Cloning and functional analysis of the FAD2 gene family from desert shrub Artemisia sphaerocephala

Biological Characteristics and Functional Analysis of the Linoleic Acid Synthase Gene ZjFAD2 in Jujube

Jujube fruit is rich in linoleic acid and other bioactive components and has great potential to be used for the development of functional foods. However, the roles of FAD2 genes in linoleic acid biosynthesis in jujube fruit remain unclear. Here, we identified 15 major components in jujube and found that linoleic acid was the main unsaturated fatty acid; major differences in the content and distribution of linoleic acid in the pulp and seeds were observed, and levels of linoleic acid decreased during fruit maturation. Analysis of the fatty acid metabolome, genome, and gene expression patterns of cultivated and wild-type jujube revealed five ZjFAD2 family members highly related to linoleic acid biosynthesis. The heterologous expression of these five ZjFAD2 family members in tobacco revealed that all five of these genes increased the content of linoleic acid. Additionally, transient expression of these genes in jujube fruit and the virus-induced gene silencing (VIGS) test further confirmed the key roles of ZjFAD2-11 and ZjFAD2-1 in the biosynthesis of linoleic acid. The results of this research provide valuable insights into the molecular mechanism underlying linoleic acid synthesis in jujube and will aid the development of quality-oriented breeding strategies.

Engineering Nutritionally Improved Edible Plant Oils

In contrast to traditional breeding, which relies on the identification of mutants, metabolic engineering provides a new platform to modify the oil composition in oil crops for improved nutrition. By altering endogenous genes involved in the biosynthesis pathways, it is possible to modify edible plant oils to increase the content of desired components or reduce the content of undesirable components. However, introduction of novel nutritional components such as omega-3 long-chain polyunsaturated fatty acids needs transgenic expression of novel genes in crops. Despite formidable challenges, significant progress in engineering nutritionally improved edible plant oils has recently been achieved, with some commercial products now on the market.

A mutant cotton fatty acid desaturase 2-1d allele causes protein mistargeting and altered seed oil composition

BACKGROUND

Cotton (Gossypium sp.) has been cultivated for centuries for its spinnable fibers, but its seed oil also possesses untapped economic potential if, improvements could be made to its oleic acid content.

RESULTS

Previous studies, including those from our laboratory, identified pima accessions containing approximately doubled levels of seed oil oleic acid, compared to standard upland cottonseed oil. Here, the molecular properties of a fatty acid desaturase encoded by a mutant allele identified by genome sequencing in an earlier analysis were analyzed. The mutant sequence is predicted to encode a C-terminally truncated protein lacking nine residues, including a predicted endoplasmic reticulum membrane retrieval motif. We determined that the mutation was caused by a relatively recent movement of a Ty1/copia type retrotransposon that is not found associated with this desaturase gene in other sequenced cotton genomes. The mutant desaturase, along with its repaired isozyme and the wild-type A-subgenome homoeologous protein were expressed in transgenic yeast and stably transformed Arabidopsis plants. All full-length enzymes efficiently converted oleic acid to linoleic acid. The mutant desaturase protein produced only trace amounts of linoleic acid, and only when strongly overexpressed in yeast cells, indicating that the missing C-terminal amino acid residues are not strictly required for enzyme activity, yet are necessary for proper subcellular targeting to the endoplasmic reticulum membrane.

CONCLUSION

These results provide the biochemical underpinning that links a genetic lesion present in a limited group of South American pima cotton accessions and their rare seed oil oleic acid traits. Markers developed to the mutant desaturase allele are currently being used in breeding programs designed to introduce this trait into agronomic upland cotton varieties.

