Unsaturated Lipids Change in Olive Tree Drupe and Seed during Fruit Development and in Response to Cold-Stress and Acclimation

Development of a rapid and fruit-saving method for fatty acid composition analysis in olive: a comparative study on 27 cultivars

Fatty acid composition is an essential aspect of the qualitative assessment of olive oil. A method for evaluating and trending fatty acid composition of olive varieties directly from a limited amount of drupes, has been proven reliable in comparison with traditional oil analysis. No significant difference was detected between the two methods for the 27 cultivars tested, despite presenting decidedly different acid compositions. The results obtained, crossed with those of oil yield, can represent a useful resource to set the harvest calendars by choosing the most suitable time for the production of superior quality oils and for reducing the risk of pathogen infections or pest attack. For three cultivars, the acid composition was evaluated during three ripening phases (green, veraisoned and veraisoned to black). The different behaviors suggest it is the genotype that determines this -still little known- physiological trait in olive. An interesting finding was that the oils from drupes harvested in August showed linolenic acid values higher than the limit (1.00%) set in the international standards for the classification of olive oils, requesting further investigation.

Expression of FAD and SAD Genes in Developing Seeds of Flax Varieties under Different Growth Conditions

Flax seed is one of the richest plant sources of linolenic acid (LIN) and also contains unsaturated linoleic acid (LIO) and oleic acid (OLE). Stearoyl-ACP desaturases (SADs) and fatty acid desaturases (FADs) play key roles in the synthesis of flax fatty acids (FAs). However, there is no holistic view of which genes from the SAD and FAD families and at which developmental stages have the highest expression levels in flax seeds, as well as the influence of genotype and growth conditions on the expression profiles of these genes. We sequenced flax seed transcriptomes at 3, 7, 14, 21, and 28 days after flowering (DAF) for ten flax varieties with different oil FA compositions grown under three temperature/watering conditions. The expression levels of 25 genes of the SAD, FAD2, and FAD3 families were evaluated. FAD3b, FAD3a, FAD2b-2, SAD3-1, SAD2-1, SAD2-2, SAD3-2, FAD2a-1, and FAD2a-2 had the highest expression levels, which changed significantly during seed development. These genes probably play a key role in FA synthesis in flax seeds. High temperature and insufficient watering shifted the maximum expression levels of FAD and SAD genes to earlier developmental stages, while the opposite trend was observed for low temperature and excessive watering. Differences in the FAD and SAD expression profiles under different growth conditions may affect the FA composition of linseed oil. Stop codons in the FAD3a gene, resulting in a reduced LIN content, decreased the level of FAD3a transcript. The obtained results provide new insights into the synthesis of linseed oil.

Genome-Wide Characterization and Expression Analysis of Fatty acid Desaturase Gene Family in Poplar

Fatty acid desaturases (FADs) modulate carbon–carbon single bonds to form carbon–carbon double bonds in acyl chains, leading to unsaturated fatty acids (UFAs) that have vital roles in plant growth and development and their response to environmental stresses. In this study, a total of 23 Populus trichocarpaFAD (PtFAD) candidates were identified from the poplar genome and clustered into seven clades, including FAB2, FAD2, FAD3/7/8, FAD5, FAD6, DSD, and SLD. The exon–intron compositions and conserved motifs of the PtFADs, clustered into the same clade, were considerably conserved. It was found that segmental duplication events are predominantly attributable to the PtFAD gene family expansion. Several hormone- and stress-responsive elements in the PtFAD promoters implied that the expression of the PtFAD members was complicatedly regulated. A gene expression pattern analysis revealed that some PtFAD mRNA levels were significantly induced by abiotic stress. An interaction proteins and gene ontology (GO) analysis indicated that the PtFADs are closely associated with the UFAs biosynthesis. In addition, the UFA contents in poplars were significantly changed under drought and salt stresses, especially the ratio of linoleic and linolenic acids. The integration of the PtFAD expression patterns and UFA contents showed that the abiotic stress-induced PtFAD3/7/8 members mediating the conversion of linoleic and linolenic acids play vital roles in response to osmotic stress. This study highlights the profiles and functions of the PtFADs and identifies some valuable genes for forest improvements.

