Functional characterization of two microsomal fatty acid desaturases from Jatropha curcas L

Enolase2 regulates seed fatty acid accumulation via mediating carbon partitioning in Arabidopsis thaliana

In many higher plants, fatty acid (FA) biosynthesis is coordinately regulated at multiple levels by intricate regulatory networks. However, the factors and their regulatory mechanisms underlying seed oil accumulation are still limited. Here, we identified that loss of glycolytic metalloenzyme enolase2 (AtENO2) activity increased the contents of total FAs and salicylic acid (SA) but reduced the accumulation of flavonoids and mucilage by regulating the expression of key genes involved in their biosynthesis pathway in Arabidopsis thaliana seeds. AtENO2 physically interacts with the transcription factor AtTGA5, which may participate in the regulation of SA levels. Non-targeted metabolomics analysis of eno2^- and WT also showed that the levels of three flavonoids, quercetin-3-galactoside, quercitrin, and epicatechin, were significantly decreased in eno2^- , and the flavonoid biosynthesis pathway was also enriched in the KEGG analysis. Meanwhile, the mutation of AtENO2 delayed silique ripening, thereby prolonging silique photosynthesis time, allowing siliques to generate more photosynthesis products for FA biosynthesis. These results reveal a molecular mechanism by AtENO2 to regulate seed oil accumulation in A. thaliana, providing potential targets for improving crop seed oil quality.

Genome sequence and population genomics provide insights into chromosomal evolution and phytochemical innovation of Hippophae rhamnoides

Plants of the Elaeagnaceae family are widely used to treat various health disorders owing to their natural phytochemicals. Seabuckthorn (Hippophae rhamnoides L.) is an economically and ecologically important species within the family with richness of biologically and pharmacologically active substances. Here, we present a chromosome-level genome assembly of seabuckthorn (http://hipp.shengxin.ren/), the first genome sequence of Elaeagnaceae, which has a total length of 849.04 Mb with scaffold N50 of 69.52 Mb and 30 864 annotated genes. Two sequential tetraploidizations with one occurring ~36-41 million years ago (Mya) and the last ~24-27 Mya were inferred, resulting in expansion of genes related to ascorbate and aldarate metabolism, lipid biosynthesis, and fatty acid elongation. Comparative genomic analysis reconstructed the evolutionary trajectories of the seabuckthorn genome with the predicted ancestral genome of 14 proto-chromosomes. Comparative transcriptomic and metabonomic analyses identified some key genes contributing to high content of polyunsaturated fatty acids and ascorbic acid (AsA). Additionally, we generated and analysed 55 whole-genome sequences of diverse accessions, and identified 9.80 million genetic variants in the seabuckthorn germplasms. Intriguingly, genes in selective sweep regions identified through population genomic analysis appeared to contribute to the richness of AsA and fatty acid in seabuckthorn fruits, among which GalLDH, GMPase and ACC, TER were the potentially major-effect causative genes controlling AsA and fatty acid content of the fruit, respectively. Our research offers novel insights into the molecular basis underlying phytochemical innovation of seabuckthorn, and provides valuable resources for exploring the evolution of the Elaeagnaceae family and molecular breeding.

Overexpression of PvFAD3 Gene from Plukenetia volubilis Promotes the Biosynthesis of α-Linolenic Acid in Transgenic Tobacco Seeds