Integrated Transcriptome and Metabolome Analysis of Rice Leaves Response to High Saline-Alkali Stress

Rice (Oryza sativa) is one of the most important crops grown worldwide, and saline-alkali stress seriously affects the yield and quality of rice. It is imperative to elucidate the molecular mechanisms underlying rice response to saline-alkali stress. In this study, we conducted an integrated analysis of the transcriptome and metabolome to elucidate the effects of long-term saline-alkali stress on rice. High saline-alkali stress (pH > 9.5) induced significant changes in gene expression and metabolites, including 9347 differentially expressed genes (DEGs) and 693 differentially accumulated metabolites (DAMs). Among the DAMs, lipids and amino acids accumulation were greatly enhanced. The pathways of the ABC transporter, amino acid biosynthesis and metabolism, glyoxylate and dicarboxylate metabolism, glutathione metabolism, TCA cycle, and linoleic acid metabolism, etc., were significantly enriched with DEGs and DAMs. These results suggest that the metabolites and pathways play important roles in rice's response to high saline-alkali stress. Our study deepens the understanding of mechanisms response to saline-alkali stress and provides references for molecular design breeding of saline-alkali resistant rice.

Insights into the Novel FAD2 Gene Regulating Oleic Acid Accumulation in Peanut Seeds with Different Maturity

AhFAD2 is a key enzyme catalyzing the conversion of oleic acid into linoleic acid. The high oleic acid characteristic of peanut mainly comes from the homozygous recessive mutation of AhFAD2A and AhFAD2B genes (aabb). However, even in high-oleic-acid varieties with the aabb genotype, the oleic acid content of seeds with different maturity varies significantly. Therefore, in addition to AhFAD2A and AhFAD2B, other FAD2 members or regulators may be involved in this process. Which FAD2 genes are involved in the regulatory processes associated with seed maturity is still unclear. In this study, four stable lines with different genotypes (AABB, aaBB, AAbb, and aabb) were used to analyze the contents of oleic acid and linoleic acid at different stages of seed development in peanut. Three new AhFAD2 genes (AhFAD2-7, AhFAD2-8, and AhFAD2-9) were cloned based on the whole-genome sequencing results of cultivated peanuts. All peanut FAD2 genes showed tissue preference in expression; however, only the expression level of AhFAD2-7 was positively correlated with the linoleic acid concentration in peanut seeds. These findings provide new insights into the regulation of oleic acid accumulation by maturity, and AhFAD2-7 plays an important role in the maturity dependent accumulation of oleic acid and linoleic acid in peanut.

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.

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.

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.

TILLING-by-Sequencing+ Reveals the Role of Novel Fatty Acid Desaturases (GmFAD2-2s) in Increasing Soybean Seed Oleic Acid Content

Soybean is the second largest source of oil worldwide. Developing soybean varieties with high levels of oleic acid is a primary goal of the soybean breeders and industry. Edible oils containing high level of oleic acid and low level of linoleic acid are considered with higher oxidative stability and can be used as a natural antioxidant in food stability. All developed high oleic acid soybeans carry two alleles; GmFAD2-1A and GmFAD2-1B. However, when planted in cold soil, a possible reduction in seed germination was reported when high seed oleic acid derived from GmFAD2-1 alleles were used. Besides the soybean fatty acid desaturase (GmFAD2-1) subfamily, the GmFAD2-2 subfamily is composed of five members, including GmFAD2-2A, GmFAD2-2B, GmFAD2-2C, GmFAD2-2D, and GmFAD2-2E. Segmental duplication of GmFAD2-1A/GmFAD2-1B, GmFAD2-2A/GmFAD2-2C, GmFAD2-2A/GmFAD2-2D, and GmFAD2-2D/GmFAD2-2C have occurred about 10.65, 27.04, 100.81, and 106.55 Mya, respectively. Using TILLING-by-Sequencing+ technology, we successfully identified 12, 8, 10, 9, and 19 EMS mutants at the GmFAD2-2A, GmFAD2-2B, GmFAD2-2C, GmFAD2-2D, and GmFAD2-2E genes, respectively. Functional analyses of newly identified mutants revealed unprecedented role of the five GmFAD2-2A, GmFAD2-2B, GmFAD2-2C, GmFAD2-2D, and GmFAD2-2E members in controlling the seed oleic acid content. Most importantly, unlike GmFAD2-1 members, subcellular localization revealed that members of the GmFAD2-2 subfamily showed a cytoplasmic localization, which may suggest the presence of an alternative fatty acid desaturase pathway in soybean for converting oleic acid content without substantially altering the traditional plastidial/ER fatty acid production.

