, their time almost fully occupied with grasping practical methods and modern computing techniques, can rarely devote much a...

Effects of brefeldin A (BFA) and nordihydroguaiaretic acid (NDGA) on endomembrane structures and lipid synthesis were compared in maize root cells and tobacco Bright Yellow-2 cells. Immunofluorescence and electron microscopy studies showed that NDGA altered the structure and distribution of the endoplasmic reticulum (ER) within 1 h but not of the G...

Auxin is a major growth hormone in plants and the first plant hormone to be discovered and studied. Active research over >60 years has shed light on many of the molecular mechanisms of its action including transport, perception, signal transduction, and a variety of biosynthetic pathways in various species, tissues, and developmental stages. The co...

Mechanisms regulating plant host differentiation of the nitrogen-fixing root nodules remain mostly unknown. Sinorhizobium meliloti induces this process in Medicago sativa in which the Mszpt2-1 gene is expressed in vascular bundles of roots and nodules. This gene codes for a Krüppel-like zinc finger protein, a class of transcription factors involved...

We recently demonstrated the presence of a new asparagine-linked complex glycan on plant glycoproteins that harbors the Lewis a (Lea), or Galbeta(1-3)[Fucalpha(1-4)]GlcNAc, epitope, which in mammalian cells plays an important role in cell-to-cell recognition. Here we show that the monoclonal antibody JIM 84, which is widely used as a Golgi marker i...

Small GTP-binding Rho proteins are involved in signalling, cell polarity, membrane outgrowths and actin stabilization in eukaryotes. Known plant homologues represent essentially the Rac subfamily and an original Rop (Rho in pollen). Mammalian Rho proteins are preferential targets of clostridial toxins. In alfalfa (Medicago sativa L.) cells, Clostri...

The parameters of Brefeldin A (BFA) action in plant cells have been further investigated in maize root tips. Incubation of maize root tip cells with 100 µg ml−1 BFA for 2 h induces the vesiculation and aggregation of Golgi membrane to form BFA compartments; an effect that is reversed by incubation of the cells in BFA-free medium. In this paper, the...

Eukaryotic cells are characterised by the organised distribution of membrane bounded compartments in their cytoplasm. The endoplasmic reticulum (ER) and the Golgi apparatus (GA) are part of this endomembrane machinery. They are involved in protein flow, and are in charge of specific functions such as the assembly, sorting and transport of newly syn...

Leek (Allium porrum) plasma membrane is enriched in phosphatidylserine (PS) by the vesicular pathway, in a way similar to that already observed in animal cells (B. Sturbois-Balcerzak, D.J. Morre, O. Loreau, J.P. Noel, P. Moreau, C. Cassagne [1995] Plant Physiol Biochem 33: 625-637). In this paper we document the formation of PS-rich small vesicles...