RESUMO
In angiosperms, double fertilization of the embryo sac initiates the development of the embryo and the endosperm. In Arabidopsis thaliana, an exalbuminous species, the endosperm is reduced to one cell layer during seed maturation and reserves such as oil are massively deposited in the enlarging embryo. Here, we consider the strikingly different fatty acid (FA) compositions of the oils stored in the two zygotic tissues. Endosperm oil is enriched in ω-7 monounsaturated FAs, that represent more than 20 mol% of total FAs, whereas these molecular species are 10-fold less abundant in the embryo. Two closely related transcription factors, MYB118 and MYB115, are transcriptionally induced at the onset of the maturation phase in the endosperm and share a set of transcriptional targets. Interestingly, the endosperm oil of myb115 myb118 double mutants lacks ω-7 FAs. The identification of two Δ9 palmitoyl-ACP desaturases responsible for ω-7 FA biosynthesis, which are activated by MYB115 and MYB118 in the endosperm, allows us to propose a model for the transcriptional control of oil FA composition in this tissue. In addition, an initial characterization of the structure-function relationship for these desaturases reveals that their particular substrate specificity is conferred by amino acid residues lining their substrate pocket that distinguish them from the archetype Δ9 stearoyl-ACP desaturase.
Assuntos
Arabidopsis/metabolismo , Endosperma/metabolismo , Oxigenases de Função Mista/metabolismo , Sementes/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Endosperma/genética , Ácidos Graxos Monoinsaturados/metabolismo , Oxigenases de Função Mista/genética , Sementes/genética , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Lipid droplets/oil bodies (OBs) are lipid-storage organelles that play a crucial role as an energy resource in a variety of eukaryotic cells. Lipid stores are mobilized in the case of food deprivation or high energy demands--for example, during certain developmental processes in animals and plants. OB degradation is achieved by lipases that hydrolyze triacylglycerols (TAGs) into free fatty acids and glycerol. In the model plant Arabidopsis thaliana, Sugar-Dependent 1 (SDP1) was identified as the major TAG lipase involved in lipid reserve mobilization during seedling establishment. Although the enzymatic activity of SDP1 is associated with the membrane of OBs, its targeting to the OB surface remains uncharacterized. Here we demonstrate that the core retromer, a complex involved in protein trafficking, participates in OB biogenesis, lipid store degradation, and SDP1 localization to OBs. We also report an as-yet-undescribed mechanism for lipase transport in eukaryotic cells, with SDP1 being first localized to the peroxisome membrane at early stages of seedling growth and then possibly moving to the OB surface through peroxisome tubulations. Finally, we show that the timely transfer of SDP1 to the OB membrane requires a functional core retromer. In addition to revealing previously unidentified functions of the retromer complex in plant cells, our work provides unanticipated evidence for the role of peroxisome dynamics in interorganelle communication and protein transport.
Assuntos
Arabidopsis/genética , Hidrolases de Éster Carboxílico/metabolismo , Gotículas Lipídicas/química , Peroxissomos/química , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Genes de Plantas , Germinação , Lipase/metabolismo , Lipídeos/química , Microscopia Confocal , Mutação , Oxigênio/química , Peroxissomos/metabolismo , Fenótipo , Raízes de Plantas/metabolismo , Transporte Proteico , Plântula/crescimento & desenvolvimento , Sementes/metabolismoRESUMO
Small proteins have long been overlooked due to their poor annotation and the experimental challenges they pose. However, in recent years, their role in various processes has started to emerge, opening new research avenues. Here, we present the isolation and characterization of two allelic mutants, twisted seed1-1 (tws1-1) and tws1-2, which exhibit an array of developmental and biochemical phenotypes in Arabidopsis (Arabidopsis thaliana) seeds. We have identified AT5G01075 as the subtending gene encoding a small protein of 81 amino acids localized in the endoplasmic reticulum. TWS1 is strongly expressed in seeds, where it regulates both embryo development and accumulation of storage compounds. TWS1 loss-of-function seeds exhibit increased starch, sucrose, and protein accumulation at the detriment of fatty acids. TWS1 is also expressed in vegetative and reproductive tissues, where it is responsible for proper epidermal cell morphology and overall plant growth. At the cellular level, TWS1 is responsible for cuticle deposition on epidermal cells and organization of the endomembrane system. Finally, we show that TWS1 is a single-copy gene in Arabidopsis, and it is specifically conserved among angiosperms.