Occurrence and Biosynthesis of Alkyl Hydroxycinnamates in Plant Lipid Barriers

The plant lipid barriers cuticle and suberin represent one of the largest biological interfaces on the planet. They are comprised of an insoluble polymeric domain with associated organic solvent-soluble waxes. Suberin-associated and plant cuticular waxes contain mixtures of aliphatic components that may include alkyl hydroxycinnamates (AHCs). The canonical alkyl hydroxycinnamates are comprised of phenylpropanoids, typically coumaric, ferulic, or caffeic acids, esterified with long chain to very long chain fatty alcohols. However, many related structures are also present in the plant kingdom. Although their functions remain elusive, much progress has been made on understanding the distribution, biosynthesis, and deposition of AHCs. Herein a summary of the current state of knowledge on plant AHCs is provided

Biosynthesis and functions of very-long-chain fatty acids in the responses of plants to abiotic and biotic stresses

Very-long-chain fatty acids (i.e., fatty acids with more than 18 carbon atoms; VLCFA) are important molecules that play crucial physiological and structural roles in plants. VLCFA are specifically present in several membrane lipids and essential for membrane homeostasis. Their specific accumulation in the sphingolipids of the plasma membrane outer leaflet is of primordial importance for its correct functioning in intercellular communication. VLCFA are found in phospholipids, notably in phosphatidylserine and phosphatidylethanolamine, where they could play a role in membrane domain organization and interleaflet coupling. In epidermal cells, VLCFA are precursors of the cuticular waxes of the plant cuticle, which are of primary importance for many interactions of the plant with its surrounding environment. VLCFA are also major components of the root suberin barrier, which has been shown to be fundamental for nutrient homeostasis and plant adaptation to adverse conditions. Finally, some plants store VLCFA in the triacylglycerols of their seeds so that they later play a pivotal role in seed germination. In this review, taking advantage of the many studies conducted using Arabidopsis thaliana as a model, we present our current knowledge on the biosynthesis and regulation of VLCFA in plants, and on the various functions that VLCFA and their derivatives play in the interactions of plants with their abiotic and biotic environment

Temperature Acclimation of the Picoalga Ostreococcus tauri Triggers Early Fatty-Acid Variations and Involves a Plastidial ?3-Desaturase

Alteration of fatty-acid unsaturation is a universal response to temperature changes. Marine microalgae display the largest diversity of polyunsaturated fatty-acid (PUFA) whose content notably varies according to temperature. The physiological relevance and the molecular mechanisms underlying these changes are however, still poorly understood. The ancestral green picoalga Ostreococcus tauri displays original lipidic features that combines PUFAs from two distinctive microalgal lineages (Chlorophyceae, Chromista kingdom). In this study, optimized conditions were implemented to unveil early fatty-acid and desaturase transcriptional variations upon chilling and warming. We further functionally characterized the O. tauri ω3-desaturase which is closely related to ω3-desaturases from Chromista species. Our results show that the overall omega-3 to omega-6 ratio is swiftly and reversibly regulated by temperature variations. The proportion of the peculiar 18:5 fatty-acid and temperature are highly and inversely correlated pinpointing the importance of 18:5 temperature-dependent variations across kingdoms. Chilling rapidly and sustainably up-regulated most desaturase genes. Desaturases involved in the regulation of the C18-PUFA pool as well as the Δ5-desaturase appear to be major transcriptional targets. The only ω3-desaturase candidate, related to ω3-desaturases from Chromista species, is localized at chloroplasts in Nicotiana benthamiana and efficiently performs ω3-desaturation of C18-PUFAs in Synechocystis sp. PCC6803. Overexpression in the native host further unveils a broad impact on plastidial and non-plastidial glycerolipids illustrated by the alteration of omega-3/omega-6 ratio in C16-PUFA and VLC-PUFA pools. Global glycerolipid features of the overexpressor recall those of chilling acclimated cells.Développement d'une infrastructure française distribuée pour la métabolomique dédiée à l'innovatio

