Biosensing with Oleosin-Stabilized Liquid Crystal Droplets

Liquid crystals (LCs) are emerging as novel platforms for chemical, physical, and biological sensing. They can be used to detect biological amphiphiles such as lipids, fatty acids, digestive surfactants, and bacterial endotoxins. However, designing LC-based sensors in a manner that preserves their sensitivity and responsiveness to these stimuli, and possibly improves biocompatibility, remains challenging. In this work, the stabilization of LC droplets by oleosins, plant-sourced and highly surface active proteins due to their extended amphipathic helix, is investigated. Purified oleosins, at sub-micromolar concentrations, are shown to readily stabilize nematic LC droplets without switching their alignment, allowing them to detect surfactants at micromolar concentrations. Direct evidence of localization of oleosins at the LC-water interface is provided with fluorescent labeling, and the stabilized droplets remain stable over months. Interestingly, chiral LC droplets readily switch in the presence of nanomolar oleosin concentrations, an unexpected behavior that is explained by accounting for the energy barriers required for switching the alignment between the two cases. This leads thus to a twofold conclusion: oleosin-stabilized nematic LC droplets present a biocompatible alternative for bioanalyte detection, while chiral LCs can be further investigated for use as highly sensitive sensors for detecting amphipathic helices in biological systems.

Identification of New Allergens in Macadamia Nut and Cross-Reactivity with Other Tree Nuts in a Spanish Cohort

The consumption of macadamia nuts has increased due to their cardioprotective and antioxidant properties. However, this rise is consistent with an increase in the cases of macadamia nut allergy, leading to severe reactions. Although two Macadamia integrifolia allergens (Mac i 1 and Mac i 2) have been identified in Australian and Japanese patients, the allergenic sensitization patterns in Western European populations, particularly in Spain, remain unclear. For this purpose, seven patients with macadamia nut allergy were recruited in Spain. Macadamia nut protein extracts were prepared and, together with hazelnut and walnut extracts, were used in Western blot and inhibition assays. IgE-reactive proteins were identified using MALDI-TOF/TOF mass spectrometry (MS). Immunoblotting assays revealed various IgE-binding proteins in macadamia nut extracts. Mass spectrometry identified three new allergens: an oleosin, a pectin acetylesterase, and an aspartyl protease. Cross-reactivity studies showed that hazelnut extract but not walnut extract inhibited macadamia nut oleosin-specific IgE binding. This suggests that oleosin could be used as marker for macadamia-hazelnut cross-reactivity. The results show an allergenic profile in the Spanish cohort different from that previously detected in Australian and Japanese populations. The distinct sensitization profiles observed highlight the potential influence of dietary habits and environmental factors exposure on allergenicity.

Polyamine depletion enhances oil body mobilization through possible regulation of oleosin degradation and aquaporin abundance on its membrane

Oil body (OB) mobilization, a crucial event associated with early seedling growth, is delayed in response to salt stress. Previous reports suggest that careful regulation of polyamine (PA) metabolism is essential for salt stress tolerance in plants. Many aspects of PA-mediated regulation of metabolism have been uncovered. However, their role in the process of OB mobilization remains unexplored. Interestingly, the present investigations reveal a possible influence of PA homeostasis on OB mobilization, while implicating complex regulation of oleosin degradation and aquaporin abundance in OB membranes in the process. Application of PA inhibitors resulted in the accumulation of smaller OBs when compared to control (-NaCl) and the salt-stressed counterparts, suggesting a faster rate of mobilization. PA deficit also resulted in reduced retention of some larger oleosins under controlled conditions but enhanced retention of all oleosins under salt stress. Additionally, with respect to aquaporins, a higher abundance of PIP2 under PA deficit both under control and saline conditions, is correlated with a faster mobilization of OBs. Contrarily, TIP1s, and TIP2s remained almost undetectable in response to PA depletion and were differentially regulated by salt stress. The present work, thus, provides novel insights into PA homeostasis-mediated regulation of OB mobilization, oleosin degradation, and aquaporin abundance on OB membranes.

Identification of Key Lipogenesis Stages and Proteins Involved in Walnut Kernel Development

Walnuts are abundant in oil content, especially for polyunsaturated fatty acids, but the understanding of their formation is limited. We collected walnut (Juglans regia L.) kernels at 60, 74, 88, 102, 116, 130, and 144 days after pollination (designated S1-S7). The ultrastructure and accumulation of oil bodies (OBs) were observed using transmission electron microscopy (TEM), and the oil content, fatty acid composition, and proteomic changes in walnut kernels were determined. The oil content and OB accumulation increased during the development and rose sharply from S1 to S3 stages, which are considered the key lipogenesis stage. A total of 5442 proteins were identified and determined as differentially expressed proteins (DEPs) using label-free proteomic analysis. Fatty acid desaturases (FAD) 2, FAD3, oleosin, and caleosin were essential and upregulated from the S1 to S3 stages. Furthermore, the highly expressed oleosin gene JrOLE14.7 from walnuts was cloned and overexpressed in transgenic Brassica napus. The overexpression of JrOLE14.7 increased the oil content, diameter, hundred weight of seeds and changed the fatty acid composition and OB size of Brassica napus seeds. These findings provide insights into the molecular mechanism of oil biosynthesis and the basis for the genetic improvement of walnuts.