The ω-3 fatty acid desaturase (FAD3) gene encodes a rate-limiting enzyme in the synthesis of α-linolenic acid. In this study, homologous cloning was used to obtain the full-length sequence of the PvFAD3 gene of Plukenetia volubilis. The full-length DNA sequence was 1871 bp long, with 8 exons and 7 introns. The structural analysis of the amino acid sequence revealed that the PvFAD3 protein contained three histidine-conserved regions and an endoplasmic reticulum retention signal. The real-time reverse transcription-polymerase chain reaction performed for determining the expression patterns of the PvFAD3 gene in different tissues of P. volubilis showed that PvFAD3 expression was highly expressed in the fast oil accumulation stage of seed. The analysis of subcellular localization assay in epidermal cells of tobacco (Nicotiana benthamiana) leaves showed that the PvFAD3 protein was mainly localized in the endoplasmic reticulum. Seed-specific overexpression vectors were constructed, and Agrobacterium-mediated genetic transformation was performed to obtain transgenic tobacco plants overexpressing PvFAD3. The results of fatty acid assays performed using harvested seeds showed a significant increase in α-linolenic acid content, a dramatic decrease in linoleic acid content, and an obvious increase in oil content in transgenic tobacco seeds. Collectively, the PvFAD3 gene of P. volubilis was confirmed as a key enzyme gene for α-linolenic acid synthesis; thus, indicating that the PvFAD3 gene can be used for fatty acid fraction improvement in oilseed plants.

Characterization of genes encoding ω-6 desaturase PoFAD2 and PoFAD6, and ω-3 desaturase PoFAD3 for ALA accumulation in developing seeds of oil crop Paeonia ostii var. lishizhenii

Paeonia ostii var. lishizhenii has emerged as a valuable oil-producing crop with splendid characteristic of high α-linolenic acid (C18:3, ALA) content in its seed oil for healthy food supplement, but the molecular mechanism for seed ALA accumulation remains enigmatic. In our previous report, a PoSAD gene encoding stearoyl-ACP desaturase had been cloned and functional charactered for the first desaturation procedure involved in ALA biosynthesis pathway in P. ostii var. lishizhenii endosperms, while other participants have not been identified to date. In this study, full-length cDNAs of PoFAD2 (1489 bp), PoFAD6 (1638 bp), and PoFAD3 (1709 bp) were isolated based on our recent transcriptome sequencing data. Bioinformatic analyses revealed that the PoFADs were closest to their counterparts from Paeoniaceae species P. ludlowii, P. rockii, and P. suffruticosa in phylogenetic tree, which shared highly conserved histidine boxes (HXXXH, HXXHH, and HXXHH), exhibiting typical characters of membrane-bound desaturases in higher plants. Additionally, the PoFAD2 and PoFAD3 were specifically expressed and highly associated with LA and ALA accumulation in developing endosperms, whereas PoFAD6 expression has no significantly difference during whole seed developing stages. The catalytic function of these PoFADs were further analyzed by heterologous expression in Saccharomyces cerevisiae and Arabidopsis thaliana. The results showed that PoFAD2 and PoFAD6 could catalyze linoleic acid (C18:2) synthesis, while PoFAD3 had ability to produce ALA. This study functional identified three PoFAD genes, which indicates their critical roles in ALA biosynthesis pathway in P. ostii var. lishizhenii, and is of great theoretical and practical meaning on breeding and cultivating new tree peony varieties to promote human health and nutrition supplement.

Linum usitatissimum FAD2A and FAD3A enhance seed polyunsaturated fatty acid accumulation and seedling cold tolerance in Arabidopsis thaliana

Flax (Linum usitatissimum) seed oil is rich in polyunsaturated fatty acids (PUFAs), particularly linolenic acid, which is converted from linoleic acid. Studies have indicated that the biosynthesis of linoleic acid and linolenic acid is controlled by FAD2 and FAD3, respectively. However, the functional distinctions of different LuFAD2 and LuFAD3 copies from L. usitatissimum in governing the biosynthesis of linoleic acid or linolenic acid, respectively, remain unclear. In this study, five LuFAD2 and three LuFAD3 cDNAs were cloned from the L. usitatissimum cultivar 'Longya 10', and GC-MS results demonstrated that LuFAD2A and LuFAD3A play predominant roles in the accumulation of linoleic acid and linolenic acid, respectively. Their simultaneous overexpression in Arabidopsis thaliana seeds led to a significant increase in fatty acid contents, especially PUFAs. Additionally, LuFAD2A and LuFAD3A promoted the biosynthesis of jasmonic acid by increasing the levels of linolenic acid, which, in turn, enhanced plant cold tolerance. When the amount of linolenic acid is not sufficient, plants adapt to low temperature via the accumulation of anthocyanins. These findings provide insights into the higher accumulation of PUFAs in L. usitatissimum seeds, and provide potential targets for improving oil quality of other oil-producing crops through molecular manipulation.