Identifying volatile and non-volatile organic compounds to discriminate cultivar, growth location, and stage of ripening in olive fruits and oils

BACKGROUND

There is increasing consumer demand for olive oil to be traceable. However, genotype, environmental factors, and stage of maturity, all affect the flavor and composition of both the olives and olive oil. Few studies have included all three variables. Key metabolites include lipids, phenolics, and a wide range of volatile organic compounds (VOCs), which provide the olives and oil with their characteristic flavor. Here we aim to identify markers that are able to discriminate between cultivars, that can identify growth location, and can discriminate stages of fruit maturity. 'Nocellara messinese' and 'Carolea' olive fruits were grown at three locations differing in altitude in Calabria, Italy, and harvested at three stages of maturity. Oil was analyzed from the two most mature stages.

RESULTS

Nine and 20 characters discriminated all fruit and oil samples respectively, and relative abundance of two fatty acids distinguished all oils. Whole VOC profiles discriminated among the least mature olives, and oil VOC profiles discriminated location and cultivar at both stages. Three VOCs putatively identified as hexanal, methyl acetate, and 3-hexen-1-ol differentiated all samples of oils from the most mature fruit stage.

CONCLUSION

The results confirm that interactions of location, cultivar and fruit maturity stage are critical for the overall pattern of aroma compounds, and identify potential markers of commercial relevance. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact of Cold Stress on Leaf Structure, Photosynthesis, and Metabolites in Camellia weiningensis and C. oleifera Seedlings

Camellia weiningensis Y. K. Li. sp. nov. (CW) is an endemic oil-tea species in Guizhou province, distributed in the alpine karst area, which exhibits cold resistance and better economic characters than C. oleifera (CO). The mechanism of cold response in CW seedlings has not been studied in depth. Herein, we performed anatomical, physiological, and metabolic analyses to assess the impact of cold stress on leaf structure, photosynthesis, and metabolites in CW and CO seedlings. Anatomical analysis of leaves showed CW seedlings had greater leaf and palisade thicknesses, tissue structure tightness, and palisade-spongy tissue ratio to enhance chilling stress (4 °C) tolerance, but freezing stress (−4 °C) caused loosening of the leaf tissue structure in both CW and CO seedlings. Photosynthetic analysis showed a reduction in the chlorophyll (Chl) fluorescence (Fv/Fm) and photosynthetic parameters under freezing stress in both CW and CO seedlings. Cold stress increased the abscisic acid (ABA) contents in both the Camellia species, and CW exhibited the highest ABA content under −4 °C treatment. Additionally, the indole-3-acetic acid (IAA) content was also increased in CW in response to cold stress. An obviously distinct metabolite composition was observed for CW and CO under different temperatures, and significantly changed metabolites (SCMs) were enriched under freezing stress. Prenol lipids, organooxygen compounds, and fatty acyls were the main metabolites in the two Camellia species in response to cold stress. The top key SCMs, such as medicoside G, cynarasaponin F, yuccoside C, and methionyl-proline were downregulated under freezing stress in both CW and CO. The contents of some key metabolites associated with sugar metabolism, such as UDP-glucose, UDP-D-apiose, and fructose 6-phosphate, were higher in CW than in CO, which may contribute to enhancing the cold resistance in CW. Our findings are helpful in explaining how CW adapt to alpine karst cold environments, and will provide a reference for cold tolerance improvement and application of stress-resistant breeding of Camellia in alpine and cold areas.

Comparative Analysis and Structural Modeling of Elaeis oleifera FAD2, a Fatty Acid Desaturase Involved in Unsaturated Fatty Acid Composition of American Oil Palm

American oil palm (Elaeis oleifera) is an important source of dietary oil that could fulfill the increasing worldwide demand for cooking oil. Therefore, improving its production is crucial and could be realized through breeding and genetic engineering approaches aiming to obtain high-yielding varieties with improved oil content and quality. The fatty acid composition and particularly the oleic/linoleic acid ratio are major factors influencing oil quality. Our work focused on a fatty acid desaturase (FAD) enzyme involved in the desaturation and conversion of oleic acid to linoleic acid. Following the in silico identification and annotation of Elaeis oleifera FAD2, its molecular and structural features characterization was performed to better understand the mechanistic bases of its enzymatic activity. EoFAD2 is 1173 nucleotides long and encodes a protein of 390 amino acids that shares similarities with other FADs. Interestingly, the phylogenetic study showed three distinguished groups where EoFAD2 clustered among monocotyledonous taxa. EoFAD2 is a membrane-bound protein with five transmembrane domains presumably located in the endoplasmic reticulum. The homodimer organization model of EoFAD2 enzyme and substrates and respective substrate-binding residues were predicted and described. Moreover, the comparison between 24 FAD2 sequences from different species generated two interesting single-nucleotide polymorphisms (SNPs) associated with the oleic/linoleic acid contents.

