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      Expanding the docosahexaenoic acid food web for sustainable production: engineering lower plant pathways into higher plants

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      AoB Plants
      Oxford University Press

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          Abstract

          This article describes current progress in the engineering of oilseed crops for the production of long-chain omega-3 fatty acids such as DHA. This example highlights the importance of algal genetic resources to the future of agricultural biotechnology.

          Abstract

          Background

          Algae are becoming an increasingly important component of land plant metabolic engineering projects. Land plants and algae have similar enough genetics to allow relatively straightforward gene transfer and they also share enough metabolic similarities that algal enzymes often function in a plant cell environment. Understanding metabolic systems in algae can provide insights into homologous systems in land plants. As examples, algal models are currently being used by several groups to better understand starch and lipid metabolism and catabolism, fields which have relevance in land plants. Importantly, land plants and algae also have enough metabolic divergence that algal genes can often provide new metabolic traits to plants. Furthermore, many algal genomes have now been sequenced, with many more in progress, and this easy access to genome-wide information has revealed that algal genomes are often relatively simple when compared with plants.

          Scope

          One example of the importance of algal, and in particular microalgal, resources to land plant research is the metabolic engineering of long-chain polyunsaturated fatty acids into oilseed crops which typically uses microalgal genes to extend existing natural plant biosynthetic pathways. This review describes both recent progress and remaining challenges in this field.

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          Most cited references55

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          An outlook on microalgal biofuels.

          Microalgae are considered one of the most promising feedstocks for biofuels. The productivity of these photosynthetic microorganisms in converting carbon dioxide into carbon-rich lipids, only a step or two away from biodiesel, greatly exceeds that of agricultural oleaginous crops, without competing for arable land. Worldwide, research and demonstration programs are being carried out to develop the technology needed to expand algal lipid production from a craft to a major industrial process. Although microalgae are not yet produced at large scale for bulk applications, recent advances-particularly in the methods of systems biology, genetic engineering, and biorefining-present opportunities to develop this process in a sustainable and economical way within the next 10 to 15 years.
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            Production of polyunsaturated fatty acids by polyketide synthases in both prokaryotes and eukaryotes.

            Polyunsaturated fatty acids (PUFAs) are essential membrane components in higher eukaryotes and are the precursors of many lipid-derived signaling molecules. Here, pathways for PUFA synthesis are described that do not require desaturation and elongation of saturated fatty acids. These pathways are catalyzed by polyketide synthases (PKSs) that are distinct from previously recognized PKSs in both structure and mechanism. Generation of cis double bonds probably involves position-specific isomerases; such enzymes might be useful in the production of new families of antibiotics. It is likely that PUFA synthesis in cold marine ecosystems is accomplished in part by these PKS enzymes.
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              Changes in transcript abundance in Chlamydomonas reinhardtii following nitrogen deprivation predict diversion of metabolism.

              Like many microalgae, Chlamydomonas reinhardtii forms lipid droplets rich in triacylglycerols when nutrient deprived. To begin studying the mechanisms underlying this process, nitrogen (N) deprivation was used to induce triacylglycerol accumulation and changes in developmental programs such as gametogenesis. Comparative global analysis of transcripts under induced and noninduced conditions was applied as a first approach to studying molecular changes that promote or accompany triacylglycerol accumulation in cells encountering a new nutrient environment. Towards this goal, high-throughput sequencing technology was employed to generate large numbers of expressed sequence tags of eight biologically independent libraries, four for each condition, N replete and N deprived, allowing a statistically sound comparison of expression levels under the two tested conditions. As expected, N deprivation activated a subset of control genes involved in gametogenesis while down-regulating protein biosynthesis. Genes for components of photosynthesis were also down-regulated, with the exception of the PSBS gene. N deprivation led to a marked redirection of metabolism: the primary carbon source, acetate, was no longer converted to cell building blocks by the glyoxylate cycle and gluconeogenesis but funneled directly into fatty acid biosynthesis. Additional fatty acids may be produced by membrane remodeling, a process that is suggested by the changes observed in transcript abundance of putative lipase genes. Inferences on metabolism based on transcriptional analysis are indirect, but biochemical experiments supported some of these deductions. The data provided here represent a rich source for the exploration of the mechanism of oil accumulation in microalgae.
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                Author and article information

                Journal
                AoB Plants
                aobpla
                aobpla
                AoB Plants
                Oxford University Press
                2041-2851
                2011
                18 April 2011
                2011
                : 2011
                : plr011
                Affiliations
                simpleFood Futures National Research Flagship , CSIRO Plant Industry, PO Box 1600, Canberra, ACT 2601, Australia
                Author notes
                [* ]Corresponding author's e-mail address: surinder.singh@ 123456csiro.au
                Article
                plr011
                10.1093/aobpla/plr011
                3114564
                22476481
                6a20ff34-f8d3-4e77-b12f-71e17205bb60
                Published by Oxford University Press.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 27 January 2011
                : 17 March 2011
                : 7 April 2011
                Categories
                Invited Mini-Review

                Plant science & Botany
                Plant science & Botany

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