Impact of processing on the oxidative stability of oil bodies

Plant lipids are stored as emulsified lipid droplets also called lipid bodies, spherosomes, oleosomes or oil bodies. Oil bodies are found in many seeds such as cereals, legumes, or in microorganisms such as microalgae, bacteria or yeast. Oil Bodies are unique subcellular organelles with sizes ranging from 0.2 to 2.5 μm and are made of a triacylglycerols hydrophobic core that is surrounded by a unique monolayer membrane made of phospholipids and anchored proteins. Due to their unique properties, in particular their resistance to coalescence and aggregation, oil bodies have an interest in food formulations as they can constitute natural emulsified systems that does not need the addition of external emulsifier. This manuscript focuses on how extraction processes and other factors impact the oxidative stability of isolated oil bodies. The potential role of oil bodies in the oxidative stability of intact foods is also discussed. In particular, we discuss how constitutive components of oil bodies membranes are associated in a strong network that may have an antioxidant effect either by physical phenomenon or by chemical reactivities. Moreover, the importance of the selected process to extract oil bodies is discussed in terms of oxidative stability of the recovered oil bodies.

Progress on the functional role of oleosin gene family in plants

Oil bodies, also known as lipid droplets or oil droplets, are important organelles for oil storage in plant cells. The oil body is composed of a monolayer of phospholipid membrane encapsulating neutral fatty acids, and a variety of membrane proteins are embedded in the membrane, including oleosin, caleosin and steroleosin, of which oleosin accounts for 80%-90%. Oleosin plays important biological roles in various biological roles, such as affecting the size and stability of oil bodies, formation and degradation of oil bodies, lipid metabolism, and seed maturation and germination. In this review, we summarize the sequence and structural characteristics of oleosin and its important role in plant growth and development based on the research progress of plant oleosin gene families at home and abroad in recent years. Additionally, we discuss the application of oleosin in actual production and problems in the research and application, in order to provide a useful reference for people to further study the functions of oleosin-related molecules and their application in production practice.

Transcriptome and Regional Association Analyses Reveal the Effects of Oleosin Genes on the Accumulation of Oil Content in Brassica napus

Rapeseed stores lipids in the form of oil bodies. Oil bodies in the seeds of higher plants are surrounded by oleosins. Adjusting oleosin protein levels can prevent the fusion of oil bodies and maintain oil body size during seed development. However, oil contents are affected by many factors, and studies on the complex molecular regulatory mechanisms underlying the variations in seed oil contents of B. napus are limited. In this study, a total of 53 BnOLEO (B. napus oleosin) genes were identified in the genome of B. napus through a genome-wide analysis. The promoter sequences of oleosin genes consisted of various light-, hormone-, and stress-related cis-acting elements, along with transcription factor (TF) binding sites, for 25 TF families in 53 BnOLEO genes. The differentially expressed oleosin genes between two high- and two low-oil-content accessions were explored. BnOLEO3-C09, BnOLEO4-A02, BnOLEO4-A09, BnOLEO2-C04, BnOLEO1-C01, and BnOLEO7-A03 showed higher expressions in the high-oil-content accessions than in low-oil-content accessions, at 25, 35, and 45 days after pollination (DAP) in two different environments. A regional association analysis of 50 re-sequenced rapeseed accessions was used to further analyze these six BnOLEO genes, and it revealed that the nucleotide variations in the BnOLEO1-C01 and BnOLEO7-A03 gene regions were related to the phenotypic variations in seed oil content. Moreover, a co-expression network analysis revealed that the BnOLEO genes were directly linked to lipid/fatty acid metabolism, TF, lipid transport, and carbohydrate genes, thus forming a molecular network involved in seed oil accumulation. These favorable haplotypes can be utilized in molecular marker-assisted selection in order to further improve seed oil contents in rapeseed.

Plant oil bodies and their membrane components: new natural materials for food applications

Plants store triacylglycerols in the form of oil bodies (OBs) as an energy source for germination and subsequent seedling growth. The interfacial biomaterials from these OBs are called OB membrane materials (OBMMs) and have several applications in foods, e.g., as emulsifiers. OBMMs are preferred, compared with their synthetic counterparts, in food applications as emulsifiers because they are natural, i.e., suitable for clean label, and may stabilize bioactive components during storage. This review focuses mainly on the extraction technologies for plant OBMMs, the functionality of these materials, and the interaction of OB membranes with other food components. Different sources of OBs are evaluated and the challenges during the extraction and use of these OBMMs for food applications are addressed.