The Combination of Abscisic Acid (ABA) and Water Stress Regulates the Epicuticular Wax Metabolism and Cuticle Properties of Detached Citrus Fruit

The phytohormone abscisic acid (ABA) is a major regulator of fruit response to water stress, and may influence cuticle properties and wax layer composition during fruit ripening. This study investigates the effects of ABA on epicuticular wax metabolism regulation in a citrus fruit cultivar with low ABA levels, called Pinalate (Citrus sinensis L. Osbeck), and how this relationship is influenced by water stress after detachment. Harvested ABA-treated fruit were exposed to water stress by storing them at low (30-35%) relative humidity. The total epicuticular wax load rose after fruit detachment, which ABA application decreased earlier and more markedly during fruit-dehydrating storage. ABA treatment changed the abundance of the separated wax fractions and the contents of most individual components, which reveals dependence on the exposure to postharvest water stress and different trends depending on storage duration. A correlation analysis supported these responses, which mostly fitted the expression patterns of the key genes involved in wax biosynthesis and transport. A cluster analysis indicated that storage duration is an important factor for the exogenous ABA influence and the postharvest environment on epicuticular wax composition, cuticle properties and fruit physiology. Dynamic ABA-mediated reconfiguration of wax metabolism is influenced by fruit exposure to water stress conditions.

Influence of substrate inclusion of quail manure on the growth performance, body composition, fatty acid and amino acid profiles of black soldier fly larvae (Hermetia illucens)

In recent years, monounsaturated fatty acids (MUFAs), especially palmitoleic acid (omega-7, POA) and oleic acid (omega-9, OA), have gained increasing notoriety; however, traditional sources of MUFAs have not achieved sustainability. Black soldier fly (BSF) larvae can convert low-quality products into high-quality biomass to be used in many industrial applications. Therefore, this study aims to assess increasing of quail manure on the biological traits of BSF larvae and the bioaccumulation of MUFAs by BSF larvae reared on quail manure, which causes many harmful effects to the environment. Different concentrations of quail manure from 0 to 100% were mixed with wheat bran. The inclusion of quail manure in the substrate resulted in (1) a decrease in saturated fatty acids by 20.20%, (2) accumulation of OA (47.36%), (3) biosynthesis of POA (157.73%) in BSF larvae, and (4) no significant differences in total protein (~38%) or essential amino acids (~43%) of BSF larvae. Inclusion of 40% of quail manure improved the performance of BSF larvae. Therefore, rearing BSF larvae on quail manure is considered to be a renewable and sustainable source of omega-7 and omega-9 for nutraceutical production, pharmaceutical uses, or animal food additives to achieve circular food production.

Dynamic transcriptome analysis identifies genes related to fatty acid biosynthesis in the seeds of Prunus pedunculata Pall

BACKGROUND

Prunus pedunculata Pall, the deciduous shrub of Amygdalus subgenus in Rosaceae, is a new kind of desert oil-bearing tree. It has a long story of being planted in the West and North of China for sand fixation and desert control. In addition, the seeds of P. pedunculata are rich of oil, especially the monounsaturated fatty acid and polyunsaturated fatty acid. However, little is known about the molecular mechanisms of oil accumulation during the seed development of P. pedunculata.