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/embriologia , Desenvolvimento Vegetal , Sementes/embriologia , Alelos , Sequência de Aminoácidos , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Carbono/farmacologia , Retículo Endoplasmático/efeitos dos fármacos , Retículo Endoplasmático/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Mutação/genética , Fenótipo , Desenvolvimento Vegetal/efeitos dos fármacos , Desenvolvimento Vegetal/genética , Epiderme Vegetal/efeitos dos fármacos , Epiderme Vegetal/metabolismo , Plantas Geneticamente Modificadas , Sementes/efeitos dos fármacos , Sementes/ultraestrutura , Vacúolos/efeitos dos fármacos , Vacúolos/metabolismoRESUMO
In oleaginous seeds, lipids--stored in organelles called oil bodies (OBs)--are degraded post-germinatively to provide carbon and energy for seedling growth. To date, little is known about how OB coat proteins, known as oleosins, control OB dynamics during seed germination. Here, we demonstrated that the sequential proteolysis of the five Arabidopsis thaliana oleosins OLE1-OLE5 begins just prior to lipid degradation. Several post-translational modifications (e.g. phosphorylation and ubiquination) of oleosins were concomitant with oleosin degradation. Phosphorylation occurred only on the minor OLE5 and on an 8 kDa proteolytic fragment of OLE2. A combination of immunochemical and proteomic approaches revealed ubiquitination of the four oleosins OLE1-OLE4 at the onset of OB mobilization. Ubiquitination topology was surprisingly complex. OLE1 and OLE2 were modified by three distinct and predominantly exclusive motifs: monoubiquitin, K48-linked diubiquitin (K48Ub(2)) and K63-linked diubiquitin. Ubiquitinated oleosins may be channeled towards specific degradation pathways according to ubiquitination type. One of these pathways was identified as the ubiquitin-proteasome pathway. A proteasome inhibitor (MG132) reduced oleosin degradation and induced cytosolic accumulation of K48Ub(2)-oleosin aggregates. These results indicate that K48Ub(2)-modified oleosins are selectively extracted from OB coat and degraded by the proteasome. Proteasome inhibition also reduced lipid hydrolysis, providing in vivo evidence that oleosin degradation is required for lipid mobilization.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Gotículas Lipídicas/metabolismo , Plântula/metabolismo , Ubiquitina/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Inibidores de Cisteína Proteinase/farmacologia , Germinação , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Immunoblotting , Leupeptinas/farmacologia , Microscopia Confocal , Fosforilação , Plantas Geneticamente Modificadas , Complexo de Endopeptidases do Proteassoma/metabolismo , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Proteólise/efeitos dos fármacos , Proteômica/métodos , Plântula/genética , Plântula/crescimento & desenvolvimento , Sementes/genética , Sementes/crescimento & desenvolvimento , Sementes/metabolismo , Fatores de Tempo , UbiquitinaçãoRESUMO
MAIN CONCLUSION: The protein, phospholipid and sterol composition of the oil body surface from the seeds of two rapeseed genotypes was compared in order to explain their contrasted oil extractability. In the mature seeds of oleaginous plants, storage lipids accumulate in specialized structures called oil bodies (OBs). These organelles consist of a core of neutral lipids surrounded by a phospholipid monolayer in which structural proteins are embedded. The physical stability of OBs is a consequence of the interactions between proteins and phospholipids. A detailed study of OB characteristics in mature seeds as well as throughout seed development was carried out on two contrasting rapeseed genotypes Amber and Warzanwski. These two accessions were chosen because they differ dramatically in (1) crushing ability, (2) oil extraction yield and, (3) the stability of purified OBs. Warzanwski has higher crushing ability, better oil extraction yield and less stable purified OBs than Amber. OB morphology was investigated in situ using fluorescence microscopy, transmission electron microscopy and pulsed field gradient NMR. During seed development, OB diameter first increased and then decreased 30 days after pollination in both Amber and Warzanwski embryos. In mature seeds, Amber OBs were significantly smaller. The protein, phospholipid and sterol composition of the hemi-membrane was compared between the two accessions. Amber OBs were enriched with H-oleosins and steroleosins, suggesting increased coverage of the OB surface consistent with their higher stability. The nature and composition of phospholipids and sterols in Amber OBs suggest that the hemi-membrane would have a more rigid structure than that of Warzanwski OBs.
