Characterization of the stearoyl-ACP desaturase gene (PoSAD) from woody oil crop Paeonia ostii var. lishizhenii in oleic acid biosynthesis

3-ketoacyl-CoA synthase 7 from Xanthoceras sorbifolium seeds is a crucial regulatory enzyme for nervonic acid biosynthesis

Nervonic acid (C24:1) is a very-long-chain fatty acid that plays an imperative role in human brain development and other health benefits. In plants, 3-ketoacyl-CoA synthase (KCS) is the key rate-limiting enzyme for C24:1 biosynthesis. Xanthoceras sorbifolium is a valuable oil-producing economic woody species with abundant C24:1 in seed oils, but the key KCS gene responsible for C24:1 accumulation remains unknown. In this work, a correlation analysis between the transcript profiles of KCS and dynamic change of C24:1 content in developing seeds of X. sorbifolium were conducted to screen out three members of KCS, namely XsKCS4, XsKCS7 and XsKCS8, potentially involved in C24:1 biosynthesis. Of which, the XsKCS7 was highly expressed in developing seeds, while XsKCS4 and XsKCS8 displayed the highest expression in fruits and flowers, respectively. Overexpression of XsKCS4, XsKCS7 and XsKCS8 in yeast Saccharomyces cerevisiae and plant Arabidopsis thaliana indicated that only XsKCS7 possessed the ability to facilitate the biosynthesis of C24:1. These findings collectively suggested that XsKCS7 played a crucial role in specific regulation of C24:1 biosynthesis in X. sorbifolium seeds.

Analysis of Delta(9) fatty acid desaturase gene family and their role in oleic acid accumulation in Carya cathayensis kernel

Carya cathayensis, commonly referred to as Chinese hickory, produces nuts that contain high-quality edible oils, particularly oleic acid (18:1). It is known that stearoyl-ACP desaturase (SAD) is the first key step converting stearic acid (C18:0, SA) to oleic acid (C18:1, OA) in the aminolevulinic acid (ALA) biosynthetic pathway and play an important role in OA accumulation. Thus far, there is little information about SAD gene family in C. cathayensis and the role of individual members in OA accumulation. This study searched the Chinese Hickory Genome Database and identified five members of SAD genes, designated as CcSADs, at the whole genome level through the comparison with the homologous genes from Arabidopsis. RNA-Seq analysis showed that CcSSI2-1, CcSSI2-2, and CcSAD6 were highly expressed in kernels. The expression pattern of CcSADs was significantly correlated with fatty acid accumulation during the kernel development. In addition, five full-length cDNAs encoding SADs were isolated from the developing kernel of C. cathayensis. CcSADs-green fluorescent protein (GFP) fusion construct was infiltrated into tobacco epidermal cells, and results indicated their chloroplast localization. The catalytic function of these CcSADs was further analyzed by heterologous expression in Saccharomyces cerevisiae, Nicotiana benthamiana, and walnut. Functional analysis demonstrated that all CcSADs had fatty acid desaturase activity to catalyze oleic acid biosynthesis. Some members of CcSADs also have strong substrate specificity for 16:0-ACP to synthesize palmitoleic acid (C16:1, PA). Our study documented SAD gene family in C. cathayensis and the role of CcSSI2-1, CcSSI2-2, and CcSAD6 in OA accumulation, which could be important for future improvement of OA content in this species via genetic manipulation.

Genome-wide analysis of fatty acid desaturase genes in chia (Salvia hispanica) reveals their crucial roles in cold response and seed oil formation

