Analysis of Acyl Fluxes through multiple pathways of Triacylglycerol synthesis in developing Soybean embryos

Departments of Biochemistry and Molecular Biology , Michigan State University, East Lansing, Michigan 48824-1312, USA.
Plant physiology (Impact Factor: 7.39). 04/2009; 150(1):55-72. DOI: 10.1104/pp.109.137737
Source: PubMed

ABSTRACT The reactions leading to triacylglycerol (TAG) synthesis in oilseeds have been well characterized. However, quantitative analyses of acyl group and glycerol backbone fluxes that comprise extraplastidic phospholipid and TAG synthesis, including acyl editing and phosphatidylcholine-diacylglycerol interconversion, are lacking. To investigate these fluxes, we rapidly labeled developing soybean (Glycine max) embryos with [(14)C]acetate and [(14)C]glycerol. Cultured intact embryos that mimic in planta growth were used. The initial kinetics of newly synthesized acyl chain and glycerol backbone incorporation into phosphatidylcholine (PC), 1,2-sn-diacylglycerol (DAG), and TAG were analyzed along with their initial labeled molecular species and positional distributions. Almost 60% of the newly synthesized fatty acids first enter glycerolipids through PC acyl editing, largely at the sn-2 position. This flux, mostly of oleate, was over three times the flux of nascent [(14)C]fatty acids incorporated into the sn-1 and sn-2 positions of DAG through glycerol-3-phosphate acylation. Furthermore, the total flux for PC acyl editing, which includes both nascent and preexisting fatty acids, was estimated to be 1.5 to 5 times the flux of fatty acid synthesis. Thus, recycled acyl groups (16:0, 18:1, 18:2, and 18:3) in the acyl-coenzyme A pool provide most of the acyl chains for de novo glycerol-3-phosphate acylation. Our results also show kinetically distinct DAG pools. DAG used for TAG synthesis is mostly derived from PC, whereas de novo synthesized DAG is mostly used for PC synthesis. In addition, two kinetically distinct sn-3 acylations of DAG were observed, providing TAG molecular species enriched in saturated or polyunsaturated fatty acids.