Assuntos
Brassica rapa/embriologia , Brassica rapa/genética , Gotículas Lipídicas/metabolismo , Óleos de Plantas/isolamento & purificação , Sementes/anatomia & histologia , Sementes/metabolismo , Brassica rapa/anatomia & histologia , Eletroforese em Gel Bidimensional , Genótipo , Espectroscopia de Ressonância Magnética , Fosfolipídeos/metabolismo , Fitosteróis/metabolismo , Proteínas de Plantas/metabolismo , Sementes/genética , Sementes/ultraestrutura , Tocoferóis/metabolismoRESUMO
Maize (Zea mays) is an important C4 plant due to its widespread use as a cereal and energy crop. A second-generation genome-scale metabolic model for the maize leaf was created to capture C4 carbon fixation and investigate nitrogen (N) assimilation by modeling the interactions between the bundle sheath and mesophyll cells. The model contains gene-protein-reaction relationships, elemental and charge-balanced reactions, and incorporates experimental evidence pertaining to the biomass composition, compartmentalization, and flux constraints. Condition-specific biomass descriptions were introduced that account for amino acids, fatty acids, soluble sugars, proteins, chlorophyll, lignocellulose, and nucleic acids as experimentally measured biomass constituents. Compartmentalization of the model is based on proteomic/transcriptomic data and literature evidence. With the incorporation of information from the MetaCrop and MaizeCyc databases, this updated model spans 5,824 genes, 8,525 reactions, and 9,153 metabolites, an increase of approximately 4 times the size of the earlier iRS1563 model. Transcriptomic and proteomic data have also been used to introduce regulatory constraints in the model to simulate an N-limited condition and mutants deficient in glutamine synthetase, gln1-3 and gln1-4. Model-predicted results achieved 90% accuracy when comparing the wild type grown under an N-complete condition with the wild type grown under an N-deficient condition.
Assuntos
Modelos Biológicos , Nitrogênio/metabolismo , Folhas de Planta/metabolismo , Zea mays/genética , Zea mays/metabolismo , Disponibilidade Biológica , Biomassa , Perfilação da Expressão Gênica , Genoma de Planta , Metaboloma , Mutação , Nitrogênio/farmacocinética , Proteoma/metabolismoRESUMO
Oil bodies (OBs) are seed-specific lipid storage organelles that allow the accumulation of neutral lipids that sustain plantlet development after the onset of germination. OBs are covered with specific proteins embedded in a single layer of phospholipids. Using fluorescent dyes and confocal microscopy, we monitored the dynamics of OBs in living Arabidopsis (Arabidopsis thaliana) embryos at different stages of development. Analyses were carried out with different genotypes: the wild type and three mutants affected in the accumulation of various oleosins (OLE1, OLE2, and OLE4), three major OB proteins. Image acquisition was followed by a detailed statistical analysis of OB size and distribution during seed development in the four dimensions (x, y, z, and t). Our results indicate that OB size increases sharply during seed maturation, in part by OB fusion, and then decreases until the end of the maturation process. In single, double, and triple mutant backgrounds, the size and spatial distribution of OBs are modified, affecting in turn the total lipid content, which suggests that the oleosins studied have specific functions in the dynamics of lipid accumulation.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/embriologia , Arabidopsis/metabolismo , Corpos de Inclusão/metabolismo , Óleos de Plantas/metabolismo , Sementes/crescimento & desenvolvimento , Sementes/metabolismo , Germinação , Imageamento Tridimensional , Fenótipo , Análise de Regressão , Coloração e RotulagemRESUMO
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.