Chia (Salvia hispanica) is a functional food crop with high α-linolenic acid (ALA), the omega-3 essential fatty acid, but its worldwide plantation is limited by cold-intolerance and strict short-photoperiod flowering feature. Fatty acid desaturases (FADs) are responsible for seed oil accumulation, and play important roles in cold stress tolerance of plants. To date, there is no report on systemically genome-wide analysis of FAD genes in chia (ShiFADs). In this study, 31 ShiFAD genes were identified, 3 of which contained 2 alternative splicing transcripts, and they were located in 6 chromosomes of chia. Phylogenetic analysis classified the ShiFAD proteins into 7 groups, with conserved gene structure and MEME motifs within each group. Tandem and segmental duplications coursed the expansion of ShiFAD genes. Numerous cis-regulatory elements, including hormone response elements, growth and development elements, biotic/abiotic stress response elements, and transcription factor binding sites, were predicted in ShiFAD promoters. 24 miRNAs targeting ShiFAD genes were identified at whole-genome level. In total, 15 SSR loci were predicted in ShiFAD genes/promoters. RNA-seq data showed that ShiFAD genes were expressed in various organs with different levels. qRT-PCR detection revealed the inducibility of ShiSAD2 and ShiSAD7 in response to cold stress, and validated the seed-specific expression of ShiSAD11a. Yeast expression of ShiSAD11a confirmed the catalytic activity of its encoded protein, and its heterologous expression in Arabidopsis thaliana significantly increased seed oleic acid content. This work lays a foundation for molecular dissection of chia high-ALA trait and functional study of ShiFAD genes in cold tolerance.

Tung tree stearoyl-acyl carrier protein Δ9 desaturase improves oil content and cold resistance of Arabidopsis and Saccharomyces cerevisiae

The seed oil of tung tree is rich in a-eleostearic acid (ESA), which endows tung oil with the characteristic of an excellently dry oil. The stearoyl-acyl carrier protein δ9 desaturase (SAD) is a rate-limiting enzyme that converts the stearic acid to the oleic acid, the substrate for the production of the α-ESA. However, the function of the two predicted VfSAD1 and VfSAD2 genes in the tung tree has not been determined. In this study, quantitative real-time PCR (qRT-PCR) analysis showed that VfSAD1 and VfSAD2 were expressed in multiple organs of tung tree but were highly expressed in the seed during the oil rapid accumulation period. Heterologous expression of VfSAD1 and VfSAD2 could promote the production of oleic acid and its derivatives in Arabidopsis thaliana and yeast BY4741, indicating that VfSAD1 and VfSAD2 possess the stearoyl-ACP desaturases function. Furthermore, both VfSAD1 and VfSAD2 could significantly improve seed oil accumulation in Arabidopsis. VfSAD1 could also significantly promote the oil accumulation in the yeast BY4741 strain. In addition, overexpression of VfSAD1 and VfSAD2 enhanced the tolerance of yeast and Arabidopsis seedlings to low temperature stress. This study indicates that the two VfSAD genes play a vital role in the process of oil accumulation and fatty acid biosynthesis in the tung tree seed, and both of them could be used for molecular breeding in tung tree and other oil crops.

Progress in understanding and improving oil content and quality in seeds

The world's population is projected to increase by two billion by 2050, resulting in food and energy insecurity. Oilseed crops have been identified as key to address these challenges: they produce and store lipids in the seeds as triacylglycerols that can serve as a source of food/feed, renewable fuels, and other industrially-relevant chemicals. Therefore, improving seed oil content and composition has generated immense interest. Research efforts aiming to unravel the regulatory pathways involved in fatty acid synthesis and to identify targets for metabolic engineering have made tremendous progress. This review provides a summary of the current knowledge of oil metabolism and discusses how photochemical activity and unconventional pathways can contribute to high carbon conversion efficiency in seeds. It also highlights the importance of ¹³C-metabolic flux analysis as a tool to gain insights on the pathways that regulate oil biosynthesis in seeds. Finally, a list of key genes and regulators that have been recently targeted to enhance seed oil production are reviewed and additional possible targets in the metabolic pathways are proposed to achieve desirable oil content and quality.

Characterisation of two novel genes encoding Δ9 fatty acid desaturases (CeSADs) for oleic acid accumulation in the oil-rich tuber of Cyperus esculentus