Identification, evolution, expression, and docking studies of fatty acid desaturase genes in wheat (Triticum aestivum L.)

Backgrounds

Fatty acid desaturases (FADs) introduce a double bond into the fatty acids acyl chain resulting in unsaturated fatty acids that have essential roles in plant development and response to biotic and abiotic stresses. Wheat germ oil, one of the important by-products of wheat, can be a good alternative for edible oils with clinical advantages due to the high amount of unsaturated fatty acids. Therefore, we performed a genome-wide analysis of the wheat FAD gene family (TaFADs).

Results

68 FAD genes were identified from the wheat genome. Based on the phylogenetic analysis, wheat FADs clustered into five subfamilies, including FAB2, FAD2/FAD6, FAD4, DES/SLD, and FAD3/FAD7/FAD8. The TaFADs were distributed on chromosomes 2A-7B with 0 to 10 introns. The Ka/Ks ratio was less than one for most of the duplicated pair genes revealed that the function of the genes had been maintained during the evolution. Several cis-acting elements related to hormones and stresses in the TaFADs promoters indicated the role of these genes in plant development and responses to environmental stresses. Likewise, 72 SSRs and 91 miRNAs in 36 and 47 TaFADs have been identified. According to RNA-seq data analysis, the highest expression in all developmental stages and tissues was related to TaFAB2.5, TaFAB2.12, TaFAB2.15, TaFAB2.17, TaFAB2.20, TaFAD2.1, TaFAD2.6, and TaFAD2.8 genes while the highest expression in response to temperature stress was related to TaFAD2.6, TaFAD2.8, TaFAB2.15, TaFAB2.17, and TaFAB2.20. Furthermore, docking simulations revealed several residues in the active site of TaFAD2.6 and TaFAD2.8 in close contact with the docked oleic acid that could be useful in future site-directed mutagenesis studies to increase the catalytic efficiency of them and subsequently improve agronomic quality and tolerance of wheat against environmental stresses.

Conclusions

This study provides comprehensive information that can lead to the detection of candidate genes for wheat genetic modification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07199-1.

Transformation and Characterization of Δ12-Fatty Acid Acetylenase and Δ12-Oleate Desaturase Potentially Involved in the Polyacetylene Biosynthetic Pathway from Bidens pilosa

Bidens pilosa is commonly used as an herbal tea component or traditional medicine for treating several diseases, including diabetes. Polyacetylenes have two or more carbon–carbon triple bonds or alkynyl functional groups and are mainly derived from fatty acid and polyketide precursors. Here, we report the cloning of full-length cDNAs that encode Δ12-fatty acid acetylenase (designated BPFAA) and Δ12-oleate desaturase (designated BPOD) from B. pilosa, which we predicted to play a role in the polyacetylene biosynthetic pathway. Subsequently, expression vectors carrying BPFAA or BPOD were constructed and transformed into B. pilosa via the Agrobacterium-mediated method. Genomic PCR analysis confirmed the presence of transgenes and selection marker genes in the obtained transgenic lines. The copy numbers of transgenes in transgenic lines were determined by Southern blot analysis. Furthermore, 4–5 FAA genes and 2–3 OD genes were detected in wild-type (WT) plants. Quantitative real time-PCR revealed that some transgenic lines had higher expression levels than WT. Western blot analysis revealed OD protein expression in the selected transformants. High-performance liquid chromatography profiling was used to analyze the seven index polyacetylenic compounds, and fluctuation patterns were found.