Assuntos
Arabidopsis/metabolismo , Ácidos Graxos/metabolismo , Ácidos Indolacéticos/metabolismo , Arabidopsis/embriologia , Arabidopsis/crescimento & desenvolvimentoRESUMO
Elucidating the mechanisms that control seed development, metabolism, and physiology is a fundamental issue in biology. Michel Caboche had long been a catalyst for seed biology research in France up until his untimely passing away last year. To honour his memory, we have updated a review written under his coordination in 2010 entitled "Arabidopsis seed secrets unravelled after a decade of genetic and omics-driven research". This review encompassed different molecular aspects of seed development, reserve accumulation, dormancy and germination, that are studied in the lab created by M. Caboche. We have extended the scope of this review to highlight original experimental approaches implemented in the field over the past decade such as omics approaches aimed at investigating the control of gene expression, protein modifications, primary and specialized metabolites at the tissue or even cellular level, as well as seed biodiversity and the impact of the environment on seed quality.
L'élucidation des mécanismes qui contrôlent le développement, le métabolisme et la physiologie des graines est une question fondamentale en biologie. Michel Caboche a longtemps été un catalyseur de la recherche en biologie des graines en France jusqu'à son décès prématuré l'année dernière. Pour honorer sa mémoire, nous avons mis à jour une revue écrite sous sa coordination en 2010 intitulée « Arabidopsis seed secrets unravelled after a decade of genetic and omics-driven research ¼. Cette revue englobait différents aspects moléculaires du développement des graines, de l'accumulation des réserves, de la dormance et de la germination, qui sont étudiés dans le laboratoire créé par M. Caboche. Nous avons étendu la portée de cette revue pour mettre en évidence des approches expérimentales originales mises en Åuvre dans le domaine au cours de la dernière décennie, telles que les approches omiques visant à étudier le contrôle de l'expression des gènes, les modifications des protéines, les métabolites primaires et spécialisés au niveau des tissus ou même des cellules, tout en tenant compte de la biodiversité des graines et de l'impact de l'environnement sur leur qualité.
Assuntos
Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Sementes/genética , Biologia Molecular , Biologia , França , Germinação/genética , Dormência de Plantas/genética , Regulação da Expressão Gênica de PlantasRESUMO
The polyunsaturated fatty acids (PUFAs) linoleic acid (18:2) and alpha-linolenic acid (18:3) in triacylglycerols (TAG) are major factors affecting the quality of plant oils for human health, as well as for biofuels and other renewable applications. These PUFAs are essential fatty acids for animals and plants, but also are the source of unhealthy trans fats during the processing of many foodstuffs. PUFAs 18:2 and 18:3 are synthesized in developing seeds by the desaturation of oleic acid (18:1) esterified on the membrane lipid phosphatidylcholine (PC) on the endoplasmic reticulum. The reactions and fluxes involved in this metabolism are incompletely understood, however. Here we show that a previously unrecognized enzyme, phosphatidylcholine:diacylglycerol cholinephosphotransferase (PDCT), encoded by the Arabidopsis ROD1 gene, is a major reaction for the transfer of 18:1 into PC for desaturation and also for the reverse transfer of 18:2 and 18:3 into the TAG synthesis pathway. The PDCT enzyme catalyzes transfer of the phosphocholine headgroup from PC to diacylglycerol, and mutation of rod1 reduces 18:2 and 18:3 accumulation in seed TAG by 40%. Our discovery of PDCT is important for understanding glycerolipid metabolism in plants and other organisms, and provides tools to modify the fatty acid compositions of plant oils for improved nutrition, biofuel, and other purposes.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/enzimologia , Arabidopsis/genética , Genes de Plantas , Fosfotransferases/genética , Transferases (Outros Grupos de Fosfato Substituídos)/genética , Triglicerídeos/metabolismo , Sequência de Aminoácidos , Proteínas de Arabidopsis/química , Cruzamentos Genéticos , Ácidos Graxos/análise , Marcação por Isótopo , Dados de Sequência Molecular , Mutação/genética , Fosfatidilcolinas/metabolismo , Fosfotransferases/metabolismo , Filogenia , Sementes/química , Análise de Sequência de Proteína , Transferases (Outros Grupos de Fosfato Substituídos)/química , Triglicerídeos/biossínteseRESUMO
