Characterization of diacylglycerol acyltransferase 2 from Idesia polycarpa and function analysis

De novo assembly of Idesia polycarpa transcriptome and unsaturated fatty acid biosynthesis candidate genes Mining and functional Identification

Unsaturated fatty acids (UFA) in lipids are the key to nutraceutical oil applications, with various potential applications in nutraceutical functional foods and pharmaceutical industries. In Idesia polycarpa (Salicaceae), more than 80 % of UFA have been found in the fruits; yet, the underlying genetic mechanism remains poorly understood. Due to the lack of theoretical research on the genes related to lipid biosynthesis and the complete genetic transformation system of I. polycarpa fruit, the selection and breeding of I. polycarpa, an excellent oil tree, has been severely restricted. In-depth understanding of the molecular mechanism and gene function of lipid biosynthesis of I. polycarpa fruit is therefore of great significance for the development of I. polycarpa resources. This is not only conducive to the genetic improvement of I. polycarpa by molecular breeding technologies but can also provide a reference for the study of the gene functions of other oil plants. In this study, the FA accumulation patterns of I. polycarpa fruits during 8 growth periods were analysed. Fruit from two developmental periods with different UFA levels were analysed for RNA sequencing by an Illumina NovaSeq 6000 HiSeq platform. De novo transcriptome assembly presented 115,350 unigenes and 4382 differentially expressed genes (DEGs). Functional annotation in the KEGG pathway and combined with DEG data revealed candidate genes potentially involved in UFA biosynthesis. Expression analysis of q-PCR of IpDGAT2, IpGPAT, IpKASII, IpSAD, IpFAD2, IpFAD3 and IpFAD8 suggested that these genes are highly involved in UFA biosynthesis. Full-length candidate genes were cloned and analysed by bioinformatic tools, and function analysis of IpSAD and IpFAD3 showed that these genes regulated the products of linoleic acid metabolism. This study provides a foundation for UFA biosynthesis in Idesia polycarpa, facilitating its genetic breeding in the future.

Subchronic Toxicity Evaluation of Idesia polycarpa Fruit Oil by 90-Day Oral Exposure in Wistar Rats

Idesia polycarpa, belonging to the Flacourtiaceae family, is a tall deciduous tree, widely distributed in some Asian countries. It is famous for its high yield of fruit known as oil grape, which is rich of linoleic acid and linolenic acid, and so on. To provide evidences for its safe use as food, subchronic toxicity of I. polycarpa fruit oil and no observed adverse effect level were performed in male and female specific pathogen-free Wistar rats. Based on the Organization for Economic Co-operation and Development guidelines, the oil was orally administered to rats by gavage at 0, 1.0, 2.0, and 4.0mL/kg.bw/day for 90 days, followed by a 28-day recovery period. The results showed that no sign of oil-related toxicity, clinically or histologically, was observed in both male and female rats. Although there was a slight increase or decrease in some indicators such as hematology, serum chemistry, and so on, those changes were all within the normal ranges, and as presented in the 90-day study, the oil exhibited no toxic effect compared to the control rats. I. polycarpa might be a potential excellent and healthy vegetable oil resource.

An investigation of the growth status of 19-year-old Idesia polycarpa 'Yuji' plantation forest in the mountainous region of Henan, China

Plantation forests play an important role in the mitigation of greenhouse gas emissions. Idesia polycarpa Maxim is an emerging woody oil tree species in most Asian countries. The 19-year-old Idesia polycarpa 'Yuji' plantation forest was selected as a sample site. The nutrient contents of the understory soil total carbon (TC), total nitrogen (TN), nitrate nitrogen (NN), organic carbon (OC), available phosphorus (AP), available potassium (AK), and pH were analyzed. Several metrics were measured to quantify the growth status of the forest, such as tree heights (H), clear bole heights (CBH), diameters at breast height (DBH), and male-to-female ratios (MFR). In addition, we harvested the fruits to analyze oil content and fatty acid composition. The results found that the nutrient content of the soil was TC (4.93%), TN (0.42%), NN (43.08 mg kg-1), OC (4.90 g kg-1), AP (13.66 mg kg-1), AK (30.48 mg kg-1), and pH (7.90). The growth characteristics were H (11.75 m), DBH (12.79 cm), and CBH (6.17 m). The MFR was close to 1:1. Besides, the oil content of the fruit and unsaturated fatty acids was 24.08% and 68.49%, respectively. As an alternative tree species, the plantation of Idesia polycarpa offers great potential in artificial afforestation in some particular places with specific forest site conditions.