Functional characterization and expression profile of microsomal FAD2 and FAD3 genes involved in linoleic and α-linolenic acid production in Leucas cephalotes

The genus Leucas belongs to Lamiaceae, and has attained more attention due to the presence of unusual allenic fatty acids called laballenic and phlomic acid in majority of its species. This genus has been known since traditional medicinal times and has numerous economical, nutritional, and industrial properties. So far genetic, molecular and biochemical analyses of lipid metabolism and fatty acid biosynthetic pathway in Leucas has not been reported. The objective of this study is to identify, isolate, analyze expression profiles, and functionally characterize the membrane-associated desaturases responsible for unsaturated fatty acid accumulation in Leucas cephalotes. Full-length LcFAD2 and LcFAD3 cDNAs were isolated and expressed in Saccharomyces cerevisiae BY4741 for functional characterization. Substrate feeding assay using S. cerevisiae confirmed that the LcFAD2 enzyme catalyzes desaturation of both palmitoleic (16:1∆⁹) and oleic (18:1∆⁹) acids to form palmitolinoleic (16:2∆^9,12) and linoleic (18:2∆^9,12) acids respectively. As a contrast, the heterologous activity of LcFAD2 enzyme in S. cerevisiae led to the synthesis of palmitolinoleic (16:2∆^9,12) acid, an unusual fatty acid that is not found naturally in Leucas cephalotes. While the LcFAD3 enzyme catalyzed linoleic acid (18:2∆^9,12) into α-linolenic acid (18:3∆^9,12,15). Furthermore, transcript abundance of LcFAD2 and LcFAD3 cDNAs were estimated from various plant parts such as roots, shoots, leaves, petals and developing seeds. Our results have shown that the differential transcriptional activity of LcFAD2 and LcFAD3 desaturase genes differs significantly in developing seeds, petals, leaves, stems, and roots of L. cephalotes. Furthermore, for the industrial production of these essential fatty acids, namely, linoleic and α-linolenic acid, FAD2 and FAD3 enzyme activity could be exploited from this upcoming significant oil plant, Leucas cephalotes.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01016-z.

Isolation and functional analyses of PvFAD2 and PvFAD3 involved in the biosynthesis of polyunsaturated fatty acids from Sacha Inchi (Plukenetia volubilis)

The development of ω-3 fatty acid-rich vegetable oils is essential to enrich the production of functional foods. Sacha Inchi (Plukenetia volubilis L.) is a unique oilseed crop with much potential. Its seeds contain rich polyunsaturated fatty acids (PUFAs), especially linoleic acid (LA, C18:2) and α-linolenic acid (ALA, C18:3). Endoplasmic reticulum -located ω-6 and ω-3 fatty acid desaturases (FAD) are responsible for the biosynthesis of LA and ALA, respectively, in plant seeds. Here, we isolated two full-length FAD genes from Sacha Inchi, named PvFAD2 and PvFAD3, which encoded predicted amino acid residues of 384 and 379 in protein, respectively. Protein sequence and subcellular localization analysis revealed that they were located in the endoplasmic reticulum (ER). Heterologous expression in Saccharomyces cerevisiae confirmed that PvFAD2 and PvFAD3 could catalyze LA and ALA synthesis, respectively. The stability and catalytic efficiency of the PvFAD3 protein may be closely related to temperature. In transgenic tobacco, using seed-specific expression promoters, PvFAD2 and PvFAD3 significantly promotes the production of LA (from 68% to 70.5%) and ALA (from 0.7% to 3.1%) in seed oil. These results show that PvFAD2 and PvFAD3 do, indeed, function as crucial enzymes for PUFAs biosynthesis, and provide a key gene source for the sustainable production of lipids with tailored fatty acid compositions via genetic engineering in other oil crops.