The PII protein is an integrator of central metabolism and energy levels. In Arabidopsis, allosteric sensing of cellular energy and carbon levels alters the ability of PII to interact with target enzymes such as N-acetyl-l-glutamate kinase and heteromeric acetyl-coenzyme A carboxylase, thereby modulating the biological activity of these plastidial ATP- and carbon-consuming enzymes. A quantitative reverse transcriptase-polymerase chain reaction approach revealed a threefold induction of the AtGLB1 gene (At4g01900) encoding PII during early seed maturation. The activity of the AtGLB1 promoter was consistent with this pattern. A complementary set of molecular and genetic analyses showed that WRINKLED1, a transcription factor known to induce glycolytic and fatty acid biosynthetic genes at the onset of seed maturation, directly controls AtGLB1 expression. Immunoblot analyses and immunolocalization experiments using anti-PII antibodies established that PII protein levels faithfully reflected AtGLB1 mRNA accumulation. At the subcellular level, PII was observed in plastids of maturing embryos. To further investigate the function of PII in seeds, comprehensive functional analyses of two pII mutant alleles were carried out. A transient increase in fatty acid production was observed in mutant seeds at a time when PII protein content was found to be maximal in wild-type seeds. Moreover, minor though statistically significant modifications of the fatty acid composition were measured in pII seeds, which exhibited decreased amounts of modified (elongated, desaturated) fatty acid species. The results obtained outline a role for PII in the fine tuning of fatty acid biosynthesis and partitioning in seeds.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Ácidos Graxos/biossíntese , Proteínas PII Reguladoras de Nitrogênio/metabolismo , Sementes/metabolismo , Fatores de Transcrição/metabolismo , Arabidopsis/crescimento & desenvolvimento , Perfilação da Expressão Gênica , Modelos Biológicos , Mutação , Plastídeos/metabolismo , Regiões Promotoras Genéticas , Sementes/crescimento & desenvolvimentoRESUMO
Seeds play a fundamental role in colonization of the environment by spermatophytes, and seeds harvested from crops are the main food source for human beings. Knowledge of seed biology is therefore important for both fundamental and applied issues. This review on seed biology illustrates the important progress made in the field of Arabidopsis seed research over the last decade. Access to 'omics' tools, including the inventory of genes deduced from sequencing of the Arabidopsis genome, has speeded up the analysis of biological functions operating in seeds. This review covers the following processes: seed and seed coat development, seed reserve accumulation, seed dormancy and seed germination. We present new insights in these various fields and describe ongoing biotechnology approaches to improve seed characteristics in crops.
Assuntos
Arabidopsis/genética , Genômica , Sementes/crescimento & desenvolvimento , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Biotecnologia/tendências , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Genoma de Planta , Germinação , Reguladores de Crescimento de Plantas/metabolismo , Proteínas de Armazenamento de Sementes/metabolismo , Sementes/genética , Sementes/metabolismoRESUMO
Very-long-chain fatty acids (VLCFAs) are synthesized as acyl-CoAs by the endoplasmic reticulum-localized elongase multiprotein complex. Two Arabidopsis genes are putative homologues of the recently identified yeast 3-hydroxy-acyl-CoA dehydratase (PHS1), the third enzyme of the elongase complex. We showed that Arabidopsis PASTICCINO2 (PAS2) was able to restore phs1 cytokinesis defects and sphingolipid long chain base overaccumulation. Conversely, the expression of PHS1 was able to complement the developmental defects and the accumulation of long chain bases of the pas2-1 mutant. The pas2-1 mutant was characterized by a general reduction of VLCFA pools in seed storage triacylglycerols, cuticular waxes, and complex sphingolipids. Most strikingly, the defective elongation cycle resulted in the accumulation of 3-hydroxy-acyl-CoA intermediates, indicating premature termination of fatty acid elongation and confirming the role of PAS2 in this process. We demonstrated by in vivo bimolecular fluorescence complementation that PAS2 was specifically associated in the endoplasmic reticulum with the enoyl-CoA reductase CER10, the fourth enzyme of the elongase complex. Finally, complete loss of PAS2 function is embryo lethal, and the ectopic expression of PHS1 led to enhanced levels of VLCFAs associated with severe developmental defects. Altogether these results demonstrate that the plant 3-hydroxy-acyl-CoA dehydratase PASTICCINO2 is an essential and limiting enzyme in VLCFA synthesis but also that PAS2-derived VLCFA homeostasis is required for specific developmental processes.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Arabidopsis/crescimento & desenvolvimento , Regulação da Expressão Gênica de Plantas , Acil Coenzima A/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Ácidos Graxos/metabolismo , Teste de Complementação Genética , Hidroliases/genética , Mutação , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genética , Sementes/metabolismoRESUMO