Download full-text


Available from: Philip D Bates, Sep 01, 2015
  • Source
    • "DAG can also be converted to phosphatidylcholine (PtdC) via the action of phosphatidylcholine:diacylglycerol cholinephosphotransferase (PDCT) or sn-1,2-diacylglycerol:cholinephosphotransferase (CPT). It has been reported in soybean seeds that about 60% of newly synthesized acyl chains directly incorporate into the sn-2 position of PC through an acyl-editing mechanism rather than a pathway for sequential acylation of G3P [89]. PDCT has a clear seed-specific expression, but DAG-CPT does not have a clear tissue-expression–this does not immediately suggest a major role for DAG-CPT in tri-ricinolein synthesis as reported in castor [83]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Soybean (Glycine max L.) is one of the world's most important leguminous crops producing high-quality protein and oil. Increasing the relative oil concentration in soybean seeds is many researchers' goal, but a complete analysis platform of functional annotation for the genes involved in the soybean acyl-lipid pathway is still lacking. Following the success of soybean whole-genome sequencing, functional annotation has become a major challenge for the scientific community. Whole-genome transcriptome analysis is a powerful way to predict genes with biological functions. It is essential to build a comprehensive analysis platform for integrating soybean whole-genome sequencing data, the available transcriptome data and protein information. This platform could also be used to identify acyl-lipid metabolism pathways.Description: In this study, we describe our construction of the Soybean Functional Genomics Database (SFGD) using Generic Genome Browser (Gbrowse) as the core platform. We integrated microarray expression profiling with 255 samples from 14 groups' experiments and mRNA-seq data with 30 samples from four groups' experiments, including spatial and temporal transcriptome data for different soybean development stages and environmental stresses. The SFGD includes a gene co-expression regulatory network containing 23,267 genes and 1873 miRNA-target pairs, and a group of acyl-lipid pathways containing 221 enzymes and more than 1550 genes. The SFGD also provides some key analysis tools, i.e. BLAST search, expression pattern search and cis-element significance analysis, as well as gene ontology information search and single nucleotide polymorphism display. The SFGD is a comprehensive database integrating genome and transcriptome data, and also for soybean acyl-lipid metabolism pathways. It provides useful toolboxes for biologists to improve the accuracy and robustness of soybean functional genomics analysis, further improving understanding of gene regulatory networks for effective crop improvement. The SFGD is publically accessible at, with all data available for downloading.
    BMC Genomics 04/2014; 15(1):271. DOI:10.1186/1471-2164-15-271 · 4.04 Impact Factor
  • Source
    • "ies ( 34 : 1 , 34 : 2 , 36 : 2 , and 36 : 3 ) increased significantly ( by 1. 5 - to 2 . 5 - fold at 24 h ) under N - conditions ( Figure 3 ; Supplemental Data Set 3 ) , indicating the possible presence of PC - based acyl editing in membrane lipid turnover and TAG synthesis . PC acyl editing involves rapid deacylation of PC to release acyl - CoA ( Bates et al . , 2007 , 2009 ) , which is then incorporated into TAG . However , N deprivation did not cause any significant changes in most of the PE species , suggesting that these " housekeeping " lipid species may be involved in maintaining the integrity of cellular membrane structure and function ."
    [Show abstract] [Hide abstract]
    ABSTRACT: To reveal the molecular mechanisms of oleaginousness in microalgae, transcriptomic and lipidomic dynamics of the oleaginous microalga Nannochloropsis oceanica IMET1 under nitrogen-replete (N+) and N-depleted (N-) conditions were simultaneously tracked. At the transcript level, enhanced triacylglycerol (TAG) synthesis under N- conditions primarily involved upregulation of seven putative diacylglycerol acyltransferase (DGAT) genes and downregulation of six other DGAT genes, with a simultaneous elevation of the other Kennedy pathway genes. Under N- conditions, despite downregulation of most de novo fatty acid synthesis genes, the pathways that shunt carbon precursors from protein and carbohydrate metabolic pathways into glycerolipid synthesis were stimulated at the transcript level. In particular, the genes involved in supplying carbon precursors and energy for de novo fatty acid synthesis, including those encoding components of the pyruvate dehydrogenase complex (PDHC), glycolysis, and PDHC bypass, and suites of specific transporters, were substantially upregulated under N- conditions, resulting in increased overall TAG production. Moreover, genes involved in the citric acid cycle and β-oxidation in mitochondria were greatly enhanced to utilize the carbon skeletons derived from membrane lipids and proteins to produce additional TAG or its precursors. This temporal and spatial regulation model of oil accumulation in microalgae provides a basis for improving our understanding of TAG synthesis in microalgae and will also enable more rational genetic engineering of TAG production.
    The Plant Cell 04/2014; 26(4). DOI:10.1105/tpc.113.121418 · 9.58 Impact Factor
  • Source
    • "The PA is converted to 1,2-sn-diacylglycerol (DAG) [64] by the action of PA phosphatase and then DAG can be acylated to produce triacylglycerol (TAG). In developing soybean seeds, the major pathway for TAG formation is through conversion of PC to DAG and acylation of DAG to produce TAG [65]. Recently, Lee et al. [51,52] reported that the lipid profile was changed by suppression of PLDα in the soybean seeds and the total lipids and TAG signals tended to decrease in fresh seeds of PLDα-knockdown soybean. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Soybean is one of the most important oil crops. The regulatory genes involved in oil accumulation are largely unclear. We initiated studies to identify genes that regulate this process. One MYB-type gene GmMYB73 was found to display differential expression in soybean seeds of different developing stages by microarray analysis and was further investigated for its functions in lipid accumulation. GmMYB73 is a small protein with single MYB repeat and has similarity to CPC-like MYB proteins from Arabidopsis. GmMYB73 interacted with GL3 and EGL3, and then suppressed GL2, a negative regulator of oil accumulation. GmMYB73 overexpression enhanced lipid contents in both seeds and leaves of transgenic Arabidopsis plants. Seed length and thousand-seed weight were also promoted. GmMYB73 introduction into the Arabidopsis try cpc double mutant rescued the total lipids, seed size and thousand-seed weight. GmMYB73 also elevated lipid levels in seeds and leaves of transgenic Lotus, and in transgenic hairy roots of soybean plants. GmMYB73 promoted PLDalpha1 expression, whose promoter can be bound and inhibited by GL2. PLDalpha1 mutation reduced triacylglycerol levels mildly in seeds but significantly in leaves of Arabidopsis plants. GmMYB73 may reduce GL2, and then release GL2-inhibited PLDalpha1 expression for lipid accumulation. Manipulation of GmMYB73 may potentially improve oil production in legume crop plants.
    BMC Plant Biology 03/2014; 14(1):73. DOI:10.1186/1471-2229-14-73 · 3.94 Impact Factor
Show more