Design of high-oleic tobacco (Nicotiana tabacum L.) seed oil by CRISPR-Cas9-mediated knockout of NtFAD2-2

BACKGROUND

Tobacco seed oil could be used as an appropriate feedstock for biodiesel production. However, the high linoleic acid content of tobacco seed oil makes it susceptible to oxidation. Altering the fatty acid profile by increasing the content of oleic acid could improve the properties of biodiesel produced from tobacco seed oil.

RESULTS

Four FAD2 genes, NtFAD2-1a, NtFAD2-1b, NtFAD2-2a, and NtFAD2-2b, were identified in allotetraploid tobacco genome. Phylogenetic analysis of protein sequences showed that NtFAD2-1a and NtFAD2-2a originated from N. tomentosiformis, while NtFAD2-1b and NtFAD2-2b from N. sylvestris. Expression analysis revealed that NtFAD2-2a and NtFAD2-2b transcripts were more abundant in developing seeds than in other tissues, while NtFAD2-1a and NtFAD2-1b showed low transcript levels in developing seed. Phylogenic analysis showed that NtFAD2-2a and NtFAD2-2b were seed-type FAD2 genes. Heterologous expression in yeast cells demonstrated that both NtFAD2-2a and NtFAD2-2b protein could introduce a double bond at the Δ12 position of fatty acid chain. The fatty acid profile analysis of tobacco fad2-2 mutant seeds derived from CRISPR-Cas9 edited plants showed dramatic increase of oleic acid content from 11% to over 79%, whereas linoleic acid decreased from 72 to 7%. In addition, the fatty acid composition of leaf was not affected in fad2-2 mutant plants.

CONCLUSION

Our data showed that knockout of seed-type FAD2 genes in tobacco could significantly increase the oleic acid content in seed oil. This research suggests that CRISPR-Cas9 system offers a rapid and highly efficient method in the tobacco seed lipid engineering programs.

Identification and functional characterization of Buglossoides arvensis microsomal fatty acid desaturation pathway genes involved in polyunsaturated fatty acid synthesis in seeds

Buglossoides arvensis seed oil is the richest natural source of stearidonic acid (SDA), an ω-3 fatty acid with nutraceutical potential superior to α-linolenic acid (ALA). The molecular basis of polyunsaturated fatty acid synthesis in B. arvensis is unknown. Here, we describe the identification of B. arvensis fatty acid desaturase2 (BaFAD2), fatty acid desaturase3 (BaFAD3), and Delta-6-desaturase (BaD6D-1 and BaD6D-2) genes by mining the transcriptome of developing seeds and their functional characterization by heterologous expression in Saccharomyces cerevisiae. In silico analysis of their encoded protein sequences showed conserved histidine-boxes and signature motifs essential for desaturase activity. Expression profiling of these genes showed higher transcript abundance in reproductive tissues than in vegetative tissues, and their expression varied with temperature stress treatments. Yeast expressing BaFAD2 was found to desaturate both oleic acid and palmitoleic acid into linoleic acid (LA) and hexadecadienoic acid, respectively. Fatty acid supplementation studies in yeast expressing BaFAD3 and BaD6D-1 genes revealed that the encoded enzyme activities of BaFAD3 efficiently converted LA to ALA, and BaD6D-1 converted LA to γ-linolenic acid and ALA to SDA, but with an apparent preference to LA. BaD6D-2 did not show the encoded enzyme activity and is not a functional D6D. Our results provide an insight into SDA biosynthesis in B. arvensis and expand the repository of fatty acid desaturase targets available for biotechnological production of SDA in traditional oilseed crops.