The hydroxysteroid dehydrogenase HSD1, identified in the proteome of oil bodies from mature Arabidopsis seeds, is encoded by At5g50600 and At5g50700, two gene copies anchored on a duplicated region of chromosome 5. Using a real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) approach, the accumulation of HSD1 mRNA was shown to be specifically and highly induced in oil-accumulating tissues of maturing seeds. HSD1 mRNA disappeared during germination. The activity of HSD1 promoter and the localization of HSD1 transcripts by in situ hybridization were consistent with this pattern. A complementary set of molecular and genetic analyses showed that HSD1 is a target of LEAFY COTYLEDON2, a transcriptional regulator able to bind the promoter of HSD1. Immunoblot analyses and immunolocalization experiments using anti-AtHSD1 antibodies established that the pattern of HSD1 deposition faithfully reflected mRNA accumulation. At the subcellular level, the study of HSD1:GFP fusion proteins showed the targeting of HSD1 to the surface of oil bodies. Transgenic lines overexpressing HSD1 were then obtained to test the importance of proper transcriptional regulation of HSD1 in seeds. Whereas no impact on oil accumulation could be detected, transgenic seeds exhibited lower cold and light requirements to break dormancy, germinate and mobilize storage lipids. Interestingly, overexpressors of HSD1 over-accumulated HSD1 protein in seeds but not in vegetative organs, suggesting that post-transcriptional regulations exist that prevent HSD1 accumulation in tissues deprived of oil bodies.
Assuntos
11-beta-Hidroxiesteroide Desidrogenases/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Sementes/metabolismo , Triglicerídeos/biossíntese , 11-beta-Hidroxiesteroide Desidrogenases/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , DNA Complementar/genética , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Germinação/genética , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/metabolismo , Regiões Promotoras Genéticas , RNA Mensageiro/metabolismo , RNA de Plantas/metabolismo , Sementes/genética , Sementes/fisiologia , Fatores de Transcrição/metabolismoRESUMO
Many organisms among the different kingdoms store reserve lipids in discrete subcellular organelles called lipid bodies. In plants, lipid bodies can be found in seeds but also in fruits (olives, ...), and in leaves (plastoglobules). These organelles protect plant lipid reserves against oxidation and hydrolysis until seed germination and seedling establishment. They can be stabilized by specific structural proteins, namely the oleosins and caleosins, which act as natural emulsifiers. Considering the putative role of some of them in controlling the size of lipid bodies, these proteins may constitute important targets for seed improvement both in term of oil seed yield and optimization of technological processes for extraction of oil and storage proteins. We present here an overview of the data on the structure of these proteins, which are scarce, and sometimes contradictory and on their functional roles.
Assuntos
Metabolismo dos Lipídeos , Organelas/metabolismo , Proteínas de Plantas/fisiologia , Sementes/metabolismo , Proteínas de Ligação ao Cálcio/fisiologia , Germinação/fisiologia , Interações Hidrofóbicas e Hidrofílicas , Óleos de Plantas/metabolismo , Proteínas de Plantas/química , Conformação Proteica , Estrutura Terciária de Proteína , Sementes/crescimento & desenvolvimento , Relação Estrutura-Atividade , Triglicerídeos/metabolismoRESUMO
LEAFY COTYLEDON 2 (LEC2) is a key regulator of seed maturation in Arabidopsis. To unravel some of its complex pleiotropic functions, analyses were performed with transgenic plants expressing an inducible LEC2:GR protein. The chimeric protein is functional and can complement lec2 mutation. Interestingly, the induction of LEC2 leads to the accumulation of storage oil in leaves. In addition, short-term induction and use of translation inhibitors allowed to demonstrate that LEC2 can directly trigger the accumulation of seed specific mRNAs. Consistent with these results, the expression of three other major seed regulators namely, LEC1, FUS3, and ABI3 were also induced by LEC2 activation.
