Rôle des acides gras à très longues chaines dans le développement d'arabidopsis thaliana

Chez les plantes, les acides gras à très longues chaînes (AGTLCs) sont les composants des triacyglycerols, des cires épicuticulaires, de la suberine ainsi que des lipides membranaires comme les phospholipides et spingolipides. Leur synthèse s effectue au niveau du Reticulum Endoplasmique (RE) par le complexe élongase. PASTICCIN02 (PAS2) est l homologue de la 3-hydroxy-acyl-CoA-dehydratase Phs1p chez la levure Saccharomyces cerevisae. Nous avons montré que PAS2 est un gène essentiel. A l inverse, l expression du gène Phs1 est capable de complémenter les défauts de développement du mutant pas2-1. De plus, la protéine PAS2 interagit directement au niveau du RE avec la dernière enzyme du complexe, CER10. Nous avons montré qu une altération de l activité de PAS2 entraîne une réduction générale des teneurs en AGTLCs dans toutes les classes lipidiques. La réduction ou l augmentation des teneurs en AGTLLCs obervés respectivement chez un mutant pas2-1 ou chez des plantes surexprimant le gène Phs1, sont associées avec de fortes altérations développementales. En particulier, une mutation pas2-1 entraîne une réduction de la croissance racinaire associée paradoxalement avec une augmentation du nombre de cellules en division. Nos résultats ont montré que cette augmentation est due à des retards et/ou défauts de mise en place de la plaque cellulaire au cours de la cytokinèse. De plus, une mutation pas-2-1 conduit à des altérations de la dynamique membranaire au niveau de la voie sécrétoire et de l endocytose. L ensemble de ces résultats a permis de démontrer que la protéine PAS2 est la 3-acyl-CoA déshydratase du complexe élongase chez Arabidopsis et que les AGTLCs sont des composants essentiels du développement de la plante.In plants, very long chain fatty acids (VLCFAs) are building blocks of triacylglycerols, epicuticular waxes, suberin and membrane lipids such as phospholipids and sphingolipids. They are synthesized by the ER membrane bound elongase complex, which requires four enzymatic steps. PASTICCINO2 (PAS2) is the putative homolog of the yeast 3-hydroxy-acyl-CoA dehydratase (Phs1), the third enzyme of the elongase complex. We showed that Arabidopsis PAS2 is an essential gene and that it was able to complement phs1 lethality. Conversely, the expression of Phs1 was able to complement the developmental defects of the pas2-1 mutant. Moreover, PAS2 protein was found to interact directly in the Endoplasmic Reticulum with CER10, the last enzyme of the elongase complex. We showed that PAS2 impairement led to a strong reduction of VLCFAs in different lipid classes. Reduced or enhanced VLCFAs levels in respectively pas 2-1 mutant Phs1 overexpressing plants were associated with developmental defects. In particular, pas 2-1 mutation led to reduced root growth and paradoxically to a higher incidence of cell divisions. We demonstrated that higher incidence of cell divisions resulted from delayed or defective cell plate formation during cytokinesis. Moreover, our results indicated that VLCFA-dependent membrane dynamics during endocytosis and secretion, was required for the establishment of the cell plate. Collectively our data identified PAS2 as the unique 3-hydroxy-acyl-CoA dehydratase in Arabidopsis and highlighted the essential role of VLCFAs in plant development.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Role of very-long-chain fatty acids in plant development, when chain length does matter

Very long chain fatty acids (VLCFAs) are essential components for eukaryotes. They are elongated by the elongase complex in the endoplasmic reticulum and are incorporated into four major lipid pools (triacylglycerols, waxes, phospholipids, complex sphingolipids). Functional analysis of several components of the elongase complex demonstrated the essential role of VLCFAs in plants, invertebrates and vertebrates. Although VLCFAs changes in the triacylglycerol pool has no consequence for plant development, modifications of the nature and levels of VLCFAs in waxes, phospholipids and complex sphingolipids have, collectively, profound effects on embryo, leaf, root and flower development. VLCFAs levels in epicuticular waxes are critical for the regulation of epidermal fusions during organogenesis. VLCFAs phospholipids and sphingolipids are involved in membrane structure and dynamics regulating cell size but also division and differentiation. This review summarizes the recent findings in plants but also in other organisms, highlighting the importance of very long acyl chain length during development. (C) 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

The complex genetic architecture of shoot growth natural variation in Arabidopsis thaliana

One of the main outcomes of quantitative genetics approaches to natural variation is to reveal the genetic architecture underlying the phenotypic space. Complex genetic architectures are described as including numerous loci (or alleles) with small-effect and/or low-frequency in the populations, interactions with the genetic background, environment or age. Linkage or association mapping strategies will be more or less sensitive to this complexity, so that we still have an unclear picture of its extent. By combining high-throughput phenotyping under two environmental conditions with classical QTL mapping approaches in multiple Arabidopsis thaliana segregating populations as well as advanced near isogenic lines construction and survey, we have attempted to improve our understanding of quantitative phenotypic variation. Integrative traits such as those related to vegetative growth used in this work (highlighting either cumulative growth, growth rate or morphology) all showed complex and dynamic genetic architecture with respect to the segregating population and condition. The more resolutive our mapping approach, the more complexity we uncover, with several instances of QTLs visible in near isogenic lines but not detected with the initial QTL mapping, indicating that our phenotyping accuracy was less limiting than the mapping resolution with respect to the underlying genetic architecture. In an ultimate approach to resolve this complexity, we intensified our phenotyping effort to target specifically a 3Mb-region known to segregate for a major quantitative trait gene, using a series of selected lines recombined every 100kb. We discovered that at least 3 other independent QTLs had remained hidden in this region, some with trait- or condition-specific effects, or opposite allelic effects. If we were to extrapolate the figures obtained on this specific region in this particular cross to the genome- and species-scale, we would predict hundreds of causative loci of detectable phenotypic effect controlling these growth-related phenotypes. Author summary The question of the complexity of the genetic variants underlying diversity in plant size and shape is central in evolutionary biology to better understand the impacts of selection and adaptation. In this work, we have combined the high resolution of a robotized platform designed to grow Arabidopsis plants under strictly-controlled conditions and the power of quantitative genetics approaches to map the individual genetic components (the 'QTLs') controlling diverse phenotypes, and hence reveal the so-called 'genetic architecture' of these traits. We show that the more we increase our resolution to map QTLs, the more complex of a genetic architecture we reveal. For instance, by focusing all of our mapping power on a small region representing 2.5% of the genome in an unprecedented phenotyping effort, we reveal that several independent QTLs had remained hidden in this region beyond a major-effect QTL that is always clearly visible. If this region is representative of the genome, this means that our current understanding misses potentially hundreds of variants finely controlling traits of evolutionary or agronomical interest