Molecular cloning and function analysis of FAD2 gene in Idesia polycarpa

Idesia polycarpa is a valuable oil-producing tree and can potentially be used for edible oil and biofuel production. The fruits of I. polycarpa are unique in that they contain both saturated and unsaturated lipids. Fatty acid desaturase 2 (FAD2), also as known as omega-6 fatty acid desaturase in endoplasmic, is a key enzyme for linoleic acid and α-linolenic acid biosynthesis. However, bioinformatics and expression of FAD2 in I. polycarpa are still absent. Here, to gain insight into the lipid and linoleic synthesis of I. polycarpa, we compared the fruits from different growth stages. Lipid accumulation rates, final lipid content, linoleic accumulation rates and final linoleic content were significantly different among the different stages. In a further step, the FAD2 gene from fruits of I. polycarpa, named IpFAD2, was cloned and characterized. A partial fragment of 169 bp of IpFAD2 was amplified by degenerate PCR. Full cDNA of IpFAD2 was obtained by the RACE technique. The open-reading frame of IpFAD2 was 1149 bp in length, encoding 382 amino acids. A comparison of the deduced amino acids sequence of IpFAD2 with FAD2 from other species showed high similarities, ranging from 78.8 to 92.6%. The IpFAD2-predicted protein has a theoretical molecular mass of 44.03 kDa and an isoelectric point (pI) of 8.04. It has five transmembrane helices located on the endoplasmic reticulum. The IpFAD2-predicted protein was classified as belonging to the Membrane-FADS-like superfamily based on its conserved domain analysis. Expression analysis based on qRT-PCR indicated that IpFAD2 was expressed in different fruit growth stages, with the highest expression level at 80 DAP and the lowest at 130 DAP. The expression of IpFAD2 was positively correlated with the linoleic accumulation rates in I. polycarpa fruits. Prokaryotic expression in Escherichia. Coli BL21(DE3) indicated that IpFAD2 gene could encode a bio-functional omega-6 fatty acid desaturase. Heterologous expression in Arabidopsis thaliana confirmed that the isolated IpFAD2 proteins could catalyse linoleic synthesis. This is the first cloning and expression analysis of FAD2 from I. polycarpa, significantly contributing to our understanding of the role of IpFAD2 in linoleic synthesis, esp. in terms of genetic engineering breeding for linoleic production.

Endoplasmic reticulum retention signaling and transmembrane channel proteins predicted for oilseed ω3 fatty acid desaturase 3 (FAD3) genes

Oilseed crop oils contain a variety of unsaturated fatty acids that are synthesized and regulated by fatty acid desaturases (FADs). In this study, 14 FAD3 (ω3 desaturase) protein sequences from oilseeds are analyzed and presented through the application of several computational tools. The results indicated a close relationship between Brassica napus and Camelina sativa, as well as between Salvia hispanica and Perilla frutescens FAD3s, due to a high similarity in codon preferences in codon usage clusters and the phylogenetic tree. The cis-acting element results reveal that the seed-specific promoter region of BnFAD3 contains the critical conserved boxes such as HSE and ABRE, which are involved in responsiveness to heat stress and abscisic acid. The presence of the aforementioned conserved boxes may increase cold acclimation as well as tolerance to drought and high salinity. Omega(ω)3 desaturases contain a Skn-1 motif which is a cis-acting regulatory element required involved in endosperm development. In oilseed FAD3s, leucine is the most repeated amino acid in FAD3 proteins. The study conveyed that B. napus, Camelina sativa, Linum usitatissimum, Vernicia fordii, Gossypium hirsutum, S. hispanica, Cannabis sativa, and P. frutescens have retention signal KXKXX/XKXX at their c-terminus sites, which is one of the most important characteristics of FADs. Additionally, it was found that BnFAD3 is a transmembrane protein that can convert ω6 to ω3 fatty acids and may simultaneously act as a potassium ion channel in the ER.