Microbubbles Stabilized by Protein Shell: From Pioneering Ultrasound Contrast Agents to Advanced Theranostic Systems

Ultrasound is a widely-used imaging modality in clinics as a low-cost, non-invasive, non-radiative procedure allowing therapists faster decision-making. Microbubbles have been used as ultrasound contrast agents for decades, while recent attention has been attracted to consider them as stimuli-responsive drug delivery systems. Pioneering microbubbles were Albunex with a protein shell composed of human serum albumin, which entered clinical practice in 1993. However, current research expanded the set of proteins for a microbubble shell beyond albumin and applications of protein microbubbles beyond ultrasound imaging. Hence, this review summarizes all-known protein microbubbles over decades with a critical evaluation of formulations and applications to optimize the safety (low toxicity and high biocompatibility) as well as imaging efficiency. We provide a comprehensive overview of (1) proteins involved in microbubble formulation, (2) peculiarities of preparation of protein stabilized microbubbles with consideration of large-scale production, (3) key chemical factors of stabilization and functionalization of protein-shelled microbubbles, and (4) biomedical applications beyond ultrasound imaging (multimodal imaging, drug/gene delivery with attention to anticancer treatment, antibacterial activity, biosensing). Presented critical evaluation of the current state-of-the-art for protein microbubbles should focus the field on relevant strategies in microbubble formulation and application for short-term clinical translation. Thus, a protein bubble-based platform is very perspective for theranostic application in clinics.

Biogenesis and Lipase-Mediated Mobilization of Lipid Droplets in Plants

Cytosolic lipid droplets (LDs) derived from the endoplasmic reticulum (ER) mainly contain neutral lipids, such as triacylglycerols (TAGs) and sterol esters, which are considered energy reserves. The metabolic pathways associated with LDs in eukaryotic species are involved in diverse cellular functions. TAG synthesis in plants is mediated by the sequential involvement of two subcellular organelles, i.e., plastids - plant-specific organelles, which serve as the site of lipid synthesis, and the ER. TAGs and sterol esters synthesized in the ER are sequestered to form LDs through the cooperative action of several proteins, such as SEIPINs, LD-associated proteins, LDAP-interacting proteins, and plant-specific proteins such as oleosins. The integrity and stability of LDs are highly dependent on oleosins, especially in the seeds, and oleosin degradation is critical for efficient mobilization of the TAGs of plant LDs. As the TAGs mobilize in LDs during germination and post-germinative growth, a plant-specific lipase-sugar-dependent 1 (SDP1)-plays a major role, through the inter-organellar communication between the ER and peroxisomes. In this review, we briefly recapitulate the different processes involved in the biogenesis and degradation of plant LDs, followed by a discussion of future perspectives in this field.

The DROL1 subunit of U5 snRNP in the spliceosome is specifically required to splice AT-AC-type introns in Arabidopsis

An Arabidopsis mutant named defective repression of OLE3::LUC 1 (drol1) was originally isolated as a mutant with defects in the repression of OLEOSIN3 (OLE3) after seed germination. In this study, we show that DROL1 is an Arabidopsis homolog of yeast DIB1, a subunit of the U5 small nuclear ribonucleoprotein particle (snRNP) in the spliceosome. It is also part of a new subfamily that is specific to a certain class of eukaryotes. Comprehensive analysis of the intron splicing using RNA sequencing analysis of the drol1 mutants revealed that most of the minor introns with AT-AC dinucleotide termini had reduced levels of splicing. Only two nucleotide substitutions from AT-AC to GT-AG enabled AT-AC-type introns to be spliced in drol1 mutants. Forty-eight genes, including those having important roles in abiotic stress responses and cell proliferation, exhibited reduced splicing of AT-AC-type introns in the drol1 mutants. Additionally, drol1 mutant seedlings showed retarded growth, similar to that caused by the activation of abscisic acid signaling, possibly as a result of reduced AT-AC-type intron splicing in the endosomal Na⁺ /H⁺ antiporters and plant-specific histone deacetylases. These results indicate that DROL1 is specifically involved in the splicing of minor introns with AT-AC termini and that this plays an important role in plant growth and development.