Cyperus esculentus is considered one of the most promising oil crops due to its oil-rich tuber, wide adaptability and large biomass production. Preferable triacylglycerol (TAG) composition, especially high oleic acid content, makes tuber oil suitable for human consumption and biodiesel production. However, the mechanism underlying oleic acid enrichment in the tuber remains unknown. Plastidial stearoyl-ACP desaturase (SAD) catalyses the formation of monounsaturated fatty acids (MUFAs), which may function crucially for high accumulation of oleic acid in C. esculentus tubers. In this study, two full-length cDNAs encoding SAD were isolated from the developing tubers of C. esculentus, namely, CeSAD1 and CeSAD2, with ORFs of 1194 bp and 1161 bp, respectively. Quantitative RT-PCR analysis showed that CeSAD genes were highly expressed in tubers. The expression pattern during tuber formation was also significantly correlated with fatty acid and oil accumulation dynamics. Overexpression of each CeSAD gene could restore the normal growth of the defective yeast BY4389, indicating that both CeSADs had fatty acid desaturase activity to catalyse MUFA biosynthesis. A tobacco genetic transformation assay demonstrated that both CeSAD enzymes had high enzyme activity. Exogenous addition of exogenous fatty acids to feed yeast revealed that CeSAD1 has a more substantial substrate preference ratio for C18:0 than CeSAD2 did. Moreover, the overexpression of CeSAD1 significantly increased host tolerance against low-temperature stress. Our data add new insights into the deep elucidation of oleic acid-enriched oils in Cyperus esculentus tubers, showing CeSAD, especially CeSAD1, as the target gene in genetic modification to increase oil and oleic yields in oil crops as well as stress tolerance.

Characterization of a novel squalene-rich oil: Pachira macrocarpa seed oil

Pachira macrocarpa is a woody oil crop with high economic and ornamental value. Although P. macrocarpa seeds are rich in oil, little information has been reported about its characterization. In this study, the fatty acids, minor components (tocopherols, squalene, phytosterols, and total phenols), antioxidant activity, cytotoxicity, thermal, and rheological behavior of the P. macrocarpa seed oil (PSO) were investigated for the first time. The results showed that the seeds contained 43.34% lipid, which was mainly composed of palmitic acid (49.96%), linoleic acid (31.22%), and oleic acid (13.48%). The contents of tocopherols, squalene, phytosterols, and total phenols in PSO were 42.01 mg/100 g, 96.78 mg/100 g, 119.67 mg/100 g, and 3.79 mg GAE/100 g, respectively. PSO showed relatively strong DPPH radical scavenging capacity (93.47 µmol TE/100 g) and high melting point (20.8°C). In addition, the oil exhibited Newtonian flow behavior and was not toxic to normal L929 cells at concentrations of 500-8000 µg/ml. As a whole, PSO may be considered as a valuable source for new multipurpose products for industrial utilization. PRACTICAL APPLICATION: Pachira macrocarpa is a woody oil crop and its seeds are rich in oil. Our study has investigated the physicochemical properties and chemical composition of the P. macrocarpa seed oil (PSO). The present study revealed PSO had potential as an edible oil, and it may be considered as a valuable source for new multipurpose products for food industrial utilization.

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.

Expression profiles of genes involved in fatty acid and lipid biosynthesis in developing seeds of Paeonia ostii

BACKGROUND

Paeonia ostii seeds were identified as novel sources of edible plant oil with a high proportion of α-linolenic acid, a type of n-3 fatty acid with many health benefits. Due to the unreliability of seed oil content and quality, it is necessary to discover the mechanism underlying lipid biosynthesis in Paeonia ostii seeds.

OBJECTIVES

This study aimed to identify the key genes involved in lipid biosynthesis in Paeonia ostii seeds by analyzing the relationship among the seed characteristics and the expression patterns of lipid genes in Paeonia ostii during seed development.

METHODS

Preliminary research on Paeonia ostii seed development was carried out from 10 days after pollination until maturity, focusing on phenology, oil content and lipid profiles. In addition, we investigated the spatiotemporal expression of 36 lipid biosynthetic genes in Paeonia ostii by using quantitative real-time PCR.

RESULTS

The results suggested that the development of Paeonia ostii seeds from pollination to maturity could be divided into three periods. The 36 lipid genes showed various spatiotemporal expression patterns and five gene groups with distinct temporal patterns during seed development were identified by clustering analysis of expression data. Furthermore, the relationships between gene expression and lipid/fatty acid accumulation and some candidate key lipid genes were discussed.

CONCLUSIONS

This study provided the global patterns of fatty acid and lipid biosynthesis-related gene expression, which are critical to understanding the molecular basis of lipid biosynthesis and identifying the lipid accumulation rate-limiting genes during seed development.