Mild drought in the vegetative stage induces phenotypic, gene expression and DNA methylation plasticity in Arabidopsis but no transgenerational effects

International audienceWhether environmentally-induced changes in phenotypes can be heritable is a topic with revived interest. In plants, heritable trait variation can occur without DNA sequence mutations through epigenetic mechanisms involving DNA methylation. However, it remains unknown if this other system of inheritance responds to environmental changes and if it can provide a rapid way for plants to generate adaptive heritable phenotypic variation. To obtain a comprehensive assessment of potential transgenerational effects induced by the environment, we subjected four natural accessions as well as the reference accession Col-0 of A. thaliana to mild drought in a multigenerational design. As expected, plastic responses to drought were observed in each accession, as well as a number of intergenerational effects of parental environments. However, after an intervening generation without stress, descendants of stressed and non-stressed plants were phenotypically indistinguishable, except for very few trait-based parental effects and irrespective of whether they were grown in control conditions or under water deficit. In addition, genome-wide analysis of DNA methylation and gene expression in the reference accession Col-0 demonstrated that, while mild drought induced changes in the DNA methylome of exposed plants, variants were not inherited. We conclude that mild drought stress does not induce transgenerational epigenetic effects

Arabidopsis PASTICCINO2 Is an Antiphosphatase Involved in Regulation of Cyclin-Dependent Kinase A

PASTICCINO2 (PAS2), a member of the protein Tyr phosphatase-like family, is conserved among all eukaryotes and is characterized by a mutated catalytic site. The cellular functions of the Tyr phosphatase-like proteins are still unknown, even if they are essential in yeast and mammals. Here, we demonstrate that PAS2 interacts with a cyclin-dependent kinase (CDK) that is phosphorylated on Tyr and not with its unphosphorylated isoform. Phosphorylation of the conserved regulatory Tyr-15 is involved in the binding of CDK to PAS2. Loss of the PAS2 function dephosphorylated Arabidopsis thaliana CDKA;1 and upregulated its kinase activity. In accordance with its role as a negative regulator of the cell cycle, overexpression of PAS2 slowed down cell division in suspension cell cultures at the G2-to-M transition and early mitosis and inhibited Arabidopsis seedling growth. The latter was accompanied by altered leaf development and accelerated cotyledon senescence. PAS2 was localized in the cytoplasm of dividing cells but moved into the nucleus upon cell differentiation, suggesting that the balance between cell division and differentiation is regulated through the interaction between CDKA;1 and the antiphosphatase PAS2

Very-Long-Chain Fatty Acids Are Involved in Polar Auxin Transport and Developmental Patterning in \u3ci\u3eArabidopsis\u3c/i\u3e

Very-long-chain fatty acids (VLCFAs) are essential for many aspects of plant development and necessary for the synthesis of seed storage triacylglycerols, epicuticular waxes, and sphingolipids. Identification of the acetyl-CoA carboxylase PASTICCINO3 and the 3-hydroxy acyl-CoA dehydratase PASTICCINO2 revealed that VLCFAs are important for cell proliferation and tissue patterning. Here, we show that the immunophilin PASTICCINO1 (PAS1) is also required for VLCFA synthesis. Impairment of PAS1 function results in reduction of VLCFA levels that particularly affects the composition of sphingolipids, known to be important for cell polarity in animals. Moreover, PAS1 associates with several enzymes of the VLCFA elongase complex in the endoplasmic reticulum. The pas1 mutants are deficient in lateral root formation and are characterized by an abnormal patterning of the embryo apex, which leads to defective cotyledon organogenesis. Our data indicate that in both tissues, defective organogenesis is associated with the mistargeting of the auxin efflux carrier PIN FORMED1 in specific cells, resulting in local alteration of polar auxin distribution. Furthermore, we show that exogenous VLCFAs rescue lateral root organogenesis and polar auxin distribution, indicating their direct involvement in these processes. Based on these data, we propose that PAS1 acts as a molecular scaffold for the fatty acid elongase complex in the endoplasmic reticulum and that the resulting VLCFAs are required for polar auxin transport and tissue patterning during plant development

Very-Long-Chain Fatty Acids Are Involved in Polar Auxin Transport and Developmental Patterning in Arabidopsis[W]

This work identifies the immunophilin PASTICCINO1 as a member of the complex necessary for very-long-chain fatty acid synthesis and demonstrates that fatty acids are directly involved in auxin carrier distribution during organogenesis