Molecular regulation of lipid metabolism in Suaeda salsa

Suaeda salsa is remarkable for its high oil content and abundant unsaturated fatty acids. In this study, the regulatory networks on fatty acid and lipid metabolism were constructed by combining the de novo transcriptome and lipidome data. Differentially expressed genes (DEGs) associated with lipids biosynthesis pathways were identified in the S. salsa transcriptome. DEGs involved in fatty acid and glycerolipids were generally up-regulated in leaf tissues. DEGs for TAG assembly were enriched in developing seeds, while DEGs in phospholipid metabolic pathways were enriched in root tissues. Polar lipids were extracted from S. salsa tissues and analyzed by lipidomics. The proportion of galactolipid MGDG was the highest in S. salsa leaves. The molar percentage of PG was high in the developing seeds, and the other main phospholipids had higher molar percentage in roots of S. salsa. The predominant C36:6 molecular species indicates that S. salsa is a typical 18:3 plant. The combined transcriptomic and lipidomic data revealed that different tissues of S. salsa were featured with DEGs associated with specific lipid metabolic pathways, therefore, represented unique lipid profiles. This study will be helpful on understanding lipid metabolism pathway and exploring the key genes involved in lipid synthesis in S. salsa.

Newly identified essential amino acids affecting peanut (Arachis hypogaea L.) DGAT2 enzyme activity

Triacylglycerols is the major storage lipid in most crop seeds. As the key enzyme catalyzing the final step of triacylglycerols biosynthesis, the activity of diacylglycerol acyltransferases directly related to oil content. It has been shown that certain amino acids are very important for enzyme activity, one amino acid variation will greatly change the enzyme activity. In this study, we identified three amino acid point mutations that affect the Arachis hypogaea diacylglycerol acyltransferase 2 enzyme activity, T107M, K251R and L316P. According to the three amino acid variations, three single-nucleotide-mutant sequences of Arachis hypogaea diacylglycerol acyltransferase 2a were constructed and transformed into yeast strain H1246 for function verification. Results showed that T107M and K251R could change the fatty acid content and composition of the transformed yeast strains, whereas L316P led to the loss of enzyme activity. By analyzing the 2D and 3D structures of the three variants, we found that the changes of spatial structure of T107M, K251R and L316P caused the changes of the enzyme activity. Our study could provide a theoretical basis for changing the enzyme activity of DGAT by genetic engineering, and provide a new idea for increasing the oil content of the crops.

Genome-wide analysis of DGAT gene family in Perilla frutescens and functional characterization of PfDGAT2-2 and PfDGAT3-1 in Arabidopsis

Diacylglycerol acyltransferase (DGAT) is the rate-limiting enzyme that catalyzes the final step in triacylglycerol biosynthesis, however, members of DGAT gene family of Perilla frutescens has not yet been identified and characterized. In this study, a total of 20 PfDGAT genes were identified from the genome of Perilla frutescens and were divided into four groups (PfDGAT1, PfDGAT2, PfDGAT3, PfWS/DGAT) according to their phylogenetic relationships. These were unevenly distributed across the 12 chromosomes. Sequence analysis revealed that PfDGAT members of the same subfamily have highly conserved gene structures, protein motifs and cis-acting elements in their promoters. Gene duplication analysis showed that random duplication and segmental duplication contributed to the expansion of the DGAT family in P. frutescens. RNA-seq and qRT-PCR analysis suggested that they may play a role in the growth and development of Perilla, especially in the accumulation of seed oil. Compared with the wild-type, seed length, width, and 1000-seed weight of transgenic PfDGAT2-2 and PfDGAT3-1 Arabidopsis were significantly increased, as well as the seed oil content increased by 7.36-15.83 %. Over-expression of PfDGAT2-2 could significantly increase the content of C18:3 and C20:1 in Arabidopsis, while over-expression of PfDGAT3-1 could significantly enhance the content of C18:2 and C18:3. In conclusion, in this study the characteristics and potential functions of the PfDGAT family members were elucidated. Our findings provided basic information for further functional studies and helped to increase the yield and quality of Perilla oil.

Acyl-CoA:diacylglycerol acyltransferase: Properties, physiological roles, metabolic engineering and intentional control

Acyl-CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the last reaction in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG). DGAT activity resides mainly in membrane-bound DGAT1 and DGAT2 in eukaryotes and bifunctional wax ester synthase-diacylglycerol acyltransferase (WSD) in bacteria, which are all membrane-bound proteins but exhibit no sequence homology to each other. Recent studies also identified other DGAT enzymes such as the soluble DGAT3 and diacylglycerol acetyltransferase (EaDAcT), as well as enzymes with DGAT activities including defective in cuticular ridges (DCR) and steryl and phytyl ester synthases (PESs). This review comprehensively discusses research advances on DGATs in prokaryotes and eukaryotes with a focus on their biochemical properties, physiological roles, and biotechnological and therapeutic applications. The review begins with a discussion of DGAT assay methods, followed by a systematic discussion of TAG biosynthesis and the properties and physiological role of DGATs. Thereafter, the review discusses the three-dimensional structure and insights into mechanism of action of human DGAT1, and the modeled DGAT1 from Brassica napus. The review then examines metabolic engineering strategies involving manipulation of DGAT, followed by a discussion of its therapeutic applications. DGAT in relation to improvement of livestock traits is also discussed along with DGATs in various other eukaryotic organisms.