Glycerolipid transfer for the building of membranes in plant cells.

Membranes of plant organelles have specific glycerolipid compositions. Selective distribution of lipids at the levels of subcellular organelles, membrane leaflets and membrane domains reflects a complex and finely tuned lipid homeostasis. Glycerolipid neosynthesis occurs mainly in plastid envelope and endoplasmic reticulum membranes. Since most lipids are not only present in the membranes where they are synthesized, one cannot explain membrane specific lipid distribution by metabolic processes confined in each membrane compartment. In this review, we present our current understanding of glycerolipid trafficking in plant cells. We examine the potential mechanisms involved in lipid transport inside bilayers and from one membrane to another. We survey lipid transfers going through vesicular membrane flow and those dependent on lipid transfer proteins at membrane contact sites. By introducing recently described membrane lipid reorganization during phosphate deprivation and recent developments issued from mutant analyses, we detail the specific lipid transfers towards or outwards the chloroplast envelope

Lipid Trafficking at Membrane Contact Sites During Plant Development and Stress Response

The biogenesis of cellular membranes involves an important traffic of lipids from their site of synthesis to their final destination. Lipid transfer can be mediated by vesicular or non-vesicular pathways. The non-vesicular pathway requires the close apposition of two membranes to form a functional platform, called membrane contact sites (MCSs), where lipids are exchanged. These last decades, MCSs have been observed between virtually all organelles and a role in lipid transfer has been demonstrated for some of them. In plants, the lipid composition of membranes is highly dynamic and can be drastically modified in response to environmental changes. This highlights the importance of understanding the mechanisms involved in the regulation of membrane lipid homeostasis in plants. This review summarizes our current knowledge about the non-vesicular transport of lipids at MCSs in plants and its regulation during stress

Editorial: Structure and Function of Chloroplasts

The primary energy resource of life on earth is the sun, whose energy is captured in the form of usable carbons by a process called photosynthesis. Photosynthesis occurs within a cellular organelle adapted to that purpose, called the chloroplast. Chloroplasts are unique metabolic and sensory organelles restricted to plants, algae, and a few protists. In this special topic, we aimed to gather new research, hypotheses, and reviews that would help us to better understand the important role of chloroplasts in all photosynthetic organisms. We were fortunate enough to have submissions from many talented chloroplast researchers. This topic contains a total of 24 papers of which 13 are original research, 3 are methods, 5 are reviews or mini-reviews, 2 are perspectives and one is a hypothesis

Phosphate deprivation induces transfer of DGDG galactolipid from chloroplast to mitochondria

In many soils plants have to grow in a shortage of phosphate, leading to development of phosphate-saving mechanisms. At the cellular level, these mechanisms include conversion of phospholipids into glycolipids, mainly digalactosyldiacylglycerol (DGDG). The lipid changes are not restricted to plastid membranes where DGDG is synthesized and resides under normal conditions. In plant cells deprived of phosphate, mitochondria contain a high concentration of DGDG, whereas mitochondria have no glycolipids in control cells. Mitochondria do not synthesize this pool of DGDG, which structure is shown to be characteristic of a DGD type enzyme present in plastid envelope. The transfer of DGDG between plastid and mitochondria is investigated and detected between mitochondria-closely associated envelope vesicles and mitochondria. This transfer does not apparently involve the endomembrane system and would rather be dependent upon contacts between plastids and mitochondria. Contacts sites are favored at early stages of phosphate deprivation when DGDG cell content is just starting to respond to phosphate deprivation

Importance of the hexagonal lipid phase in biological membrane organization

Domains are present in every natural membrane. They are characterized by a distinctive protein and/or lipid composition. Their size is highly variable from the nano- to the micrometer scale. The domains confer specific properties to the membrane leading to original structure and function. The determinants leading to domain organization are therefore important but remain obscure. This review presents how the ability of lipids to organize into hexagonal II or lamellar phases can promote particular local structures within membranes. Since biological membranes are composed of a mixture of lipids, each with distinctive biophysical properties, lateral and transversal sorting of lipids can promote creation of domains inside the membrane through local modulation of the lipid phase. Lipid biophysical properties have been characterized for long based on in vitro analyses using non-natural lipid molecules; their re-examinations using natural lipids might open interesting perspectives on membrane architecture occurring in vivo in various cellular and physiological contexts

ETUDE DES REMANIEMENTS LIPIDIQUES DES CELLULES VEGETALES EN CARENCE DE PHOSPHATE

Phosphate is often a limiting factor for plant growth in soil. In plant cell, phosphate deprivation induces a decrease of phospholipid amount, mobilizing phosphate present in theses molecules. This decrease is compensated by an increase of non phosphorous plastidic glycolipid amount such as digalactosyldiacylglycerol (DGDG). We have shown that under phosphate deprivation a part of phospholipids is transformed into phosphatidylcholine (PC), producing a transitory increase of PC in short time of deprivation. Then, PC is hydrolyzed into diacylglycerol (DAG) that increases and feeds DGDG synthesis. Our results suggest a direct transfer of DAG from non plastidic membranes to plastid envelope, where DGDG synthesis is located. Then, newly synthesized DGDG is exported to extraplastidic membranes. We have shown that DGDG is present in mitochondria and is transferred from plastids to mitochondria by contact between specialized plastid envelope domains and mitochondria outer membrane. Finally, in order to identify proteins involved in lipid remodeling, we collaborated to a transcriptomic analysis of Arabidopsis thaliana genome under phosphate deprivation. We have selected from this analysis a phospholipase D, PLDzéta2, that is likely involved in intracellular amount of inorganic phosphate and in PC hydrolysis for DAG feeding of galactolipid synthesis.Dans de nombreux sols, le phosphate est un élément limitant pour la croissance des plantes. Au niveau cellulaire, la carence de phosphate induit une diminution de la teneur en phospholipides, permettant la mobilisation du phosphate contenu dans ces molécules. Cette baisse est compensée par une augmentation de la teneur en glycolipides plastidiaux non phosphorés tels que le digalactosyldiacylglycérol (DGDG). Nous avons montré qu'au cours de la carence de phosphate, une partie des phospholipides est reconvertie en phosphatidylcholine (PC), produisant, au temps court de carence, une accumulation transitoire de PC dans les cellules. La PC est ensuite hydrolysée en diacylglycérol (DAG) qui s'accumule en carence de phosphate et nourrit la synthèse du DGDG. Nos résultats suggèrent un transfert direct du DAG à partir des membranes non plastidiales vers l'enveloppe des plastes, lieu de synthèse du DGDG. Le DGDG est ensuite exporté dans des membranes extraplastidiales. Nous avons mis en évidence la présence de DGDG dans les mitochondries et son transfert des plastes vers les mitochondries à partir de contacts entre des domaines spécialisés de l'enveloppe des plastes et des mitochondries. Enfin, pour identifier des protéines impliquées dans ces mécanismes de remaniement des lipides, nous avons collaboré à une analyse transcriptomique du génome d'Arabidopsis thaliana en carence de phosphate. Nous avons notamment sélectionné une phospholipase D, PLDzéta2, qui semble impliquée dans le contrôle de la teneur intracellulaire en phosphate inorganique et dans l'hydrolyse de la PC pour l'approvisionnement en DAG de la synthèse des galactolipides

Etude des remaniements lipidiques des cellules végétales en carence de phosphate

Dans de nombreux sols, le phosphate est un élément limitant pour la croissance des plantes. Au niveau cellulaire, la carence de phosphate induit une diminution de la teneur en phospholipides, permettant la mobilisation du phosphate contenu dans ces molécules. Cette baisse est compensée par une augmentation de la teneur en glycolipides plastidiaux non phosphorés tels que le digalactosyldiacylglycérol (DGDG). Nous avons montré qu'au cours de la carence de phosphate, une partie des phospholipides est reconvertie en phosphatidylcholine (PC), produisant, au temps court de carence, une accumulation transitoire de PC dans les cellules. La PC est ensuite hydrolysée en diacylglycérol (DAG) qui s'accumule en carence de phosphate et nourrit la synthèse du DGDG. Nos résultats suggèrent un transfert direct du DAG à partir des membranes non plastidiales vers l'enveloppe des plastes, lieu de synthèse du DGDG. Le DGDG est ensuite exporté dans des membranes extraplastidiales. Nous avons mis en évidence la présence de DGDG dans les mitochondries et son transfert des plastes vers les mitochondries à partir de contacts entre des domaines spécialisés de l'enveloppe des plastes et des mitochondries. Enfin, pour identifier des protéines impliquées dans ces mécanismes de remaniement des lipides, nous avons collaboré à une analyse transcriptomique du génome d'Arabidopsis thaliana en carence de phosphate. Nous avons notamment sélectionné une phospholipase D, PLDzéta2, qui semble impliquée dans le contrôle de la teneur intracellulaire en phosphate inorganique et dans l'hydrolyse de la PC pour l'approvisionnement en DAG de la synthèse des galactolipides.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Editorial: Structure and Function of Chloroplasts

The primary energy resource of life on earth is the sun, whose energy is captured in the form of usable carbons by a process called photosynthesis. Photosynthesis occurs within a cellular organelle adapted to that purpose, called the chloroplast. Chloroplasts are unique metabolic and sensory organelles restricted to plants, algae, and a few protists. In this special topic, we aimed to gather new research, hypotheses, and reviews that would help us to better understand the important role of chloroplasts in all photosynthetic organisms. We were fortunate enough to have submissions from many talented chloroplast researchers. This topic contains a total of 24 papers of which 13 are original research, 3 are methods, 5 are reviews or mini-reviews, 2 are perspectives and one is a hypothesis