Assuntos
Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas , Folhas de Planta/genética , Óleos de Plantas , RNA Mensageiro/metabolismo , Sementes/genética , Fatores de Transcrição/metabolismo , Arabidopsis/química , Arabidopsis/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Proteínas Estimuladoras de Ligação a CCAAT/genética , Proteínas Estimuladoras de Ligação a CCAAT/metabolismo , Genótipo , Metabolismo dos Lipídeos , Fenótipo , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Sementes/fisiologia , Fatores de Transcrição/genéticaRESUMO
The seed development and composition of Medicago truncatula Gaertn., the new model plant for grain legumes, was studied using nine genotypes of the species complex: M. truncatula-Medicago littoralis (M. truncatula). The seed development of M. truncatula was very similar to that of other legumes, the only notable exception being the presence, in the mature seed, of an endosperm layer that is absent in grain legumes. During early embryogenesis and until mid-maturation, transient storage of starch occurred in the seed coat and embryo. This temporary storage probably contributed to the early development of the embryo and reserve synthesis. During maturation the synthesis and accumulation of proteins and oil took place at quasi-constant rates. Conversely oligosaccharides, mainly stachyose, were synthesised only during late maturation and at the beginning of desiccation. Proteins represented the major class of storage compounds and their average amino acid composition was found to be very close to that of pea and robust in various environmental conditions. Similar compositions between the two species and other grain legumes were also found for the fatty acids and the soluble sugars; most of these characters varied depending on the various environmental conditions used for seed production. All these similarities fully justify the use of M. truncatula as a model plant for genomic approaches to grain legume improvement. The major difference between M. truncatula seeds and European grain legume seeds resides in the nature of their carbon storage namely triacylglycerides for M. truncatula and starch for pea and faba bean.
Assuntos
Medicago truncatula/crescimento & desenvolvimento , Sementes/crescimento & desenvolvimento , Aminoácidos/biossíntese , Ácidos Graxos/biossíntese , Regulação da Expressão Gênica de Plantas , Genótipo , Medicago truncatula/metabolismo , Nitrogênio/análise , Oligossacarídeos/biossíntese , Proteínas de Plantas/metabolismo , Sementes/metabolismo , Amido/biossínteseRESUMO
Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables.
RESUMO
Oil from oleaginous seeds is mainly composed of triacylglycerols. Very long chain fatty acids (VLCFAs) are major constituents of triacylglycerols in many seed oils and represent valuable feedstock for industrial purposes. To identify genetic factors governing natural variability in VLCFA biosynthesis, a quantitative trait loci (QTL) analysis using a recombinant inbred line population derived from a cross between accessions Bay-0 and Shahdara was performed in Arabidopsis thaliana. Two fatty acid chain length ratio (CLR) QTL were identified, with one major locus, CLR.2, accounting for 77% of the observed phenotypic variation. A fine mapping and candidate gene approach showed that a key enzyme of the fatty acid elongation pathway, the ß-ketoacyl-CoA synthase 18 (KCS18), was responsible for the CLR.2 QTL detected between Bay-0 and Shahdara. Association genetics and heterologous expression in yeast cells identified a single point mutation associated with an alteration of KCS18 activity, uncovering the molecular bases for the modulation of VLCFA content in these two natural populations of Arabidopsis. Identification of this kcs18 mutant with altered activity opens new perspectives for the modulation of oil composition in crop plants.
Assuntos
3-Oxoacil-(Proteína de Transporte de Acila) Sintase/fisiologia , Proteínas de Arabidopsis/fisiologia , Arabidopsis/metabolismo , Ácidos Graxos/metabolismo , Sementes/metabolismo , 3-Oxoacil-(Proteína de Transporte de Acila) Sintase/genética , 3-Oxoacil-(Proteína de Transporte de Acila) Sintase/metabolismo , Substituição de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Mapeamento Cromossômico , Cromossomos de Plantas , Cruzamentos Genéticos , Ácidos Graxos/química , Estudos de Associação Genética , Fenótipo , Mutação Puntual , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Isoformas de Proteínas/fisiologia , Estrutura Terciária de Proteína , Locos de Características Quantitativas , Sementes/genéticaRESUMO
Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables.