Synthesis of the major oil-body membrane protein in developing rapeseed (Brassica napus) embryos. Integration with storage-lipid and storage-protein synthesis and implications for the mechanism of oil-body formation

Breeding Canola (Brassica napus L.) for Protein in Feed and Food

Interest in canola (Brassica napus L.). In response to this interest, scientists have been tasked with altering and optimizing the protein production chain to ensure canola proteins are safe for consumption and economical to produce. Specifically, the role of plant breeders in developing suitable varieties with the necessary protein profiles is crucial to this interdisciplinary endeavour. In this article, we aim to provide an overarching review of the canola protein chain from the perspective of a plant breeder, spanning from the genetic regulation of seed storage proteins in the crop to advancements of novel breeding technologies and their application in improving protein quality in canola. A review on the current uses of canola meal in animal husbandry is presented to underscore potential limitations for the consumption of canola meal in mammals. General discussions on the allergenic potential of canola proteins and the regulation of novel food products are provided to highlight some of the challenges that will be encountered on the road to commercialization and general acceptance of canola protein as a dietary protein source.

Prediction and analysis of antimicrobial peptides from rapeseed protein using in silico approach

The purpose of this study was to evaluate the potential of rapeseed proteins including Napin, Cruciferin, and Oleosin as precursors of antimicrobial peptides (AMPs), and to investigate physicochemical properties, secondary structures, toxicity, and allergenicity of AMPs using several bioinformatics tools such as BIOPEP, CAMP, APD, SOPMA, ToxinPred, and AllergenFP. A total of 26 novel AMPs were obtained by in silico hydrolysis using nine proteases, and six peptides were tested positive by all the four algorithms including Random Forest (RF), Support Vector Machines (SVM), Artificial Neural Network (ANN), and Discriminant Analysis (DA). More AMPs were generated from Cruciferin than from Napin and Oleosin. Trypsin was the most effective enzyme for AMPs production compared with other used proteases. About two-third of peptides were cationic. Interestingly, most peptides were extended AMPs. All AMPs were predicted to be non-toxic, and 14 peptides were non-allergenic. These results indicate that rapeseed protein is a good potential source of AMPs as demonstrated by in silico analyses and the theoretical knowledge obtained provides a basis for further development and production of rapeseed AMPs. PRACTICAL APPLICATIONS: Rapeseed protein is a high-quality plant protein resource. However, it is usually used as animal feed or fertilizer. Effective enzymatic hydrolysis of rapeseed protein can release bioactive peptides and improve the utilization value. This study indicates that rapeseed protein is a good potential source of AMPs as demonstrated by in silico analyses. The theoretical knowledge obtained provides a basis for further development and production of rapeseed AMPs.

Unravelling the Complex Interplay of Transcription Factors Orchestrating Seed Oil Content in Brassica napus L

Transcription factors (TFs) and their complex interplay are essential for directing specific genetic programs, such as responses to environmental stresses, tissue development, or cell differentiation by regulating gene expression. Knowledge regarding TF-TF cooperations could be promising in gaining insight into the developmental switches between the cultivars of Brassica napus L., namely Zhongshuang11 (ZS11), a double-low accession with high-oil- content, and Zhongyou821 (ZY821), a double-high accession with low-oil-content. In this regard, we analysed a time series RNA-seq data set of seed tissue from both of the cultivars by mainly focusing on the monotonically expressed genes (MEGs). The consideration of the MEGs enables the capturing of multi-stage progression processes that are orchestrated by the cooperative TFs and, thus, facilitates the understanding of the molecular mechanisms determining seed oil content. Our findings show that TF families, such as NAC, MYB, DOF, GATA, and HD-ZIP are highly involved in the seed developmental process. Particularly, their preferential partner choices as well as changes in their gene expression profiles seem to be strongly associated with the differentiation of the oil content between the two cultivars. These findings are essential in enhancing our understanding of the genetic programs in both cultivars and developing novel hypotheses for further experimental studies.

Genome-wide association study reveals a patatin-like lipase relating to the reduction of seed oil content in Brassica napus

BACKGROUND

Rapeseed (Brassica napus L.) is an important oil crop world-widely cultivated, and seed oil content (SOC) is one of the most important traits for rapeseed. To increase SOC, many efforts for promoting the function of genes on lipid biosynthesis pathway have been previously made. However, seed oil formation is a dynamic balance between lipid synthesis and breakdown. It is, therefore, also reasonable to weaken or eliminate the function of genes involved in lipid degradation for a higher final SOC.

RESULTS

We applied a genome-wide association study (GWAS) on SOC in a collection of 290 core germplasm accessions. A total of 2,705,480 high-quality SNPs were used in the GWAS, and we identified BnaC07g30920D, a patatin-like lipase (PTL) gene, that was associated with SOC. In particular, six single-nucleotide-polymorphisms (SNPs) in the promoter region of BnaC07g30920D were associated with the significant reduction of SOC, leading to a 4.7-6.2% reduction of SOCs. We performed in silico analysis to show a total of 40 PTLs, which were divided into four clades, evenly distributed on the A and C subgenomes of Brassica napus. RNA-seq analysis unveiled that BnPTLs were preferentially expressed in reproductive tissues especially maturing seeds.

CONCLUSIONS

We identified BnaC07g30920D, a BnPTL gene, that was associated with SOC using GWAS and performed in silico analysis of 40 PTLs in Brassica napus. The results enrich our knowledge about the SOC formation in rapeseed and facilitate the future study in functional characterization of BnPTL genes.

Proteomic Analysis of Lipid Droplets in Sesamum indicum

We attempted to identify the total proteome in sesame lipid droplets. Results from two-dimensional electrophoresis showed 139 protein spots in lipid droplet samples. Each spot was isolated, digested with trypsin, and applied to liquid chromatography–tandem mass spectrometry (Q-Tof Premier). As a result, 103 spots were identified. Although oleosin, caleosin, and steroleosin are known major components of the lipid droplet, many other proteins were also found in the lipid droplet. In addition to the three major proteins, TAG factor protein, glyceraldehyde-3-phosphate dehydrogenase, F₁ ATPase, 70-kDa heat shock protein, seed maturation protein PM24, and 11S globulin precursor isoforms 3 and 4 were found in the lipid droplet. Three types of oleosins, 15-, 15.5-, and 17-kDa were present in the sesame lipid droplet, and the 15.5-kDa oleosin had high homology with oleosin from Coffea canephora. It has been shown by acid phosphatase treatment that oleosin proteins contain phosphate groups. Protein disulfide-isomerase 2 precursor, calreticulin-1, and BiP, which are known as marker proteins of the endoplasmic reticulum, were found as the components of the lipid droplet. Immunoconfocal microscopy was used to show that 11S globulin precursor isoform 3 and 4 were indeed localized in the lipid droplet. The presence of 11S globulin in the lipid droplets suggested a new mechanism for the lipid droplet formation.

Comparative Transcriptome Analysis of Developing Seeds and Silique Wall Reveals Dynamic Transcription Networks for Effective Oil Production in Brassica napus L

Vegetable oil is an essential constituent of the human diet and renewable raw material for industrial applications. Enhancing oil production by increasing seed oil content in oil crops is the most viable, environmentally friendly, and sustainable approach to meet the continuous demand for the supply of vegetable oil globally. An in-depth understanding of the gene networks involved in oil biosynthesis during seed development is a prerequisite for breeding high-oil-content varieties. Rapeseed (Brassica napus) is one of the most important oil crops cultivated on multiple continents, contributing more than 15% of the world’s edible oil supply. To understand the phasic nature of oil biosynthesis and the dynamic regulation of key pathways for effective oil accumulation in B. napus, comparative transcriptomic profiling was performed with developing seeds and silique wall (SW) tissues of two contrasting inbred lines with ~13% difference in seed oil content. Differentially expressed genes (DEGs) between high- and low-oil content lines were identified across six key developmental stages, and gene enrichment analysis revealed that genes related to photosynthesis, metabolism, carbohydrates, lipids, phytohormones, transporters, and triacylglycerol and fatty acid synthesis tended to be upregulated in the high-oil-content line. Differentially regulated DEG patterns were revealed for the control of metabolite and photosynthate production in SW and oil biosynthesis and accumulation in seeds. Quantitative assays of carbohydrates and hormones during seed development together with gene expression profiling of relevant pathways revealed their fundamental effects on effective oil accumulation. Our results thus provide insights into the molecular basis of high seed oil content (SOC) and a new direction for developing high-SOC rapeseed and other oil crops.

Comparative Transcriptomic Analysis of Two Brassica napus Near-Isogenic Lines Reveals a Network of Genes That Influences Seed Oil Accumulation

Rapeseed (Brassica napus) is an important oil seed crop, providing more than 13% of the world's supply of edible oils. An in-depth knowledge of the gene network involved in biosynthesis and accumulation of seed oil is critical for the improvement of B. napus. Using available genomic and transcriptomic resources, we identified 1,750 acyl-lipid metabolism (ALM) genes that are distributed over 19 chromosomes in the B. napus genome. B. rapa and B. oleracea, two diploid progenitors of B. napus, contributed almost equally to the ALM genes. Genome collinearity analysis demonstrated that the majority of the ALM genes have arisen due to genome duplication or segmental duplication events. In addition, we profiled the expression patterns of the ALM genes in four different developmental stages. Furthermore, we developed two B. napus near isogenic lines (NILs). The high oil NIL, YC13-559, accumulates significantly higher (∼10%) seed oil compared to the other, YC13-554. Comparative gene expression analysis revealed upregulation of lipid biosynthesis-related regulatory genes in YC13-559, including SHOOTMERISTEMLESS, LEAFY COTYLEDON 1 (LEC1), LEC2, FUSCA3, ABSCISIC ACID INSENSITIVE 3 (ABI3), ABI4, ABI5, and WRINKLED1, as well as structural genes, such as ACETYL-CoA CARBOXYLASE, ACYL-CoA DIACYLGLYCEROL ACYLTRANSFERASE, and LONG-CHAIN ACYL-CoA SYNTHETASES. We observed that several genes related to the phytohormones, gibberellins, jasmonate, and indole acetic acid, were differentially expressed in the NILs. Our findings provide a broad account of the numbers, distribution, and expression profiles of acyl-lipid metabolism genes, as well as gene networks that potentially control oil accumulation in B. napus seeds. The upregulation of key regulatory and structural genes related to lipid biosynthesis likely plays a major role for the increased seed oil in YC13-559.

Estructura del cotiledón de la semilla de almendra (Prunus amygdalus L.) cruda, remoj ada y tostada / Cotyledon structure of raw, soaked and roasted almond (Prunus amygdalus L.)

The microstructure of the sweet almond (variety Marcona) and the most important microstruc tural changes caused after roasting (150 °C, 45 min) and soaking (H2O and NaCl 5%, 24 h) were studied by scanning electron microscopy (SEM). The majority of the cotyledon tissue is made up of rather large, nearly isodiametric parenchyma cells with a thick cell wall; the cell-to-cell junc tions are characterized by a distinct middle lamella. The cytoplasmatic membrane delimits the cellular content, protein bodies and lipid bodies being the major components. A cytoplasmic network consisting of the membranous system structured as hexagonal cells extends throughout each parenchyma cell, and surrounds the major components. The parenchymatic tissue is surrounded by a layer of epidermic cells and tegument. After roasting, the cellular organization is lost and the cytoplasmic network surrounding the lipid bodies and protein bodies is altered; the heat destroys some middle lamellae of cell-to-cell junctions; the cytoplasmic compartimental ization of the oil is lost in most cells and the oil drops coalesce; protein bodies are distended and aggregated; other thermal modifications of roasting included pitting and pock-marking of the epidermis and protein bodies, caused by the escape of steam and oil. Soaking in water did not cause drastic changes in the structure; the most significant modification was an alteration of the cytoplasmic network and membrane; soaking in 5% NaCl also produced a partial disolution of protein bodies.

Production of a Brassica napus Low-Molecular Mass Acyl-Coenzyme A-Binding Protein in Arabidopsis Alters the Acyl-Coenzyme A Pool and Acyl Composition of Oil in Seeds

Low-molecular mass (10 kD) cytosolic acyl-coenzyme A-binding protein (ACBP) has a substantial influence over fatty acid (FA) composition in oilseeds, possibly via an effect on the partitioning of acyl groups between elongation and desaturation pathways. Previously, we demonstrated that the expression of a Brassica napus ACBP (BnACBP) complementary DNA in the developing seeds of Arabidopsis (Arabidopsis thaliana) resulted in increased levels of polyunsaturated FAs at the expense of eicosenoic acid (20:1^cisΔ11) and saturated FAs in seed oil. In this study, we investigated whether alterations in the FA composition of seed oil at maturity were correlated with changes in the acyl-coenzyme A (CoA) pool in developing seeds of transgenic Arabidopsis expressing BnACBP. Our results indicated that both the acyl-CoA pool and seed oil of transgenic Arabidopsis lines expressing cytosolic BnACBP exhibited relative increases in linoleic acid (18:2^cisΔ9,12; 17.9%-44.4% and 7%-13.2%, respectively) and decreases in 20:1^cisΔ11 (38.7%-60.7% and 13.8%-16.3%, respectively). However, alterations in the FA composition of the acyl-CoA pool did not always correlate with those seen in the seed oil. In addition, we found that targeting of BnACBP to the endoplasmic reticulum resulted in FA compositional changes that were similar to those seen in lines expressing cytosolic BnACBP, with the most prominent exception being a relative reduction in α-linolenic acid (18:3^cisΔ9,12,15) in both the acyl-CoA pool and seed oil of the former (48.4%-48.9% and 5.3%-10.4%, respectively). Overall, these data support the role of ACBP in acyl trafficking in developing seeds and validate its use as a biotechnological tool for modifying the FA composition of seed oil.

Predictive modeling of biomass component tradeoffs in Brassica napus developing oilseeds based on in silico manipulation of storage metabolism

Seed oil content is a key agronomical trait, while the control of carbon allocation into different seed storage compounds is still poorly understood and hard to manipulate. Using bna572, a large-scale model of cellular metabolism in developing embryos of rapeseed (Brassica napus) oilseeds, we present an in silico approach for the analysis of carbon allocation into seed storage products. Optimal metabolic flux states were obtained by flux variability analysis based on minimization of the uptakes of substrates in the natural environment of the embryo. For a typical embryo biomass composition, flux sensitivities to changes in different storage components were derived. Upper and lower flux bounds of each reaction were categorized as oil or protein responsive. Among the most oil-responsive reactions were glycolytic reactions, while reactions related to mitochondrial ATP production were most protein responsive. To assess different biomass compositions, a tradeoff between the fractions of oil and protein was simulated. Based on flux-bound discontinuities and shadow prices along the tradeoff, three main metabolic phases with distinct pathway usage were identified. Transitions between the phases can be related to changing modes of the tricarboxylic acid cycle, reorganizing the usage of organic carbon and nitrogen sources for protein synthesis and acetyl-coenzyme A for cytosol-localized fatty acid elongation. The phase close to equal oil and protein fractions included an unexpected pathway bypassing α-ketoglutarate-oxidizing steps in the tricarboxylic acid cycle. The in vivo relevance of the findings is discussed based on literature on seed storage metabolism.

Lipid body biogenesis and the role of microtubules in lipid synthesis in Ornithogalum umbellatum lipotubuloids

Lipid bodies present in lipotubuloids of Ornithogalum umbellatum ovary epidermis take the form of a lens between leaflets of ER (endoplasmic reticulum) membrane filled with a highly osmiophilic substance. The two enzymes, DGAT1 [DAG (diacylglycerol) acyltransferase 1] and DGAT2 (DAG acyltransferase 2), involved in this process are synthesized on rough ER and localized in the ER near a monolayer surrounding entities like lipid bodies. After reaching the appropriate size, newly formed lipid bodies transform into mature spherical lipid bodies filled with less osmiophilic content. They appear to be surrounded by a half-unit membrane, with numerous microtubules running adjacently in different directions. The ER, no longer continuous with lipid bodies, makes contact with them through microtubules. At this stage, lipid synthesis takes place at the periphery of lipid bodies. This presumption, and a hypothesis that microtubules are involved in lipid synthesis delivering necessary components to lipid bodies, is based on strong arguments: (i) silver grains first appear over microtubules after a short [3H]palmitic acid incubation and before they are observed over lipid bodies; (ii) blockade of [3H]palmitic acid incorporation into lipotubuloids by propyzamide, an inhibitor of microtubule function; and (iii) the presence of gold grains above the microtubules after DGAT1 and DGAT2 reactions, as also near microtubules after an immunogold method that identifies phospholipase D1.

Oil body proteins sequentially accumulate throughout seed development in Brassica napus

Despite the importance of seed oil bodies (OBs) as enclosed compartments for oil storage, little is known about lipid and protein accumulation in OBs during seed formation. OBs from rapeseed (Brassica napus) consist of a triacylglycerol (TAG) core surrounded by a phospholipid monolayer embedded with integral proteins which confer high stability to OBs in the mature dry seed. In the present study, we investigated lipid and protein accumulation patterns throughout seed development (from 5 to 65 days after pollination [DAP]) both in the whole seed and in purified OBs. Deposition of the major proteins (oleosins, caleosins and steroleosins) into OBs was assessed through (i) gene expression pattern, (ii) proteomics analysis, and (iii) protein immunodetection. For the first time, a sequential deposition of integral OB proteins was established. Accumulation of oleosins and caleosins was observed starting from early stages of seed development (12-17 DAP), while steroleosins accumulated later (~25 DAP) onwards.

Plant lipids: metabolism, mutants, and membranes

The mechanisms that regulate plant lipid metabolism determine the dietary and industrial value of storage oils found in economically important species and may control the ability of many plants to survive exposure to temperature extremes. Many of the problems researchers have in defining the pathways, enzymes, and genes involved in plant lipid metabolism appear to be amenable to analysis by genetic approaches. Mutants with alterations in membrane lipid composition have also been used to study the structural and adaptive roles of lipids. The application of genetic engineering methods affords opportunities for researchers to apply knowledge gained about plant lipid metabolism toward enhanced use of plant oils as abundant and renewable sources of reduced carbon.

Oil body biogenesis during Brassica napus embryogenesis

Although the oil body is known to be an important membrane enclosed compartment for oil storage in seeds, we have little understanding about its biogenesis during embryogenesis. In the present study we investigated the oil body emergence and variations in Brassica napus cv. Topas. The results demonstrate that the oil bodies could be detected already at the heart stage, at the same time as the embryos began to turn green, and the starch grains accumulated in the chloroplast stroma. In comparison, we have studied the development of oil bodies between Arabidopsis thaliana wild type (Col) and the low-seed-oil mutant wrinkled1-3. We observed that the oil body development in the embryos of Col is similar to that of B. napus cv. Topas, and that the size of the oil bodies was obviously smaller in the embryos of wrinkled1-3. Our results suggest that the oil body biogenesis might be coupled with the embryo chloroplast.

Increasing the flow of carbon into seed oil

The demand for vegetable oils for food, fuel (bio-diesel) and bio-product applications is increasing rapidly. In Canada alone, it is estimated that a 50 to 75% increase in canola oil production will be required to meet the demand for seed oil in the next 7-10years. Plant breeding and genetics have demonstrated that seed oil content is a quantitative trait based on a number of contributing factors including embryo genetic effects, cytoplasmic effects, maternal genetic effects, and genotype-environment interactions. Despite the involvement of numerous quantitative trait loci in determining seed oil content, genetic engineering to over-express/repress specific genes encoding enzymes and other proteins involved in the flow of carbon into seed oil has led to the development of transgenic lines with significant increases in seed oil content. Proteins encoded by these genes include enzymes catalyzing the production of building blocks for oil assembly, enzymes involved in oil assembly, enzymes regulating metabolic carbon partitioning between oil, carbohydrate and secondary metabolite fractions, and transcription factors which orchestrate metabolism at a more general level.

Gene expression during seed maturation in Brassica napus in relation to the induction of secondary dormancy

Gene expression in two cultivars of Brassica napus (AC Excel and DH12075) has been compared at the full-size embryo, desiccation, and mature stages of seed development. Seed of these cultivars differ in their potential to exhibit secondary dormancy following environmental stress; Excel has high potential and DH12075 has low potential. A majority of genes were down-regulated during maturation in both cultivars but a significant number of differences in gene expression between the cultivars were apparent in the transition from full-size embryo to mature seed. However, most differences were apparent in the desiccation stage and some of the differences were in genes related to signaling processes and protein biosynthesis. We suggest that the propensity of Brassica seeds to manifest secondary dormancy may be determined by changes in gene expression that occur during late seed development.

Diacylglycerol acyltransferase: A key mediator of plant triacylglycerol synthesis

Many plants deposit TAG in seeds and fruits as the major form of storage lipid. TAG production is of tremendous socioeconomic value in food, nutraceutical, and industrial applications, and thus numerous conventional and molecular genetic strategies have been explored in attempts to increase TAG content and modify the FA composition of plant seed oils. Much research has focused on the acyl-CoA-dependent reaction catalyzed by diacylglycerol acyltransferase (DGAT), which is an integral endoplasmic reticulum protein and has also been shown to be present in oil bodies and plastids. DGAT enzymes exhibit diverse biochemical properties among different plant species, many of which are summarized here. In addition to catalyzing a critical step in TAG biosynthesis, there is evidence that DGAT has roles in lipid metabolism associated with germination and leaf senescence. TAG can also be formed in plants via two different acyl-CoA-independent pathways, catalyzed by phospholipid: diacylglycerol acyltransferase and diacylglycerol transacylase. The current understanding of the terminal step in TAG formation in plants and the development of molecular genetic approaches aimed at altering TAG yield and FA composition of TAG are discussed.

Large Scale Identification and Quantitative Profiling of Phosphoproteins Expressed during Seed Filling in Oilseed Rape

Seed filling is a dynamic, temporally regulated phase of seed development that determines the composition of storage reserves in mature seeds. Although the metabolic pathways responsible for storage reserve synthesis such as carbohydrates, oils, and proteins are known, little is known about their regulation. Protein phosphorylation is a ubiquitous form of regulation that influences many aspects of dynamic cellular behavior in plant biology. Here a systematic study has been conducted on five sequential stages (2, 3, 4, 5, and 6 weeks after flowering) of seed development in oilseed rape (Brassica napus L. Reston) to survey the presence and dynamics of phosphoproteins. High resolution two-dimensional gel electrophoresis in combination with a phosphoprotein-specific Pro-Q Diamond phosphoprotein fluorescence stain revealed approximately 300 phosphoprotein spots. Of these, quantitative expression profiles for 234 high quality spots were established, and hierarchical cluster analyses revealed the occurrence of six principal expression trends during seed filling. The identity of 103 spots was determined using LC-MS/MS. The identified spots represented 70 non-redundant phosphoproteins belonging to 10 major functional categories including energy, metabolism, protein destination, and signal transduction. Furthermore phosphorylation within 16 non-redundant phosphoproteins was verified by mapping the phosphorylation sites by LC-MS/MS. Although one of these sites was postulated previously, the remaining sites have not yet been reported in plants. Phosphoprotein data were assembled into a web database. Together this study provides evidence for the presence of a large number of functionally diverse phosphoproteins, including global regulatory factors like 14-3-3 proteins, within developing B. napus seed.

Protein and lipid composition analysis of oil bodies from twoBrassica napus cultivars

Oil bodies were purified from mature seed of two Brassica napus crop cultivars, Reston and Westar. Purified oil body proteins were subjected to both 2-DE followed by LC-MS/MS and multidimensional protein identification technology. Besides previously known oil body proteins oleosin, putative embryo specific protein ATS1, (similar to caleosin), and 11-beta-hydroxysteroid dehydrogenase-like protein (steroleosin), several new proteins were identified in this study. One of the identified proteins, a short chain dehydrogenase/reductase, is similar to a triacylglycerol-associated factor from narrow-leafed lupin while the other, a protein annotated as a myrosinase associated protein, shows high similarity to the lipase/hydrolase family of enzymes with GDSL-motifs. These similarities suggest these two proteins could be involved in oil body degradation. Detailed analysis of the two other oil body components, polar lipids (lipid monolayer) and neutral lipids (triacylglycerol matrix) was also performed. Major differences were observed in the fatty acid composition of polar lipid fractions between the two B. napus cultivars. Neutral lipid composition confirmed erucic acid and oleic acid accumulation in Reston and Westar seed oil, respectively.

Proteomic analysis of seed filling in Brassica napus. Developmental characterization of metabolic isozymes using high-resolution two-dimensional gel electrophoresis

Brassica napus (cultivar Reston) seed proteins were analyzed at 2, 3, 4, 5, and 6 weeks after flowering in biological quadruplicate using two-dimensional gel electrophoresis. Developmental expression profiles for 794 protein spot groups were established and hierarchical cluster analysis revealed 12 different expression trends. Tryptic peptides from each spot group were analyzed in duplicate using matrix-assisted laser desorption ionization time-of-flight mass spectrometry and liquid chromatography-tandem mass spectrometry. The identity of 517 spot groups was determined, representing 289 nonredundant proteins. These proteins were classified into 14 functional categories based upon the Arabidopsis (Arabidopsis thaliana) genome classification scheme. Energy and metabolism related proteins were highly represented in developing seed, accounting for 24.3% and 16.8% of the total proteins, respectively. Analysis of subclasses within the metabolism group revealed coordinated expression during seed filling. The influence of prominently expressed seed storage proteins on relative quantification data is discussed and an in silico subtraction method is presented. The preponderance of energy and metabolic proteins detected in this study provides an in-depth proteomic view on carbon assimilation in B. napus seed. These data suggest that sugar mobilization from glucose to acetyl-coenzyme A [corrected] is a collaboration between the cytosol and plastids and that temporal control of enzymes and pathways extends beyond transcription. This study provides a systematic analysis of metabolic processes operating in developing B. napus seed from the perspective of protein expression. Data generated from this study have been deposited into a web database (http://oilseedproteomics.missouri.edu) that is accessible to the public domain.

Expression of the FAE1 gene and FAE1 promoter activity in developing seeds of Arabidopsis thaliana

Plant fatty acid elongase which catalyzes very-long-chain fatty acid (VLCFA) biosynthesis is a membrane-bound multienzyme complex. It is composed of four enzymes, a 3-ketoacyl-CoA synthase (condensing enzyme), a 3-ketoacyl-CoA reductase, a 3-hydroxyacyl-CoA dehydrase, and an enoyl-CoA reductase required for completion of each step of 2-carbon elongation of fatty acids. To improve our understanding of the overall regulation of the fatty acid elongase, we investigated the spatial and temporal expression of its key component, the FAE1-condensing enzyme, and examined the activity of the promoter of the FAE1 gene in Arabidopsis. In situ hybridization results revealed that FAE1 transcripts were found exclusively in the embryo. RNA blot analysis and histochemical analysis of GUS activity in pFAE1::GUS transgenic Arabidopsis lines demonstrated that the FAE1 gene was already transcribed in the early torpedo stage embryos 4-5 days after flowering, with transcription reaching its peak 9-11 days after flowering. VLCFA deposition closely paralleled FAE1 transcript accumulation. FAE1 promoter was highly active and embryo-specific. Because its timing coincides with the period of major storage lipid accumulation, and because its in vivo activity in Arabidopsis is superior to the napin promoter, FAE1 promoter may be ideal for genetic engineering of seed oil composition.

Oil bodies and their associated proteins, oleosin and caleosin

Oil bodies are lipid storage organelles which have been analyzed biochemically due to the economic importance of oil seeds. Although oil bodies are structurally simple, the mechanisms involved in their formation and degradation remain controversial. At present, only two proteins associated with oil bodies have been described, oleosin and caleosin. Oleosin is thought to be important for oil body stabilization in the cytosol, although neither the structure nor the function of oleosin has been fully elucidated. Even less is known about caleosin, which has only recently been described [Chen et al. (1999) Plant Cell Physiol 40: 1079-1086; Naested et al. (2000) Plant Mol Biol 44: 463-476]. Caleosin and caleosin-like proteins are not unique to oil bodies and are associated with an endoplasmatic reticulum subdomain in some cell types. Here we review the synthesis and degradation of oil bodies as they relate to structural and functional aspects of oleosin and caleosin.

Two new oleosin isoforms with altered expression patterns in seeds of the Arabidopsis mutant fus3

Oleosins are proteins associated with lipid bodies mainly synthesised during seed development. Using a subtractive hybridisation approach two new members of the oleosin gene family of Arabidopsis thaliana have been isolated. The quantitative and temporal expression patterns of both genes are found to be affected in the fus3 mutant defective in late embryogenesis. This pattern is interpreted as a molecular marker for a mutant specific developmental change from a seed maturation to a germination pathway.

Production of biologically active hirudin in plant seeds using oleosin partitioning

A plant oleosin was used as a 'carrier' for the production of the leech anticoagulant protein, hirudin (variant 2). The oleosin-hirudin fusion protein was expressed and accumulated in seeds. Seed-specific expression of the oleosin-hirudin fusion mRNA was directed via an Arabidopsis oleosin promoter. The fusion protein was correctly targeted to the oil body membrane and separated from the majority of other seed proteins by flotation centrifugation. Recombinant hirudin was localized to the surface of oil bodies as determined by immunofluorescent techniques. The oleosin-hirudin fusion protein accumulated to ca. 1% of the total seed protein. Hirudin was released from the surface of the oil bodies using endoprotease treatment. Recombinant hirudin was partially purified through anion exchange chromatography and reverse-phase chromatography. Hirudin activity, measured in anti-thrombin units (ATU), was observed in seed oil body extracts, but only after the proteolytic release of hirudin from its oleosin 'carrier'. About 0.55 ATU per milligram of oil body protein was detected in cleaved oil body preparations. This activity demonstrated linear dose dependence. The oleosin fusion protein system provides a unique route for the large-scale production of recombinant proteins in plants, as well as an efficient process for purification of the desired polypeptide.

Expression and in vitro targeting of a sunflower oleosin

Two distinct cDNAs encoding oleosins (oil body proteins) have been identified by degenerate PCR as transcripts present in the developing seeds of sunflower (Helianthus annuus L. cv. Dwarf Sunbred). One (pSOM) of these is closely related to a reported sunflower oleosin, whilst the other (pSO5) has not been previously described. Different expression patterns were observed for the two cDNAs, pSO5 being expressed earlier than pSOM in seed maturation and oil deposition. The results support the contention that oleosin proteins are synthesised either during or closely after the formation of the oil body. Translation in vitro of synthetic oleosin transcripts was enhanced by the addition of microsomes but suppressed by the addition of purified signal recognition particle (SRP) complex. Deletion of 62 amino acid residues at the C-terminus of the oleosin did not alter the in vitro targeting of the protein to the microsomal membrane. Taken together these data support the idea that oleosins are targeted to the ER membrane as part of oil body biogenesis.

Plant seed oil-bodies as carriers for foreign proteins

Plant seeds frequently store oils (triglycerides) in discrete organelles called oil-bodies. These are normally surrounded by a phospholipid half-unit membrane equipped with specialized proteins called oleosins. Oleosins are highly lipophilic proteins, are expressed at high levels in many seeds and are specifically targeted to oil-bodies. We have investigated the potential of oleosins to act as carriers for recombinant proteins by the production of translational fusions between oleosins and genes encoding proteins foreign to plant cells. We have shown that a fusion comprising a complete oleosin coding domain and a beta-glucuronidase coding sequence may be expressed specifically in the seeds of the oilseed crop plant, Brassica napus, and its product is correctly targeted with approximately 80% of the activity partitioning with oil-bodies. Recombinant oil-bodies may be used to facilitate separation of a recombinant protein from other cellular proteins. Using this approach, the desired protein may be cleaved from the oil-bodies using an endoprotease and further purified. Alternatively, a fusion protein which is enzymatically active and resides on the oil-bodies may be used directly in heterogeneous catalysis. In this application, after a round of catalysis the oil-bodies may be recovered and re-used several times without loss of activity. Thus the oil-bodies act as an immobilization matrix. The fusion protein is stable in dry seeds for long periods and when extracted has a half-life of 3-4 weeks on oil-bodies. Finally, the production of these recombinant oil-bodies is extremely inexpensive, offering a novel route to the manufacture of recombinant proteins.

Spin label EPR study of lipid solvation of supramolecular photosynthetic protein complexes in thylakoids

Lipid-protein association in the chloroplast membrane and its various thylakoid fractions from higher plants, namely pea and maize, rich in Photosystem I (PSI) and Photosystem II (PSII), respectively, were studied using EPR spectroscopy of spin-labelled lipid molecules. All the EPR spectra consisted of two spectral components corresponding to bulk fluid lipids and solvation lipids motionally restricted at the hydrophobic surface of membrane proteins. Spin-labelled stearic acid and phosphatidylglycerol exhibited marked selectivity towards the supramolecular protein complexes of both PSI and PSII although to different extent. In addition, lipid-protein titration experiments are described for partially delipidated PSII-enriched membrane fractions of pea chloroplasts, incorporating unlabelled egg phosphatidylcholine prior to or after the incorporation of spin-labelled lipids. Two sets of solvation sites were resolved by timed labelling experiments and a significant result of these studies was that a well-defined population of solvation sites (approx. 100 mol lipids/820 kDa protein) was rapidly exchanged by laterally diffusing membrane lipids, while other solvation sites (approx. 50 mol lipids/820 kDa protein) were exchanged much slower or not exchanged at all.

Regulation of an Arabidopsis oleosin gene promoter in transgenic Brassica napus

Progressive deletions of the 5'-flanking sequences of an Arabidopsis oleosin gene were fused to beta-glucuronidase (GUS) and introduced into Brassica napus plants using Agrobacterium-mediated transformation. The effect of these deletions on the quantitative level of gene expression, organ specificity and developmental regulation was assessed. In addition, the influence of abscisic acid (ABA), jasmonic acid (JA), sorbitol and a combined ABA/sorbitol treatment on gene expression was investigated. Sequences that positively regulate quantitative levels of gene expression are present between -1100 to -600 and -400 to -200 of the promoter. In addition, sequences present between -600 and -400 down-regulate quantitative levels of expression. In transgenic B. napus plants, the oleosin promoter directs seed-specific expression of GUS which is present at early stages of seed development and increases throughout seed maturation. Sequences present between -2500 and -1100 of the promoter are involved in modulating the levels of expression at early stages of embryo development. Histochemical staining of embryos demonstrated that expression is uniform throughout the tissues of the embryo. Sequences involved in the response to ABA and sorbitol are present between -400 and -200. The induction of GUS activity by a combined ABA/sorbitol treatment is additive suggesting that ABA is not the sole mediator of osmotically induced oleosin gene expression. A response to JA was only observed when the oleosin promoter was truncated to -600 suggesting that the reported effect of JA on oleosin gene expression may be at a post-transcriptional level.

Differential, temporal and spatial expression of genes involved in storage oil and oleosin accumulation in developing rapeseed embryos: implications for the role of oleosins and the mechanisms of oil-body formation

The temporal and spatial expression of oleosin and delta 9-stearoyl-ACP desaturase genes and their products has been examined in developing embryos of rapeseed, Brassica napus L. var. Topas. Expression of oleosin and stearate desaturase genes was measured by in situ hybridisation at five different stages of development ranging from the torpedo stage to a mature-desiccating embryo. The temporal pattern of gene expression varied dramatically between the two classes of gene. Stearate desaturase gene expression was relatively high, even at the torpedo stage, whereas oleosin gene expression was barely detectable at this stage. By the stage of maximum embryo fresh weight, stearate desaturase gene expression had declined considerably while oleosin gene expression was at its height. In contrast to their differential temporal expression, the in situ labelling of both classes of embryo-specific gene showed similar, relatively uniform patterns of spatial expression throughout the embryo sections. Immunogold labelling of ultra-thin sections from radicle tissue with anti-oleosin antibodies showed similar patterns to sections from cotyledon tissue. However, whereas at least three oleosin isoforms were detectable on western blots of homogenates from cotyledons, only one isoform was found in radicles. This suggests that some of the oleosin isoforms may be expressed differentially in the various types of embryo tissue. The differential timing of stearate desaturase and oleosin gene expression was mirrored by similar differences in the timing of the accumulation of their ultimate products, i.e. storage oil and oleosin proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipids, Proteins, and Structure of Seed Oil Bodies from Diverse Species

Oil bodies isolated from the mature seeds of rape (Brassica napus L.), mustard (Brassica juncea L.), cotton (Gossypium hirsutum L.), flax (Linus usitatis simum), maize (Zea mays L.), peanut (Arachis hypogaea L.), and sesame (Sesamum indicum L.) had average diameters that were different but within a narrow range (0.6-2.0 [mu]m), as measured from electron micrographs of serial sections. Their contents of triacylglycerols (TAG), phospholipids, and proteins (oleosins) were correlated with their sizes. The correlation fits a formula that describes a spherical particle surrounded by a shell of a monolayer of phospholipids embedded with oleosins. Oil bodies from the various species contained substantial amounts of the uncommon negatively charged phosphatidylserine and phosphatidylinositol, as well as small amounts of free fatty acids. These acidic lipids are assumed to interact with the basic amino acid residues of the oleosins on the surface of the phospholipid layer. Isoelectrofocusing revealed that the oil bodies from the various species had an isoelectric point of 5.7 to 6.6 and thus possessed a negatively charged surface at neutral pH. We conclude that seed oil bodies from diverse species are very similar in structure. In rapeseed during maturation, TAG and oleosins accumulated concomitantly. TAG-synthesizing acyltransferase activities appeared at an earlier stage and peaked during the active period of TAG accumulation. The concomitant accumulation of TAG and oleosins is similar to that reported earlier for maize and soybean, and the finding has an implication for the mode of oil body synthesis during seed maturation.

Oilbody Proteins in Microspore-Derived Embryos of Brassica napus: Hormonal, Osmotic, and Developmental Regulation of Synthesis

A number of treatments were tested for their ability to affect the synthesis of oilbody proteins in microspore-derived embryos of rapeseed (Brassica napus). Synthesis of the oilbody proteins was determined by [(35)S]methionine incorporation in vivo and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of washed oilbody fractions. Oilbody proteins of approximately 19, 23, and 32 kilodaltons were found to be prominent. These proteins showed differential patterns of regulation. The 19 and 23 kilodalton proteins (oleosins) were greatly enhanced by treatments with abscisic acid, jasmonic acid, and osmotic stress imposed using sorbitol (12.5%). Synthesis of the 32 kilodalton protein was inhibited by abscisic acid and by sorbitol (12.5%), but unaffected by jasmonates. The strong promotion of synthesis of the 19 and 23 kilodalton oilbody proteins appeared to be specific as they are not seen with gibberellic acid treatment or with a stress such as heat shock. Time course experiments revealed that the abscisic acid stimulation of oleosin synthesis is quite rapid (less than 2 hours), reaching a maximum at 6 to 8 hours. The response of the oleosins to abscisic acid is found in all stages of embryogenesis, with a major increase in synthetic rates even in globular embryos on abscisic acid treatment. This suggests that these proteins may accumulate much earlier in embryogenesis than has previously been believed. The 32 kilodalton oilbody-associated protein appears different from the oleosins in several ways, including its distinct pattern of regulation and its unique property, among the oilbody proteins, of undergoing phosphorylation.

Maize oleosin is correctly targeted to seed oil bodies in Brassica napus transformed with the maize oleosin gene

Oleosins are small hydrophobic abundant proteins localized in the oil bodies of plant seeds. An oleosin gene from the monocotyledonous maize (Zea mays L.) was transferred into the dicotyledonous Brassica napus L. using Agrobacterium-mediated transformation. The maize oleosin gene was placed under the control of either its own promoter/terminator or the promoter/terminator of a Brassica seed storage protein (napin) gene. Southern blot analyses of individual transformed plants suggested that the oleosin gene from either construct was incorporated into the Brassica chromosomes without appreciable structural alterations. The amount of construct incorporated was from 1 to >10 copies per haploid genome, depending on the individual transformant. Maize oleosin mRNA and protein were detected only in the transformants containing the napin gene promoter/terminator constructs; these transformants were studied further. Northern blot analyses of RNA isolated from different tissues and seeds of different developmental stages indicated that the maize oleosin mRNA was present only in the maturing seed. Approximately 1% of the total protein in mature seed was represented by maize oleosin. Subcellular fractionation of the mature seed revealed that 90% or more of the maize oleosin, as well as the Brassica oleosin, was localized in the oil bodies. The results show that a monocotyledonous oleosin possesses sufficient targeting information for its proper intracellular transport in a dicotyledon and also suggest that the napin gene promoter/terminator of Brassica, or equivalent seed storage protein regulatory elements of other plant species, may be used to express genes for the genetic engineering of seed oils.

Plant protein phosphatases. Subcellular distribution, detection of protein phosphatase 2C and identification of protein phosphatase 2A as the major quinate dehydrogenase phosphatase

Protein phosphatases 1 and 2A (PP1 and PP2A) were identified in a variety of plant cells and found to be particulate or soluble depending on the species. In extracts prepared from oilseed-rape seeds these enzymes were associated with microsomes and more rapidly sedimenting fractions, whereas in wheat leaf extracts they were largely microsomal, the remainder being present in the soluble fraction. In pea leaf and carrot cell extracts PP1 and PP2A were almost entirely soluble. No PP1 or PP2A activity was associated with the membranes or stroma of chloroplasts in oilseed-rape seeds, pea leaves and wheat leaves. An Mg2(+)-dependent okadaic acid-insensitive protein phosphatase that resembles protein phosphatase 2C (PP2C) was detected in carrot cells, pea leaves and wheat leaves, but not in oilseed-rape seeds. In wheat leaf extracts PP2C was mostly present in the soluble fraction, a different location from PP1 or PP2A. The rapid inactivation of the cytosolic enzyme quinate dehydrogenase (QDH) in a fraction prepared from light-grown carrot cells was completely blocked by either okadaic acid or microcystin (two potent and specific inhibitors of PP1 and PP2A), whereas inhibitor 2 (a specific inhibitor of PP1) inhibited inactivation by only about 10%. Addition of the purified PP2A catalytic subunit from mammalian skeletal muscle increased the rate of QDH inactivation, whereas addition of mammalian PP1 did not. It is concluded that PP2A is the major enzyme responsible for dephosphorylating (inactivating) QDH in carrot cells. These observations indicate that okadaic acid and microcystin may be useful for identifying other plant processes that are controlled by phosphorylation/dephosphorylation mechanisms. Okadaic acid did not prevent the rapid inactivation of phosphoribulokinase or activation of glucose-6-phosphate dehydrogenase in a fraction prepared from light-grown pea leaves, and addition of the purified catalytic subunits of PP1 and PP2A did not accelerate either process. These observations, in conjunction with the absence of PP1 and PP2A activity in chloroplasts, suggest that these phosphatases are not involved in the regulation of chloroplast metabolism.

Effects of jasmonic Acid on embryo-specific processes in brassica and linum oilseeds

A number of effects on embryogenesis of the putative phytohormone jasmonic acid (JA), and its methyl ester (MeJA), were investigated in two oilseed plants, repeseed (Brassica napus) and flax (Linum usitatissimum). Results from treatments with JA and MeJA were compared with those of a known effector of several aspects of embryogenesis, abscisic acid (ABA). Jasmonic acid was identified by gas chromatography-mass spectrometry as a naturally occurring substance in both plant species during embryo development. Both JA and MeJA can prevent precocious germination of B. napus microspore embryos and of cultured zygotic embryos of both species at an exogenous concentration of >1 micromolar. This dose-response was comparable with results obtained with ABA. Inhibitory effects were also observed on seed germination with all three growth regulators in rapeseed and flax. A number of molecular aspects of embryogenesis were also investigated. Expression of the B. napus storage protein genes (napin and cruciferin) was induced in both microspore embryos and zygotic embryos by the addition of 10 micromolar JA. The level of napin and cruciferin mRNA detected was similar to that observed when 10 micromolar ABA was applied to these embryos. For MeJA only slight increases in napin or cruciferin mRNA were observed at concentrations of 30 micromolar. Several oilbody-associated proteins were found to accumulate when the embryos were incubated with either JA or ABA in both species. The MeJA had little effect on oilbody protein synthesis. The implications of JA acting as a natural regulator of gene expression in zygotic embryogenesis are discussed.

Apparent processing of a soybean oil body protein accompanies the onset of oil mobilization

The membrane surrounding the oil body contains several different specific polypeptides. To study the biosynthesis and posttranslational modification of these polypeptides we have prepared monoclonal antibodies against purified oil bodies of soybean (Glycine max). Three of the five monoclonals selected recognize a molecular mass 34 kilodalton protein (P34). Epitope mapping of CNBr and proteolytic fragments of P34 indicates that two of the anti-P34 monoclonal antibodies are directed at different epitopes. P34 is accumulated during seed maturation at the same time as the reserve proteins and oil. SDS/PAGE-immunoblots of germinating soybean seed cotyledons indicate that the protein is initially present as a molecular mass 34 kilodalton polypeptide and is processed to molecular mass 32 kilodalton on the fourth through sixth days of seedling growth simultaneously with the onset of oil mobilization. A comparison of reduced and carboxymethylated oil body proteins with nonreduced proteins by SDS/PAGE indicates that P34 exists in vivo as a dimer of molecular mass 58 kilodalton. Comparing the amino terminal sequences of P34 and P32 indicates that their difference is at least in part due to the removal of the amino terminus of P34. The amino terminal sequences of P34 and P32 were aligned to show that the transition of P34 to P32 was accompanied by the removal of a hydrophilic decapeptide (KKMKKEQYSC) at the amino terminus of P34. Hopp-Woods hydrophilicity analysis of the deleted amino terminus of P34 shows that it is more hydrophilic and charged than the sequence of the protein which immediately follows.

Storage-protein regulation and lipid accumulation in microspore embryos of Brassica napus L

Embryos derived in vitro from isolated microspores of Brassica napus L. were compared with their zygotic counterparts. Parameters investigated included storage-protein accumulation and gene expression, fattyacid composition, storage-lipid biosynthesis, and the appearance of oil-body proteins. The microspore embryos accumulate storage-protein and show increases in levels of their transcripts during the torpedo stage. These embryos were sensitive to abscisic acid (ABA) with respect to accumulation of storage-protein mRNA and oil-body proteins. Post-transcriptional regulation of cruciferin accumulation is indicated by a disparity between ABA-enhanced transcript accumulation and a less marked effect at the level of protein accumulation. To investigate storage-lipid profiles, two cultivars of Brassica napus, Reston and Topas, were used. The former accumulates major quantities of C20 (11.2%) and C22 (39.9%) fatty acids in its seeds, the latter predominantly C18 fatty acids. The higher-molecular-weight fatty acids (>C18) normally occur only in seeds and were used as biochemical markers for seed-specific metabolism in microspore embryos. Microspore embryos from Reston were found to accumulate C20 (10.6%) and C22 (31.2%) fatty acids after 35 d in culture at levels and proportions comparable to those found in seeds. Similarly, microspore embryos of Topas had a fatty-acid profile similar to that of mature Topas seed. Activities of enzymes involved in the accumulation of storage lipids (erucoyl-CoA synthetase [EC 6.2.1.3], erucoyl-CoA thioesterase [EC 3.1.2.2] and erucoyl-CoA acyltransferase [EC 2.3.1.15 or EC 2.3.1.20]) were detected in torpedostage microspore embryos. Their specific activities were higher than have been reported to date for analogous preparations from zygotic embryos of B. napus. The similarities in storage-lipid and protein composition of these embryos to their zygotic counterparts, along with their sensitivity to ABA, indicate that microspore embryos might be exploited to facilitate studies of biochemistry and gene regulation in oilseeds.