Abscisic acid activation of oleosin gene HvOle3 expression prevents the coalescence of protein storage vacuoles in barley aleurone cells

Protein storage vacuoles (PSVs) in aleurone cells coalesce during germination, and this process is highly coupled with mobilization of PSV reserves, allowing de novo synthesis of various hydrolases in aleurone cells for endosperm degradation. Here we show that in barley (Hordeum vulgare L.) oleosins, the major integral proteins of oleosomes are encoded by four genes (HvOle1 to 4), and the expression of HvOle1 and HvOle3 is strongly up-regulated by abscisic acid (ABA), which shows antagonism to gibberellic acid. In aleurone cells, all HvOLEs were subcellularly targeted to the tonoplast of PSVs. Gain-of-function analyses revealed that HvOLE3 effectively delayed PSV coalescence, whereas HvOLE1 only had a moderate effect, with no notable effect of HvOLE2 and 4. With regard to longevity, HvOLE3 chiefly outperformed other HvOLEs, followed by HvOLE1. Experiments swapping the N- and C-terminal domain between HvOLE3 and other HvOLEs showed that the N-terminal region of HvOLE3 is mainly responsible, with some positive effect by the C-terminal region, for mediating the specific preventive effect of HvOLE3 on PSV coalescence. Three ACGT-core elements and the RY-motif were responsible for ABA induction of HvOle3 promoter activity. Transient expression assays using aleurone protoplasts demonstrated that transcriptional activation of the HvOle3 promoter was mediated by transcription factors HvABI3 and HvABI5, which acted downstream of protein kinase HvPKABA1.

Identification of a Novel Major Allergen in Buckwheat Seeds: Fag t 6

Buckwheat is one of the five main allergenic foods (eggs, milk, wheat, buckwheat, and peanuts). Oleosin is an important type of allergen in some allergic foods. However, although most diagnostic nut and seed extracts are defatted, some patients with food allergies may have false negative diagnostic results of oleosin in vitro. Recently, we found that the serum of buckwheat allergic patients responded strongly to an 18 kDa protein. Mass spectrometry analysis showed it is the oleosin protein family. We further purified and evaluated the allergenicity of this buckwheat oleosin-type allergen, which is involved in the formation of buckwheat oil bodies. The tartary buckwheat oleosin allergen was named Fag t 6, according to the WHO/IUIS Allergen Nomenclature Subcommittee criteria. The DNA sequence of tartary buckwheat oleosin was cloned. Dot blot and enzyme-linked immunosorbent assay (ELISA) showed half of the 20 buckwheat allergic patients' serum had strong reactivity with purified buckwheat Fag t 6. Circular dichroism experiment analysis of its thermal stability showed a Tm of 64.65 ± 0.65 °C. A buckwheat allergy showed possible cross-reaction with a wheat allergy. In summary, this study not only increases our understanding of buckwheat allergies and oil-soluble allergens in general, it may also be used to improve diagnostic tests for buckwheat allergies in the future.

Biophysical characterization of full-length oleosin in dodecylphosphocholine micelles

Oleosin is a hydrophobic protein that punctuates the surface of plant seed lipid droplets, which are 20 nm-100 μm entities that serve as reservoirs for high-energy metabolites. Oleosin is purported to stabilize lipid droplets, but its exact mechanism of stabilization has not been established. Probing the structure of oleosin directly in lipid droplets is challenging due to the size of lipid droplets and their high degree of light scattering. Therefore, a medium in which the native structure of oleosin is retained, but is also amenable to spectroscopic studies is needed. Here, we show, using a suite of biophysical techniques, that dodecylphosphocholine micelles appear to support the tertiary structure of the oleosin protein (i.e., hairpin conformation) and render the protein in an oligomeric state that is amenable to more sophisticated biophysical techniques such as NMR.

Sesamum indicum Oleosin L improves oil packaging in Nicotiana benthamiana leaves

Plant oil production has been increasing continuously in the past decade. There has been significant investment in the production of high biomass plants with elevated oil content. We recently showed that the expression of Arabidopsis thaliana WRI1 and DGAT1 genes increase oil content by up to 15% in leaf dry weight tissue. However, triacylglycerols in leaf tissue are subject to degradation during senescence. In order to better package the oil, we expressed a series of lipid droplet proteins isolated from bacterial and plant sources in Nicotiana benthamiana leaf tissue. We observed further increases in leaf oil content of up to 2.3-fold when we co-expressed Sesamum indicum Oleosin L with AtWRI1 and AtDGAT1. Biochemical assays and lipid droplet visualization with confocal microscopy confirmed the increase in oil content and revealed a significant change in the size and abundance of lipid droplets.

Update on pollen-food allergy syndrome

INTRODUCTION

Allergies affect 20-30% of the population and respiratory allergies are mostly due to pollen grains from anemophilous plants. One to 5% of people suffer from food allergies and clinicians report increasing numbers of pollen-food allergy syndrome (PFAS), such that the symptoms have broadened from respiratory to gastrointestinal, and even to anaphylactic shock in the presence of cofactors. Thirty to 60% of food allergies are associated with pollen allergy while the percentage of pollen allergies associated to food allergy varies according to local environment and dietary habits.

AREAS COVERED

Articles published in peer-reviewed journals, covered by PubMed databank, clinical data are discussed including symptoms, diagnosis, and management. A chapter emphasizes the role of six well-known allergen families involved in PFAS: PR10 proteins, profilins, lipid transfer proteins, thaumatin-like proteins, isoflavone reductases, and β-1,3 glucanases. The relevance in PFAS of three supplementary allergen families is presented: oleosins, polygalacturonases, and gibberellin-regulated proteins. To support the discussion a few original relevant results were added.

EXPERT OPINION

Both allergenic sources, pollen and food, are submitted to the same stressful environmental changes resulting in an increase of pathogenesis-related proteins in which numerous allergens are found. This might be responsible for the potential increase of PFAS.

Ectopic Expression of OLEOSIN 1 and Inactivation of GBSS1 Have a Synergistic Effect on Oil Accumulation in Plant Leaves

During the transformation of wild-type (WT) Arabidopsis thaliana, a T-DNA containing OLEOSIN-GFP (OLE1-GFP) was inserted by happenstance within the GBSS1 gene, resulting in significant reduction in amylose and increase in leaf oil content in the transgenic line (OG). The synergistic effect on oil accumulation of combining gbss1 with the expression of OLE1-GFP was confirmed by transforming an independent gbss1 mutant (GABI_914G01) with OLE1-GFP. The resulting OLE1-GFP/gbss1 transgenic lines showed higher leaf oil content than the individual OLE1-GFP/WT or single gbss1 mutant lines. Further stacking of the lipogenic factors WRINKLED1, Diacylglycerol O-Acyltransferase (DGAT1), and Cys-OLEOSIN1 (an engineered sesame OLEOSIN1) in OG significantly elevated its oil content in mature leaves to 2.3% of dry weight, which is 15 times higher than that in WT Arabidopsis. Inducible expression of the same lipogenic factors was shown to be an effective strategy for triacylglycerol (TAG) accumulation without incurring growth, development, and yield penalties.

Lipid Body Dynamics in Shoot Meristems: Production, Enlargement, and Putative Organellar Interactions and Plasmodesmal Targeting

Post-embryonic cells contain minute lipid bodies (LBs) that are transient, mobile, engage in organellar interactions, and target plasmodesmata (PD). While LBs can deliver γ-clade 1,3-β-glucanases to PD, the nature of other cargo is elusive. To gain insight into the poorly understood role of LBs in meristems, we investigated their dynamics by microscopy, gene expression analyzes, and proteomics. In developing buds, meristems accumulated LBs, upregulated several LB-specific OLEOSIN genes and produced OLEOSINs. During bud maturation, the major gene OLE6 was strongly downregulated, OLEOSINs disappeared from bud extracts, whereas lipid biosynthesis genes were upregulated, and LBs were enlarged. Proteomic analyses of the LB fraction of dormant buds confirmed that OLEOSINs were no longer present. Instead, we identified the LB-associated proteins CALEOSIN (CLO1), Oil Body Lipase 1 (OBL1), Lipid Droplet Interacting Protein (LDIP), Lipid Droplet Associated Protein1a/b (LDAP1a/b) and LDAP3a/b, and crucial components of the OLEOSIN-deubiquitinating and degradation machinery, such as PUX10 and CDC48A. All mRFP-tagged LDAPs localized to LBs when transiently expressed in Nicotiana benthamiana. Together with gene expression analyzes, this suggests that during bud maturation, OLEOSINs were replaced by LDIP/LDAPs at enlarging LBs. The LB fraction contained the meristem-related actin7 (ACT7), "myosin XI tail-binding" RAB GTPase C2A, an LB/PD-associated γ-clade 1,3-β-glucanase, and various organelle- and/or PD-localized proteins. The results are congruent with a model in which LBs, motorized by myosin XI-k/1/2, traffic on F-actin, transiently interact with other organelles, and deliver a diverse cargo to PD.

Plant Lipid Bodies Traffic on Actin to Plasmodesmata Motorized by Myosin XIs

Late 19th-century cytologists observed tiny oil drops in shoot parenchyma and seeds, but it was discovered only in 1972 that they were bound by a half unit-membrane. Later, it was found that lipid bodies (LBs) arise from the endoplasmic reticulum. Seeds are known to be packed with static LBs, coated with the LB-specific protein OLEOSIN. As shown here, apices of Populustremula x P. tremuloides also express OLEOSIN genes and produce potentially mobile LBs. In developing buds, PtOLEOSIN (PtOLE) genes were upregulated, especially PtOLE6, concomitant with LB accumulation. To investigate LB mobility and destinations, we transformed Arabidopsis with PtOLE6-eGFP. We found that PtOLE6-eGFP fusion protein co-localized with Nile Red-stained LBs in all cell types. Moreover, PtOLE6-eGFP-tagged LBs targeted plasmodesmata, identified by the callose marker aniline blue. Pharmacological experiments with brefeldin, cytochalasin D, and oryzalin showed that LB-trafficking requires F-actin, implying involvement of myosin motors. In a triple myosin-XI knockout (xi-k/1/2), transformed with PtOLE6-eGFP, trafficking of PtOLE6-eGFP-tagged LBs was severely impaired, confirming that they move on F-actin, motorized by myosin XIs. The data reveal that LBs and OLEOSINs both function in proliferating apices and buds, and that directional trafficking of LBs to plasmodesmata requires the actomyosin system.

A space-saving visual screening method, Glycine max FAST, for generating transgenic soybean

Establishing homozygous transgenic lines of Glycine max is time-consuming and laborious. To overcome the difficulties, we developed a powerful method for selecting transgenic soybean plants, Fluorescence-Accumulating Seed Technology (GmFAST). GmFAST uses a marker composed of a soybean seed-specific promoter coupled to the OLE1-GFP gene, which encodes a GFP fusion of the oil-body membrane protein OLEOSIN1 of Arabidopsis thaliana. We introduced the marker gene into cotyledonary nodes of G. max Kariyutaka via Agrobacterium-mediated transformation and regenerated heterozygous transgenic plants. OLE1-GFP-expressing soybean seeds can be selected nondestructively with a fluorescence stereomicroscope. Among T2 seeds, the most strongly fluorescent seeds were homozygous. GmFAST enables to reduce the growing space by one-tenth compared with the conventional method. With this method, we obtained the soybean line that had higher levels of seed pods and oil production. The phenotypes are presumably caused by overexpression of Glyma13g30950, suggesting that Glyma13g30950 regulates seed pod formation in soybean plants. An increase in seed pod number was confirmed in A. thaliana plants that overexpressed the Arabidopsis ortholog of Glyma13g30950, E6L1.Taken together, GmFAST provides a space-saving visual and nondestructive screening method for soybean transformation, thereby increasing the chance of developing useful soybean lines.

Co-Compartmentation of Terpene Biosynthesis and Storage via Synthetic Droplet

Traditional bioproduct engineering focuses on pathway optimization, yet is often complicated by product inhibition, downstream consumption, and the toxicity of certain products. Here, we present the co-compartmentation of biosynthesis and storage via a synthetic droplet as an effective new strategy to improve the bioproduct yield, with squalene as a model compound. A hydrophobic protein was designed and introduced into the tobacco chloroplast to generate a synthetic droplet for terpene storage. Simultaneously, squalene biosynthesis enzymes were introduced to chloroplasts together with the droplet-forming protein to co-compartmentalize the biosynthesis and storage of squalene. The strategy has enabled a record yield of squalene at 2.6 mg/g fresh weight without compromising plant growth. Confocal fluorescent microscopy imaging, stimulated Raman scattering microscopy, and droplet composition analysis confirmed the formation of synthetic storage droplet in chloroplast. The co-compartmentation of synthetic storage droplet with a targeted metabolic pathway engineering represents a new strategy for enhancing bioproduct yield.

Genetic enhancement of oil content in potato tuber (Solanum tuberosum L.) through an integrated metabolic engineering strategy

Potato tuber is a high yielding food crop known for its high levels of starch accumulation but only negligible levels of triacylglycerol (TAG). In this study, we evaluated the potential for lipid production in potato tubers by simultaneously introducing three transgenes, including WRINKLED 1 (WRI1), DIACYLGLYCEROL ACYLTRANSFERASE 1 (DGAT1) and OLEOSIN under the transcriptional control of tuber-specific (patatin) and constitutive (CaMV-35S) promoters. This coordinated metabolic engineering approach resulted in over a 100-fold increase in TAG accumulation to levels up to 3.3% of tuber dry weight (DW). Phospholipids and galactolipids were also found to be significantly increased in the potato tuber. The increase of lipids in these transgenic tubers was accompanied by a significant reduction in starch content and an increase in soluble sugars. Microscopic examination revealed that starch granules in the transgenic tubers had more irregular shapes and surface indentations when compared with the relatively smooth surfaces of wild-type starch granules. Ultrastructural examination of lipid droplets showed their close proximity to endoplasmic reticulum and mitochondria, which may indicate a dynamic interaction with these organelles during the processes of lipid biosynthesis and turnover. Increases in lipid levels were also observed in the transgenic potato leaves, likely due to the constitutive expression of DGAT1 and incomplete tuber specificity of the patatin promoter. This study represents an important proof-of-concept demonstration of oil increase in tubers and provides a model system to further study carbon reallocation during development of nonphotosynthetic underground storage organs.

Comparative Lipidomics and Proteomics of Lipid Droplets in the Mesocarp and Seed Tissues of Chinese Tallow (Triadica sebifera)

Lipid droplets (LDs) are composed of a monolayer of phospholipids (PLs), surrounding a core of non-polar lipids that consist mostly of triacylglycerols (TAGs) and to a lesser extent diacylglycerols. In this study, lipidome analysis illustrated striking differences in non-polar lipids and PL species between LDs derived from Triadica sebifera seed kernels and mesocarp. In mesocarp LDs, the most abundant species of TAG contained one C18:1 and two C16:0 and fatty acids, while TAGs containing three C18 fatty acids with higher level of unsaturation were dominant in the seed kernel LDs. This reflects the distinct differences in fatty acid composition of mesocarp (palmitate-rich) and seed-derived oil (α-linoleneate-rich) in T. sebifera. Major PLs in seed LDs were found to be rich in polyunsaturated fatty acids, in contrast to those with relatively shorter carbon chain and lower level of unsaturation in mesocarp LDs. The LD proteome analysis in T. sebifera identified 207 proteins from mesocarp, and 54 proteins from seed kernel, which belong to various functional classes including lipid metabolism, transcription and translation, trafficking and transport, cytoskeleton, chaperones, and signal transduction. Oleosin and lipid droplets associated proteins (LDAP) were found to be the predominant proteins associated with LDs in seed and mesocarp tissues, respectively. We also show that LDs appear to be in close proximity to a number of organelles including the endoplasmic reticulum, mitochondria, peroxisomes, and Golgi apparatus. This comparative study between seed and mesocarp LDs may shed some light on the structure of plant LDs and improve our understanding of their functionality and cellular metabolic networks in oleaginous plant tissues.

Tapetal oleosins play an essential role in tapetosome formation and protein relocation to the pollen coat

The Arabidopsis pollen grain is covered by a lipidic pollen coat representing select constituents released upon the programmed cell death of the anther secretory tapetum. These constituents originate primarily from two specialized tapetal organelles, elaioplasts and tapetosomes. Tapetosomes are distinctive Brassicaceae organelles derived from the endoplasmic reticulum that store triacylglycerols, flavonoids, alkanes, and proteins. The tapetosome triacylglycerols are found within lipid droplets surrounded by the highly variable tapetal oleosins that eventually generate the most abundant proteins of the pollen coat. Many questions remain regarding the sub-cellular targeting of tapetal oleosins as well as their role in tapetosome formation. Translational fusions of different tapetal oleosins or their derived domains to marker proteins were introduced into Arabidopsis thaliana to investigate their localization, processing and function. Arabidopsis tapetal oleosins were shown to be proteolytically cleaved following tapetum degeneration and different protein domains were targeted to the pollen coat despite vast differences in composition and size. Importantly, specific fusions were discovered to affect distinct aspects of tapetosome formation. This report not only highlighted the critical role of individual tapetal oleosin domains in Arabidopsis tapetosome formation, but revealed translational fusions to be a valuable tool in deciphering this evidently complex developmental process.

Superparamagnetic iron oxide nanoparticle micelles stabilized by recombinant oleosin for targeted magnetic resonance imaging

Recombinant surfactants present a new platform for stabilizing and targeting nanoparticle imaging agents. Superparamagnetic iron oxide nanoparticle-loaded micelles for MRI contrast are stabilized by an engineered variant of the naturally occurring protein oleosin and targeted using a Her2/neu affibody-oleosin fusion. The recombinant oleosin platform allows simple targeting and the ability to easily swap the ligand for numerous targets.

Proteomic analysis of oil body membrane proteins accompanying the onset of desiccation phase during sunflower seed development

A noteworthy metabolic signature accompanying oil body (OB) biogenesis during oilseed development is associated with the modulation of the oil body membranes proteins. Present work focuses on 2-dimensional polyacrylamide gel electrophoresis (2-D PAGE)-based analysis of the temporal changes in the OB membrane proteins analyzed by LC-MS/MS accompanying the onset of desiccation (20-30 d after anthesis; DAA) in the developing seeds of sunflower (Helianthus annuus L.). Protein spots unique to 20-30 DAA stages were picked up from 2-D gels for identification and the identified proteins were categorized into 7 functional classes. These include proteins involved in energy metabolism, reactive oxygen scavenging, proteolysis and protein turnover, signaling, oleosin and oil body biogenesis-associated proteins, desiccation and cytoskeleton. At 30 DAA stage, exclusive expressions of enzymes belonging to energy metabolism, desiccation and cytoskeleton were evident which indicated an increase in the metabolic and enzymatic activity in the cells at this stage of seed development (seed filling). Increased expression of cruciferina-like protein and dehydrin at 30 DAA stage marks the onset of desiccation. The data has been analyzed and discussed to highlight desiccation stage-associated metabolic events during oilseed development.