Strong co-suppression impedes an increase in polyunsaturated fatty acids in seeds overexpressing FAD2

Fatty acid desaturase2 (FAD2) catalyses the conversion of oleic acid to linoleic acid and is the main determinant of the levels of essential poly-unsaturated fatty acids (PUFAs) in seed oils. The very limited number of successful examples of overexpression of FAD2 over the last two decades and a shortage of reports on co-suppression make it uncertain whether FAD2 can increase PUFAs effectively across a broad range of oil crops. In this study, strong co-suppression was observed in about 80% of over 100 transgenic lines when FAD2 was overexpressed in three oilseed crops, namely flax (Linum usitatissimum), carinata (Brassica carinata), and camelina (Camelina sativa), as well as in the model plant Arabidopsis. Further analyses of Arabidopsis transgenic lines revealed both endogenous and transgenic FAD2 gene-silencing. Thus, the commonality and potency of FAD2 co-suppression seemingly imposes an obstacle to engineering oilseed PUFA enhancement by direct FAD2 overexpression. AtFAD2, driven by the 35S promoter, also caused co-suppression in Arabidopsis roots. The FAD2 co-suppression was unstable and PUFA phenotypes of T4 lines were similar to the wild-type, further indicating that high PUFA content cannot be achieved by screening advanced generations. However, we demonstrate that the obstacle of FAD2 co-suppression can be overcome in the Arabidopsis rdr6 mutant, which is impaired in post-transcriptional gene-silencing, and that lines with high PUFA content are stable through four generations.

Fatty acid desaturase 3 (PsFAD3) from Paeonia suffruticosa reveals high α-linolenic acid accumulation

α-linolenic acid (ALA) deficiency and a skewed ω6: ω3 fatty acid ratio in the diet are thought to be a major cause for the high incidence of cardiovascular, inflammatory, and autoimmune diseases. Recent years, tree peony (Paeonia suffruticosa Andr.) with the high proportion of ALA (more than 45% in seed oil) is widely concerned. However, the underlying accumulation mechanism of the ALA in tree peony seeds remains unknown. In this study, comparative transcriptome analysis was performed between two cultivars ('Saiguifei' and 'Jingshenhuanfa') with different ALA contents. The analysis of the metabolic enzymes associated with ALA biosynthesis and temporal accumulation patterns of unsaturated fatty acids demonstrated the importance of microsomal ω-3 fatty acid desaturase 3 (FAD3). Moreover, PsFAD3 gene was identified from tree peony seeds, which was located in endoplasmic reticulum and the expression levels of PsFAD3 were consistent with ALA accumulation patterns in seeds. Heterologous expression in Saccharomyces cerevisiae and Arabidopsis thaliana confirmed that the isolated PsFAD3 protein could catalyze ALA synthesis. These results indicated that PsFAD3 was involved in the synthesis of ALA in seeds and could be exploited by the genetic breeding of new cultivars with high ALA content in tree peony as well as other potential crops.

Molecular cloning and characterization of two β-ketoacyl-acyl carrier protein synthase I genes from Jatropha curcas L

The β-ketoacyl-acyl carrier protein synthase I (KASI) is involved in de novo fatty acid biosynthesis in many organisms. Two putative KASI genes, JcKASI-1 and JcKASI-2, were isolated from Jatropha curcas. The deduced amino acid sequences of JcKASI-1 and JcKASI-2 exhibit around 83.8% and 72.5% sequence identities with AtKASI, respectively, and both contain conserved Cys-His-Lys-His-Phe catalytic active sites. Phylogenetic analysis indicated that JcKASI-2 belongs to a clade with several KASI proteins from dicotyledonous plants. Both JcKASI genes were expressed in multiple tissues, most strongly in filling stage seeds of J. curcas. Additionally, the JcKASI-1 and JcKASI-2 proteins were both localized to the plastids. Expressing JcKASI-1 in the Arabidopsis kasI mutant rescued the mutant's phenotype and restored the fatty acid composition and oil content in seeds to wild-type, but expressing JcKASI-2 in the Arabidopsis kasI mutant resulted in only partial rescue. This implies that JcKASI-1 and JcKASI-2 exhibit partial functional redundancy and KASI genes play a universal role in regulating fatty acid biosynthesis, growth, and development in plants.