Characterization of MdMYB68, a suberin master regulator in russeted apples

IntroductionApple russeting is mainly due to the accumulation of suberin in the cell wall in response to defects and damages in the cuticle layer. Over the last decades, massive efforts have been done to better understand the complex interplay between pathways involved in the suberization process in model plants. However, the regulation mechanisms which orchestrate this complex process are still under investigation. Our previous studies highlighted a number of transcription factor candidates from the Myeloblastosis (MYB) transcription factor family which might regulate suberization in russeted or suberized apple fruit skin. Among these, we identified MdMYB68, which was co-expressed with number of well-known key suberin biosynthesis genes.MethodTo validate the MdMYB68 function, we conducted an heterologous transient expression in Nicotiana benthamiana combined with whole gene expression profiling analysis (RNA-Seq), quantification of lipids and cell wall monosaccharides, and microscopy.ResultsMdMYB68 overexpression is able to trigger the expression of the whole suberin biosynthesis pathway. The lipid content analysis confirmed that MdMYB68 regulates the deposition of suberin in cell walls. Furthermore, we also investigated the alteration of the non-lipid cell wall components and showed that MdMYB68 triggers a massive modification of hemicelluloses and pectins. These results were finally supported by the microscopy.DiscussionOnce again, we demonstrated that the heterologous transient expression in N. benthamiana coupled with RNA-seq is a powerful and efficient tool to investigate the function of suberin related transcription factors. Here, we suggest MdMYB68 as a new regulator of the aliphatic and aromatic suberin deposition in apple fruit, and further describe, for the first time, rearrangements occurring in the carbohydrate cell wall matrix, preparing this suberin deposition

Morphohistological study of the different constituents of a banana (Musa 'AAA', cv. 'Grande Naine') embryogenic cell suspension

Five types of cellular aggregates have been characterised in embryogenic cell suspensions of banana (#Musa# 'AAA' 'Grande naine' cv.). Type I corresponded to isolated cells or to small cell aggregates. Type II were composed of embryogenic cells. Type III can be distinguished from type II due to the presence of peripheral proliferation zones with embryonic cells. Type IV were composed of protodermic masses histologically comparable to proembryos. Type V were nodules composed of a central zone of meristematic cells and of an external zone of starchy cells. Each culture flask of a cell line contained a majority of one of the above-mentioned aggregate types. Histological studies of somatic embryo developement on semi-solid regeneration medium showed that there were close similarities between the initial steps of ontogenesis of the embryos and the different cell aggregates in liquid multiplication medium. It appeared that aggregates II-IV of the suspension belong to the same development continuum which reproduces the initial phases of somatic embryo ontogenesis on semi-solid medium. Type V resulted from the development of type IV, for which ontogenesis is hindered by direct contact with 2,4-dichlorophenoxyacetic acid and the shaken liquid multiplication medium. Type I aggregates probably do not belong to the development continuum but rather correspond to the degeneration of the other types of aggregates in the suspension. The presence of intermediate types in the liquid medium reinforces the hypothesis of a relationship between the aggregates. The aggregates tended to develop through time from a majority of type II or III at the beginning of their culture to types IV-V for older suspensions. (Résumé d'auteur

Plant Surface Lipids and Epidermis Development

International audienceThe epidermis has a strategic position at the interface between the plant and the environment. In order to control exchanges with the environment as well as to protect the plant from external threats, the epidermis synthesises and secretes surface lipids to form a continuous, transparent and hydrophobic layer known as the cuticle. Cuticle formation is a strictly epidermal property in plants and all aerial epidermal cells produce some sort of cuticle on their surface. Conversely, all cuticularized plant surfaces are of epidermal origin. This seemingly anodyne observation has surprisingly profound implications in terms of understanding the function of the plant cuticle, since it underlies in part, the difficultly of functionally separating epidermal cell fate specification from cuticle biogenesis

Rapid nanoscale quantitative analysis of plant sphingolipid long-chain bases by GC-MS