RESULTS

The seeds of P. pedunculata from three independent plants at 10, 18, 24, 31, 39, 45, 59 and 73 days after flowering (DAF) were obtained and the oil compositions were evaluated. It showed that oleic acid was the dominant type of oil content in the mature seeds (from 32.724% at 10DAF to 72.06% at 73DAF). Next, transcriptome sequencing for the developing seeds produced 988.795 million high quality reads and TRINITY assembled 326,271 genes for the first transcriptome for P. pedunculata. After the assembled transcriptome was evaluated by BUSCO with 85.9% completeness, we identified 195,342, 109,850 and 121,897 P. pedunculata genes aligned to NR, GO and KEGG pathway databases, respectively. Then, we predicted 23,229 likely proteins from the assembled transcriptome and identified 1917 signal peptides and 5512 transmembrane related proteins. In the developing seeds we detected 91,362 genes (average FPKM > 5) and correlation analysis indicated three possible development stages - early (10 ~ 24DAF), middle (31 ~ 45DAF) and late (59 ~ 73DAF). We next analyzed the differentially expressed genes (DEGs) in the developing seeds. Interestingly, compared to 10DAF the number of DEGs was increased from 4406 in 18DAF to 27,623 in 73DAF. Based on the gene annotation, we identified 753, 33, 8 and 645 DEGs related to the fatty acid biosynthesis, lipid biosynthesis, oil body and transcription factors. Notably, GPAT, DGD1, LACS2, UBC and RINO were highly expressed at the early development stage, ω6-FAD, SAD, ACP, ACCA and AHG1 were highly expressed at the middle development stage, and LACS6, DGD1, ACAT1, AGPAT, WSD1, EGY2 and oleosin genes were highly expressed at the late development stage.

CONCLUSIONS

This is the first time to study the developing seed transcriptome of P. pedunculata and our findings will provide a valuable resource for future studies. More importantly, it will improve our understanding of molecular mechanisms of oil accumulation in P. pedunculata.

Identification of differentially expressed genes involved in amino acid and lipid accumulation of winter turnip rape (Brassica rapa L.) in response to cold stress

Winter turnip rape (Brassica rapa L.) is an important overwintering oil crop that is widely planted in northwestern China. It considered to be a good genetic resource for cold-tolerant research because its roots can survive harsh winter conditions. Here, we performed comparative transcriptomics analysis of the roots of two winter turnip rape varieties, Longyou7 (L7, strong cold tolerance) and Tianyou2 (T2, low cold tolerance), under normal condition (CK) and cold stress (CT) condition. A total of 8,366 differentially expressed genes (DEGs) were detected between the two L7 root groups (L7CK_VS_L7CT), and 8,106 DEGs were detected for T2CK_VS_T2CT. Among the DEGs, two ω-3 fatty acid desaturase (FAD3), two delta-9 acyl-lipid desaturase 2 (ADS2), one diacylglycerol kinase (DGK), and one 3-ketoacyl-CoA synthase 2 (KCS2) were differentially expressed in the two varieties and identified to be related to fatty acid synthesis. Four glutamine synthetase cytosolic isozymes (GLN), serine acetyltransferase 1 (SAT1), and serine acetyltransferase 3 (SAT3) were down-regulated under cold stress, while S-adenosylmethionine decarboxylase proenzyme 1 (AMD1) had an up-regulation tendency in response to cold stress in the two samples. Moreover, the delta-1-pyrroline-5-carboxylate synthase (P5CS), δ-ornithine aminotransferase (δ-OAT), alanine-glyoxylate transaminase (AGXT), branched-chain-amino-acid transaminase (ilvE), alpha-aminoadipic semialdehyde synthase (AASS), Tyrosine aminotransferase (TAT) and arginine decarboxylase related to amino acid metabolism were identified in two cultivars variously expressed under cold stress. The above DEGs related to amino acid metabolism were suspected to the reason for amino acids content change. The RNA-seq data were validated by real-time quantitative RT-PCR of 19 randomly selected genes. The findings of our study provide the gene expression profile between two varieties of winter turnip rape, which lay the foundation for a deeper understanding of the highly complex regulatory mechanisms in plants during cold treatment.

The fluid-mosaic membrane theory in the context of photosynthetic membranes: Is the thylakoid membrane more like a mixed crystal or like a fluid?

Since the publication of the fluid-mosaic membrane theory by Singer and Nicolson in 1972 generations of scientists have adopted this fascinating concept for all biological membranes. Assuming the membrane as a fluid implies that the components embedded in the lipid bilayer can freely diffuse like swimmers in a water body. During the detailed biochemical analysis of the thylakoid protein components of chloroplasts from higher plants and algae, in the '80 s and '90 s it became clear that photosynthetic membranes are not homogeneous either in the vertical or the lateral directions. The lateral heterogeneity became obvious by the differentiation of grana and stroma thylakoids, but also the margins have been identified with a highly specific protein pattern. Further refinement of the fluid mosaic model was needed to take into account the presence of non-bilayer lipids, which are the most abundant lipids in all energy-converting membranes, and the polymorphism of lipid phases, which has also been documented in thylakoid membranes. These observations lead to the question, how mobile the components are in the lipid phase and how this ordering is made and maintained and how these features might be correlated with the non-bilayer propensity of the membrane lipids. Assuming instead of free diffusion, a "controlled neighborhood" replaced the model of fluidity by the model of a "mixed crystal structure". In this review we describe why basic photosynthetic regulation mechanisms depend on arrays of crystal-like lipid-protein macro-assemblies. The mechanisms which define the ordering in macrodomains are still not completely clear, but some recent experiments give an idea how this fascinating order is produced, adopted and maintained. We use the operation of the xanthophyll cycle as a rather well understood model challenging and complementing the standard Singer-Nicolson model via assigning special roles to non-bilayer lipids and non-lamellar lipid phases in the structure and function of thylakoid membranes.

Characterization and validation of olive FAD and SAD gene families: expression analysis in different tissues and during fruit development

Stearoyl-ACP desaturases (SADs) and fatty acid desaturases (FADs) play a critical role in plant lipid metabolism and also affect oil fatty acid composition introducing double bonds into the hydrocarbon chains to produce unsaturated fatty acids. In the present study, the genomic sequences of three SAD and three FAD candidate genes were characterized in olive and their expression was evaluated in different plant tissues. OeSAD genes corresponded to olive SAD1 and SAD2 and to a newly identified OeSAD4, sharing the conserved protein structure with other plant species. On the other hand, the full-length genomic sequences of two microsomal OeFAD genes (FAD2-1 and FAD2-2) and the plastidial FAD6, were released. When the level of expression was tested on different tissues of cv. Leccino, OeSAD1 and OeSAD2 were mainly expressed in the fruits, while OeFAD genes showed the lowest expression in this tissue. The mRNA profiling of all genes was directly studied in fruits of Leccino and Coratina cultivars during fruit development. In both genotypes, the expression level of OeSAD1 and OeSAD2 had the highest value during and after the pit-hardening period, when oil accumulation in fruit mesocarp is intensively increasing. Furthermore, the expression level of both OeFAD2 genes, which were the main candidates for oleic acid desaturation, were almost negligible during fruit ripening. These results have made possible to define candidate genes of the machinery regulation of fatty acid composition in olive oil, providing information on their sequence, gene structure and chromosomal location.

Characterization of cold stress responses in different rapeseed ecotypes based on metabolomics and transcriptomics analyses

The winter oilseed ecotype is more tolerant to low temperature than the spring ecotype. Transcriptome and metabolome analyses of leaf samples of five spring Brassica napus L. (B. napus) ecotype lines and five winter B. napus ecotype lines treated at 4 °C and 28 °C were performed. A total of 25,460 differentially expressed genes (DEGs) of the spring oilseed ecotype and 28,512 DEGs of the winter oilseed ecotype were identified after cold stress; there were 41 differentially expressed metabolites (DEMs) in the spring and 47 in the winter oilseed ecotypes. Moreover, more than 46.2% DEGs were commonly detected in both ecotypes, and the extent of the changes were much more pronounced in the winter than spring ecotype. By contrast, only six DEMs were detected in both the spring and winter oilseed ecotypes. Eighty-one DEMs mainly belonged to primary metabolites, including amino acids, organic acids and sugars. The large number of specific genes and metabolites emphasizes the complex regulatory mechanisms involved in the cold stress response in oilseed rape. Furthermore, these data suggest that lipid, ABA, secondary metabolism, signal transduction and transcription factors may play distinct roles in the spring and winter ecotypes in response to cold stress. Differences in gene expression and metabolite levels after cold stress treatment may have contributed to the cold tolerance of the different oilseed ecotypes.

Changes in gene expression and metabolic profile of drupes of Olea europaea L. cv Carolea in relation to maturation stage and cultivation area

BACKGROUND

Olive (Olea europaea L.) is an emblematic oil tree crop in the Mediterranean basin. Currently, despite olive features as a moderately thermophilic species, its cultivation is worldwide spreading due to the health-related impact of olive products on human nutrition. A point of concern for the expanding olive cultivation is related to the influence that, in addition to genotype, environmental factors exerts on drupe development and metabolism with consequent impact on fruit key traits. In this context, the aim of the present work was to gain further information on the genetic networks controlling drupe maturation phase and, mainly, on their modulation in response to environmental cues.

RESULTS

To achieve this goal, a comparative transcriptome-wide investigation was carried out on drupes of Olea europaea cultivar Carolea, collected from plants growing in areas at different altitude level and therefore experiencing different climatic conditions. Two maturation stages of drupe were analysed: green mature and turning-purple. Metabolic characterization of drupe was also performed. At both transcriptomic and metabolic level differences were detected in the pathway of fatty acids (FAs) and phenol compounds, in relation to both drupe maturation stage and cultivation area. Among the most relevant differences detected during the transition from GM to TP stages there were: the upregulation of FADs genes in the drupes of population growing at 700 masl, the upregulation of phenol biosynthesis-related genes in drupes growing at 10 and 200 masl and very interestingly the downregulation of specific genes involved in secoiridoids production in drupes growing at 700 masl. Globally, these results suggested that stability of FAs and phenols, mainly of secoiridoids group, is promoted at high altitude, while at lower altitude phenol biosynthesis is prolonged.

CONCLUSION

The obtained results showed a differential modulation of genetic pathways related to olive compound quality in relation to the cultivation area, likely imposed by the different temperature impending at each altitude. The derived molecular information appears of interest for both breeding and biotechnological programs of olive species, especially with respect to the modulation of antioxidant secoiridoid compounds which play a key role in conferring both sensorial and healthy characteristic to olive products.

Chloroplasts- Beyond Energy Capture and Carbon Fixation: Tuning of Photosynthesis in Response to Chilling Stress

As organelles for photosynthesis in green plants, chloroplasts play a vital role in solar energy capture and carbon fixation. The maintenance of normal chloroplast physiological functions is essential for plant growth and development. Low temperature is an adverse environmental stress that affects crop productivity. Low temperature severely affects the growth and development of plants, especially photosynthesis. To date, many studies have reported that chloroplasts are not only just organelles of photosynthesis. Chloroplasts can also perceive chilling stress signals via membranes and photoreceptors, and they maintain their homeostasis and promote photosynthesis by regulating the state of lipid membranes, the abundance of photosynthesis-related proteins, the activity of enzymes, the redox state, and the balance of hormones and by releasing retrograde signals, thus improving plant resistance to low temperatures. This review focused on the potential functions of chloroplasts in fine tuning photosynthesis processes under low-temperature stress by perceiving stress signals, modulating the expression of photosynthesis-related genes, and scavenging excess reactive oxygen species (ROS) in chloroplasts to survive the adverse environment.

Sphingolipid Distribution, Content and Gene Expression during Olive-Fruit Development and Ripening

Plant sphingolipids are involved in the building of the matrix of cell membranes and in signaling pathways of physiological processes and environmental responses. However, information regarding their role in fruit development and ripening, a plant-specific process, is unknown. The present study seeks to determine whether and, if so, how sphingolipids are involved in fleshy-fruit development and ripening in an oil-crop species such as olive (Olea europaea L. cv. Picual). Here, in the plasma-membranes of live protoplasts, we used fluorescence to examine various specific lipophilic stains in sphingolipid-enriched regions and investigated the composition of the sphingolipid long-chain bases (LCBs) as well as the expression patterns of sphingolipid-related genes, OeSPT, OeSPHK, OeACER, and OeGlcCerase, during olive-fruit development and ripening. The results demonstrate increased sphingolipid content and vesicle trafficking in olive-fruit protoplasts at the onset of ripening. Moreover, the concentration of LCB [t18:1(8Z), t18:1 (8E), t18:0, d18:2 (4E/8Z), d18:2 (4E/8E), d18:1(4E), and 1,4-anhydro-t18:1(8E)] increases during fruit development to reach a maximum at the onset of ripening, although these molecular species decreased during fruit ripening. On the other hand, OeSPT, OeSPHK, and OeGlcCerase were expressed differentially during fruit development and ripening, whereas OeACER gene expression was detected only at the fully ripe stage. The results provide novel data about sphingolipid distribution, content, and biosynthesis/turnover gene transcripts during fleshy-fruit ripening, indicating that all are highly regulated in a developmental manner.