Metabolic engineering of biomass for high energy density: oilseed-like triacylglycerol yields from plant leaves

High biomass crops have recently attracted significant attention as an alternative platform for the renewable production of high energy storage lipids such as triacylglycerol (TAG). While TAG typically accumulates in seeds as storage compounds fuelling subsequent germination, levels in vegetative tissues are generally low. Here, we report the accumulation of more than 15% TAG (17.7% total lipids) by dry weight in Nicotiana tabacum (tobacco) leaves by the co-expression of three genes involved in different aspects of TAG production without severely impacting plant development. These yields far exceed the levels found in wild-type leaf tissue as well as previously reported engineered TAG yields in vegetative tissues of Arabidopsis thaliana and N. tabacum. When translated to a high biomass crop, the current levels would translate to an oil yield per hectare that exceeds those of most cultivated oilseed crops. Confocal fluorescence microscopy and mass spectrometry imaging confirmed the accumulation of TAG within leaf mesophyll cells. In addition, we explored the applicability of several existing oil-processing methods using fresh leaf tissue. Our results demonstrate the technical feasibility of a vegetative plant oil production platform and provide for a step change in the bioenergy landscape, opening new prospects for sustainable food, high energy forage, biofuel and biomaterial applications.

Refurbishing the plasmodesmal chamber: a role for lipid bodies?

Lipid bodies (LBs) are universal constituents of both animal and plant cells. They are produced by specialized membrane domains at the tubular endoplasmic reticulum (ER), and consist of a core of neutral lipids and a surrounding monolayer of phospholipid with embedded amphipathic proteins. Although originally regarded as simple depots for lipids, they have recently emerged as organelles that interact with other cellular constituents, exchanging lipids, proteins and signaling molecules, and shuttling them between various intracellular destinations, including the plasmamembrane (PM). Recent data showed that in plants LBs can deliver a subset of 1,3-β-glucanases to the plasmodesmal (PD) channel. We hypothesize that this may represent a more general mechanism, which complements the delivery of glycosylphosphatidylinositol (GPI)-anchored proteins to the PD exterior via the secretory pathway. We propose that LBs may contribute to the maintenance of the PD chamber and the delivery of regulatory molecules as well as proteins destined for transport to adjacent cells. In addition, we speculate that LBs deliver their cargo through interaction with membrane domains in the cytofacial side of the PM.

A non-destructive screenable marker, OsFAST, for identifying transgenic rice seeds

The production of transgenic plants has contributed greatly to plant research. Previously, an improved method for screening transgenic Arabidopsis thaliana seeds using the FAST (Fluorescence-Accumulating-Seed Technology) method and FAST marker was reported. Arabidopsis seeds containing the FAST marker may be visually screened using a fluorescence stereomicroscope or blue LED handy-type instrument. Although the FAST method was originally designed for Arabidopsis screens, this study endeavors to adapt this method for the screening of other plants. Here, an optimized technology, designated the OsFAST method, is presented as a useful tool for screening transgenic rice seeds. The OsFAST method is based on the expression of the OsFAST-G marker under the control of a seed-embryo-specific promoter, similar to the Arabidopsis FAST-G marker. The OsFAST method provides a simple and non-destructive method for identifying transgenic rice seeds. It is proposed that the FAST method is adaptable to various plant species and will enable a deeper analysis of the floral-dip method. 

Functional diversity of the plant glycine-rich proteins superfamily

The first plant glycine-rich proteins (GRPs) have been isolated more than 20 years ago based on their specific expression pattern and/or modulation by several biotic and abiotic factors. This superfamily is characterized by the presence of a glycine-rich domain arranged in (Gly)(n)-X repeats. The presence of additional motifs, as well as the nature of the glycine repeats, groups them in different classes. The diversity in structure as well as in expression pattern, modulation and sub-cellular localization have always indicated that these proteins, although classified as members of the same superfamily, would perform different functions in planta. Only now, two decades later, with the first functional characterizations of plant GRPs their involvement in diverse biological and biochemical processes are being uncovered. Here, we review the so far ascribed functions of plant GRPs.

Activation of a pollenin promoter upon nematode infection

Three glycine-rich protein genes of Arabidopsis thaliana (Atgrp-6, Atgrp-7, and Atgrp-8) that correspond to putative genes coding for pollenins (AtolnB;2, AtolnB;3, and AtolnB;4, respectively) are expressed predominantly in the anthers and, more specifically, in the tapetum layer. Tapetal cells are responsible for nutrition of developing pollen grains and show some functional similarities to nematode feeding sites (NFS) induced in plant roots by sedentary parasitic nematodes. The aim of this study was to analyze promoter activity of the Atgrp genes in NFS. Transformed Arabidopsis plants containing a promoter-ss-glucuronidase (gus) fusion of the Atgrp-7 gene were inoculated with the root-knot nematode Meloidogyne incognita and the cyst nematode Heterodera schachtii. GUS assays were performed at different time points after infection. Histochemical analysis revealed an up-regulation of Atgrp-7-gus expression 3 days after inoculation in the feeding sites of both nematodes. Maximal Atgrp-7-gus staining levels in NFS were observed 1 week after nematode infection.