International audienceIn eukaryotic organisms, sphingolipids are major structural lipids of biological membranes and perform additional essential functions as signalling molecules. While long-chain bases (LCB), the common precursor to all sphingolipid classes, is represented by only one major molecular species in animals and fungi, up to nine LCB have been found in plants. In the absence of genuine plant sphingolipid references required for proper quantification, we have reinvestigated and optimized a protocol destined to the quantification of total plant LCB that relies on the use of gas chromatography-mass spectrometry (GC-MS). This rapid three-step protocol sequentially involves (1) the release of LCB from biological samples using barium hydroxide solution, (2) their oxidation into aldehydes by metaperiodate, and (3) the subsequent identification/quantification of these aldehydes by GC-MS. It is simple and reliable and enables separation of aldehydes upon their stero-specificity. It further enables the quantification of total LCB from a wide variety of samples including yeast and animal cell culturesIn eukaryotic organisms, sphingolipids are major structural lipids of biological membranes and perform additional essential functions as signalling molecules. While long-chain bases (LCB), the common precursor to all sphingolipid classes, is represented by only one major molecular species in animals and fungi, up to nine LCB have been found in plants. In the absence of genuine plant sphingolipid references required for proper quantification, we have reinvestigated and optimized a protocol destined to the quantification of total plant LCB that relies on the use of gas chromatography-mass spectrometry (GC-MS). This rapid three-step protocol sequentially involves (1) the release of LCB from biological samples using barium hydroxide solution, (2) their oxidation into aldehydes by metaperiodate, and (3) the subsequent identification/quantification of these aldehydes by GC-MS. It is simple and reliable and enables separation of aldehydes upon their stero-specificity. It further enables the quantification of total LCB from a wide variety of samples including yeast and animal cell culture

Overexpression of the epidermis-specific homeodomain-leucine zipper IV transcription factor OUTER CELL LAYER1 in maize identifies target genes involved in lipid metabolism and cuticle biosynthesis

L'article original est publié par The American Society of Plant BiologistsInternational audienceTranscription factors of the homeodomain-leucine zipper IV (HD-ZIP IV) family play crucial roles in epidermis-related processes. To gain further insight into the molecular function of OUTER CELL LAYER1 (OCL1), 14 target genes up- or down-regulated in transgenic maize (Zea mays) plants overexpressing OCL1 were identified. The 14 genes all showed partial coexpression with OCL1 in maize organs, and several of them shared preferential expression in the epidermis with OCL1. They encoded proteins involved in lipid metabolism, defense, envelope-related functions, or cuticle biosynthesis and include ZmWBC11a (for white brown complex 11a), an ortholog of AtWBC11 involved in the transport of wax and cutin molecules. In support of the annotations, OCL1-overexpressing plants showed quantitative and qualitative changes of cuticular wax compounds in comparison with wild-type plants. An increase in C24 to C28 alcohols was correlated with the transcriptional up-regulation of ZmFAR1, coding for a fatty acyl-coenzyme A reductase. Transcriptional activation of ZmWBC11a by OCL1 was likely direct, since transactivation in transiently transformed maize kernels was abolished by a deletion of the activation domain in OCL1 or mutations in the L1 box, a cis-element bound by HD-ZIP IV transcription factors. Our data demonstrate that, in addition to AP2/EREBP and MYB-type transcription factors, members of the HD-ZIP IV family contribute to the transcriptional regulation of genes involved in cuticle biosynthesis

Local energetic regulation of sarcoplasmic and myosin ATPase is differently impaired in rats with heart failure

Local control of ATP/ADP ratio is essential for efficient functioning of cellular ATPases. Since creatine kinase (CK) activity and mitochondrial content are reduced in heart failure (HF), and cardiomyocyte ultrastructure is altered, we hypothesized that these changes may affect the local energetic control of two major cardiac ATPases, the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) and the myosin ATPase. Heart failure was induced by aortic stenosis in rats. Electron microscopy confirmed that failing cardiomyocytes had intracellular disorganization, with fewer contacts between mitochondria and myofibrils. Despite normal SERCA protein content, spontaneous Ca2+ release measurements using Fluo-4 on saponin-permeabilized cardiomyocytes showed a lower SR loading in HF even when endogenous CK and mitochondria were fully activated. Similarly, in permeabilized fibres, SR Ca2+ loading supported by SR-bound CK and mitochondria was significantly reduced in HF (by 49% and 40%, respectively, 43% when both systems were activated, P < 0.05). Alkaline phosphatase treatment had no effect, but glycolytic substrates normalized calcium loading in HF to the sham level. The control by CK and mitochondria of the local ATP/ADP ratio close to the myosin ATPase (estimated by rigor tension) was also significantly impaired in HF fibres (by 32% and 46%, respectively). However, while the contributions of mitochondria and CK to local ATP regeneration were equally depressed in HF for the control of SERCA, mitochondrial contribution was more severely impaired than CK (P < 0.05) with respect to myofilament regulation. These data show that local energetic regulation of essential ATPases is severely impaired in heart failure, and undergoes a complex remodelling as a result of a decreased activity of the ATP-generating systems and cytoarchitecture disorganization