Effects of Chilling on the Structure, Function and Development of Chloroplasts

Chloroplasts are the organelles that perform energy transformation in plants. The normal physiological functions of chloroplasts are essential for plant growth and development. Chilling is a common environmental stress in nature that can directly affect the physiological functions of chloroplasts. First, chilling can change the lipid membrane state and enzyme activities in chloroplasts. Then, the efficiency of photosynthesis declines, and excess reactive oxygen species (ROS) are produced. On one hand, excess ROS can damage the chloroplast lipid membrane; on the other hand, ROS also represent a stress signal that can alter gene expression in both the chloroplast and nucleus to help regenerate damaged proteins, regulate lipid homeostasis, and promote plant adaptation to low temperatures. Furthermore, plants assume abnormal morphology, including chlorosis and growth retardation, with some even exhibiting severe necrosis under chilling stress. Here, we review the response of chloroplasts to low temperatures and focus on photosynthesis, redox regulation, lipid homeostasis, and chloroplast development to elucidate the processes involved in plant responses and adaptation to chilling stress.

Bioactive lipids in gintonin-enriched fraction from ginseng

Background

Ginseng is a traditional herbal medicine for human health. Ginseng contains a bioactive ligand named gintonin. The active ingredient of gintonin is lysophosphatidic acid C18:2 (LPA C18:2). We previously developed a method for gintonin-enriched fraction (GEF) preparation to mass-produce gintonin from ginseng. However, previous studies did not show the presence of other bioactive lipids besides LPAs. The aim of this study was to quantify the fatty acids, lysophospholipids (LPLs), and phospholipids (PLs) besides LPAs in GEF.

Methods

We prepared GEF from white ginseng. We used gas chromatography-mass spectrometry for fatty acid analysis and liquid chromatography-tandem mass spectrometry for PL analysis, and quantified the fatty acids, LPLs, and PLs in GEF using respective standards. We examined the effect of GEF on insulin secretion in INS-1 cells.

Results

GEF contains about 7.5% linoleic (C18:2), 2.8% palmitic (C16:0), and 1.5% oleic acids (C18:1). GEF contains about 0.2% LPA C18:2, 0.06% LPA C16:0, and 0.02% LPA C18:1. GEF contains 0.08% lysophosphatidylcholine, 0.03% lysophosphatidylethanolamine, and 0.13% lysophosphatidylinositols. GEF also contains about 1% phosphatidic acid (PA) 16:0-18:2, 0.5% PA 18:2-18:2, and 0.2% PA 16:0-18:1. GEF-mediated insulin secretion was not blocked by LPA receptor antagonist.

Conclusion

We determined four characteristics of GEF through lipid analysis and insulin secretion. First, GEF contains a large amount of linoleic acid (C18:2), PA 16:0-18:2, and LPA C18:2 compared with other lipids. Second, the main fatty acid component of LPLs and PLs is linoleic acid (C18:2). Third, GEF stimulates insulin secretion not through LPA receptors. Finally, GEF contains bioactive lipids besides LPAs.

Occurrence of plastidial triacylglycerol synthesis and the potential regulatory role of AGPAT in the model diatom Phaeodactylum tricornutum

BACKGROUND

Microalgae have emerged as a potential feedstock for biofuels and bioactive components. However, lack of microalgal strains with promising triacylglycerol (TAG) content and desirable fatty acid composition have hindered its commercial feasibility. Attempts on lipid overproduction by metabolic engineering remain largely challenging in microalgae.

RESULTS

In this study, a microalgal 1-acyl-sn-glycerol-3-phosphate acyltransferase designated AGPAT1 was identified in the model diatom Phaeodactylum tricornutum. AGPAT1 contained four conserved acyltransferase motifs I-IV. Subcellular localization prediction and thereafter immuno-electron microscopy revealed the localization of AGPAT1 to plastid membranes. AGPAT1 overexpression significantly altered the primary metabolism, with increased total lipid content but decreased content of total carbohydrates and soluble proteins. Intriguingly, AGPAT1 overexpression coordinated the expression of other key genes such as DGAT2 and GPAT involved in TAG synthesis, and consequently increased TAG content by 1.81-fold with a significant increase in polyunsaturated fatty acids, particularly EPA and DHA. Moreover, besides increased lipid droplets in the cytosol, ultrastructural observation showed a number of TAG-rich plastoglobuli formed in plastids.

CONCLUSION

The results suggested that AGPAT1 overexpression could elevate TAG biosynthesis and, moreover, revealed the occurrence of plastidial TAG synthesis in the diatom. Overall, our data provide a new insight into microalgal lipid metabolism and candidate target for metabolic engineering.