Differential Contribution of Endoplasmic Reticulum and Chloroplast ω-3 Fatty Acid Desaturase Genes to the Linolenic Acid Content of Olive (Olea europaea) Fruit

Linolenic acid is a polyunsaturated fatty acid present in plant lipids, which plays key roles in plant metabolism as a structural component of storage and membrane lipids, and as a precursor of signaling molecules. The synthesis of linolenic acid is catalyzed by two different ω-3 fatty acid desaturases, which correspond to microsomal- (FAD3) and chloroplast- (FAD7 and FAD8) localized enzymes. We have investigated the specific contribution of each enzyme to the linolenic acid content in olive fruit. With that aim, we isolated two different cDNA clones encoding two ω-3 fatty acid desaturases from olive (Olea europaea cv. Picual). Sequence analysis indicates that they code for microsomal (OepFAD3B) and chloroplast (OepFAD7-2) ω-3 fatty acid desaturase enzymes, different from the previously characterized OekFAD3A and OekFAD7-1 genes. Functional expression in yeast of the corresponding OepFAD3A and OepFAD3B cDNAs confirmed that they encode microsomal ω-3 fatty acid desaturases. The linolenic acid content and transcript levels of olive FAD3 and FAD7 genes were measured in different tissues of Picual and Arbequina cultivars, including mesocarp and seed during development and ripening of olive fruit. Gene expression and lipid analysis indicate that FAD3A is the gene mainly responsible for the linolenic acid present in the seed, while FAD7-1 and FAD7-2 contribute mostly to the linolenic acid present in the mesocarp and, therefore, in the olive oil. These results also indicate the relevance of lipid trafficking between the endoplasmic reticulum and chloroplast in determining the linolenic acid content of membrane and storage lipids in oil-accumulating photosynthetic tissues.

Identification and expression of a stearoyl-ACP desaturase gene responsible for oleic acid accumulation in Xanthoceras sorbifolia seeds

Xanthoceras sorbifolia Bunge is an oilseed tree that grows well on barren lands in dry climate. Its seeds contain a large amount of oil rich in oleic acid (18:1(Δ9)) and linoleic acid (18:2(Δ9, 12)). However, the molecular regulation of oil biosynthesis in X. sorbifolia seeds is poorly understood. Stearoyl-ACP desaturase (SAD, EC 1.14.99.6) is a plastid-localized soluble desaturase that catalyzes the conversion of stearic acid (18:0) to oleic acid, which plays a key role in determining the ratio of saturated to unsaturated fatty acids. In this study, a full-length cDNA of XsSAD was isolated from developing X. sorbifolia embryos. The XsSAD open reading frame had 1194-bp, encoding a polypeptide of 397 amino acids. XsSAD expression in Escherichia coli cells resulted in increased 18:1(Δ9) level, confirming the biological activity of the enzyme encoded by XsSAD. XsSAD expression in Arabidopsis ssi2 mutants partially restored the morphological phenotype and effectively increased the 18:1(Δ9) level. The levels of other unsaturated fatty acids synthesized with 18:1(Δ9) as the substrate also increased to some degree. XsSAD in X. sorbifolia had a much higher expression in embryos than in leaves and petals. XsSAD expression also correlated well with the oleic acid, unsaturated fatty acid, and total fatty acid levels in developing embryos. These data suggested that XsSAD determined the synthesis of oleic acid and contributed to the accumulation of unsaturated fatty acid and total oil in X. sorbifolia seeds. A preliminary tobacco rattle virus-based virus-induced gene silencing system established in X. sorbifolia can also be helpful for further analyzing the functions of XsSAD and other oil synthesis-related genes in woody plants.

Global analysis of gene expression profiles in physic nut (Jatropha curcas L.) seedlings exposed to drought stress

BACKGROUND

Physic nut (Jatropha curcas L.) is a small perennial tree or large shrub, which is well-adapted to semi-arid regions and is considered to have potential as a crop for biofuel production. It is now regarded as an excellent model for studying biofuel plants. However, our knowledge about the molecular responses of this species to drought stress is currently limited.

RESULTS

In this study, genome-wide transcriptional profiles of roots and leaves of 8-week old physic nut seedlings were analyzed 1, 4 and 7 days after withholding irrigation. We observed a total of 1533 and 2900 differentially expressed genes (DEGs) in roots and leaves, respectively. Gene Ontology analysis showed that the biological processes enriched in droughted plants relative to unstressed plants were related to biosynthesis, transport, nucleobase-containing compounds, and cellular protein modification. The genes found to be up-regulated in roots were related to abscisic acid (ABA) synthesis and ABA signal transduction, and to the synthesis of raffinose. Genes related to ABA signal transduction, and to trehalose and raffinose synthesis, were up-regulated in leaves. Endoplasmic reticulum (ER) stress response genes were significantly up-regulated in leaves under drought stress, while a number of genes related to wax biosynthesis were also up-regulated in leaves. Genes related to unsaturated fatty acid biosynthesis were down-regulated and polyunsaturated fatty acids were significantly reduced in leaves 7 days after withholding irrigation. As drought stress increased, genes related to ethylene synthesis, ethylene signal transduction and chlorophyll degradation were up-regulated, and the chlorophyll content of leaves was significantly reduced by 7 days after withholding irrigation.

CONCLUSIONS

This study provides us with new insights to increase our understanding of the response mechanisms deployed by physic nut seedlings under drought stress. The genes and pathways identified in this study also provide much information of potential value for germplasm improvement and breeding for drought resistance.

Over-expression of JcDGAT1 from Jatropha curcas increases seed oil levels and alters oil quality in transgenic Arabidopsis thaliana

The increasing consumption of fossil fuels and petroleum products is leading to their rapid depletion and is a matter of concern around the globe. Substitutes of fossil fuels are required to sustain the pace of economic development. In this context, oil from the non food crops (biofuel) has shown potential to substitute fossil fuels. Jatropha curcas is an excellent shrub spread and naturalized across the globe. Its oil contains a high percentage of unsaturated fatty acids (about 78-84% of total fatty acid content) making the oil suitable for biodiesel production. Despite its high oil content, it has been poorly studied in terms of important enzymes/genes responsible for oil biosynthesis. Here, we describe the isolation of the full length cDNA clone of JcDGAT1, a key enzyme involved in oil biosynthesis, from J. curcas seeds and manipulation of oil content and composition in transgenic Arabidopsis plants by its expression. Transcript analysis of JcDGAT1 reveals a gradual increase from early seed development to its maturation. Homozygous transgenic Arabidopsis lines expressing JcDGAT1 both under CaMV35S promoter and a seed specific promoter show an enhanced level of total oil content (up by 30-41%) in seeds but do not show any phenotypic differences. In addition, our studies also show alterations in the oil composition through JcDGAT1 expression. While the levels of saturated FAs such as palmitate and stearate in the oil do not change, there is significant reproducible decrease in the levels of oleic acid and a concomitant increase in levels of linolenic acid both under the CaMV35S promoter as well as the seed specific promoter. Our studies thus confirm that DGAT is involved in flux control in oil biosynthesis and show that JcDGAT1 could be used specifically to manipulate and improve oil content and composition in plants.