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Transcriptome analysis reveals unique C4-like photosynthesis and oil body formation in an arachidonic acid-rich microalga Myrmecia incisa Reisigl H4301.

Ouyang LL, Chen SH, Li Y, Zhou ZG - BMC Genomics (2013)

Bottom Line: The biosynthesis pathways of lipid particularly those of ArA and triacylglycerol (TAG) were analyzed in detail, and TAG was proposed to be accumulated in oil bodies in the cytosol with the help of caleosin or oil globule-associated proteins.This transcriptomic analysis of M. incisa enabled a global understanding of mechanisms involved in photosynthesis, de novo biosynthesis of ArA, metabolism of carotenoids, and accumulation of TAG in M. incisa.These findings provided a molecular basis for the research and possibly economic exploitation of this ArA-rich microalga.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Aqua-life Sciences and Technology, Shanghai Ocean University, 999 Hucheng Huan Road, Pudong New District, Shanghai 201306, China.

ABSTRACT

Background: Arachidonic acid (ArA) is important for human health because it is one of the major components of mammalian brain membrane phospholipids. The interest in ArA inspired the search for a new sustainable source, and the green microalga Myrmecia incisa Reisigl H4301 has been found a potential ArA-producer due to a high content of intracellular ArA. To gain more molecular information about metabolism pathways, including the biosynthesis of ArA in the non-model microalga, a transcriptomic analysis was performed.

Results: The 454 pyrosequencing generated 371,740 high-quality reads, which were assembled into 51,908 unique sequences consisting of 22,749 contigs and 29,159 singletons. A total of 11,873 unique sequences were annotated through BLAST analysis, and 3,733 were assigned to Gene Ontology (GO) categories. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis uncovered a C4-like photosynthesis pathway in M. incisa. The biosynthesis pathways of lipid particularly those of ArA and triacylglycerol (TAG) were analyzed in detail, and TAG was proposed to be accumulated in oil bodies in the cytosol with the help of caleosin or oil globule-associated proteins. In addition, the carotenoid biosynthesis pathways are discussed.

Conclusion: This transcriptomic analysis of M. incisa enabled a global understanding of mechanisms involved in photosynthesis, de novo biosynthesis of ArA, metabolism of carotenoids, and accumulation of TAG in M. incisa. These findings provided a molecular basis for the research and possibly economic exploitation of this ArA-rich microalga.

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Model of the carbon concentration mechanisms in M. incisa H4301 based on the transcriptome. The dashed line indicates the routes that was not represented in this transcriptome. Abbreviations are listed as follows: PEP, phosphoenolpyruvate; AAT, aspartate aminotransferase; OAA, oxaloacetic acid; Asp, aspartate; Pi, inorganic phosphate; CA, carbonic anhydrase; MDH-NADP+, NADP-dependant malate dehydrogenase; MDH-NAD+, NAD-dependant malate dehydrogenase; ME-NADP+, NADP-dependant malic enzyme; ME-NAD+, NAD-dependant malic enzyme; PEPC, phosphoenolpyruvate carboxylase; PPCK, phosphoenolpyruvate carboxykinase; PK, pyruvate kinase; PPDK, pyruvate-phosphate dikinase; AAT, aspartate aminotransferase.
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Figure 4: Model of the carbon concentration mechanisms in M. incisa H4301 based on the transcriptome. The dashed line indicates the routes that was not represented in this transcriptome. Abbreviations are listed as follows: PEP, phosphoenolpyruvate; AAT, aspartate aminotransferase; OAA, oxaloacetic acid; Asp, aspartate; Pi, inorganic phosphate; CA, carbonic anhydrase; MDH-NADP+, NADP-dependant malate dehydrogenase; MDH-NAD+, NAD-dependant malate dehydrogenase; ME-NADP+, NADP-dependant malic enzyme; ME-NAD+, NAD-dependant malic enzyme; PEPC, phosphoenolpyruvate carboxylase; PPCK, phosphoenolpyruvate carboxykinase; PK, pyruvate kinase; PPDK, pyruvate-phosphate dikinase; AAT, aspartate aminotransferase.

Mentions: On the other hand, OAA is assumed to be reduced to malate by NAPD-dependent MDH (MDH-NADP+, EC 1.1.1.82), which targets chloroplasts [45]. Although the mechanism of the OAA shuttle from the cytosol to chloroplast is unknown [39], a unique sequence encoding chloroplast-localized MDH-NADP+ was identified in M. incisa. In addition, a putative NADP-dependent ME-coding unique sequence (ME-NADP+, EC 1.1.1.40) with 52% identity with a chloroplastic isoform [GenBank: XP_003546557] from Glycine max was annotated (Additional file 2). Dehydrogenated malate from OAA is decarboxylated by ME-NADP+ to generate two different products CO2 and pyruvate. The former product is fixed by RubisCO along with the Calvin cycle, and the latter is converted by PPDK to PEP, which is then transported to the cytosol as the substrate of PEPC by PEP/Pi translocators. There are two putative chloroplast-localized PEP/Pi translocators, and they have 74 and 52% identity with the chloroplastic isoforms from Brachypodium distachyon [GenBank: XP_003577954] and Coccomyxa subellipsoidea C-169 [GenBank: EIE22024] (Additional file 2), respectively. In addition, a unique sequence encoding a PEP/Pi antiporter was identified, demonstrating that there must be a PEP and Pi exchange between chloroplast and the cytosol in M. incisa (FigureĀ 4). The predicted subcellular localization of PPDK, which had 96% homology with that from Methylobacterium radiotolerans JCM 2831 [GenBank: YP_001755475], is unknown due to an incomplete sequence. However, the identified PEP/Pi translocator (antiporter) implied that there should be one chloroplastic PPDK in M. incisa.


Transcriptome analysis reveals unique C4-like photosynthesis and oil body formation in an arachidonic acid-rich microalga Myrmecia incisa Reisigl H4301.

Ouyang LL, Chen SH, Li Y, Zhou ZG - BMC Genomics (2013)

Model of the carbon concentration mechanisms in M. incisa H4301 based on the transcriptome. The dashed line indicates the routes that was not represented in this transcriptome. Abbreviations are listed as follows: PEP, phosphoenolpyruvate; AAT, aspartate aminotransferase; OAA, oxaloacetic acid; Asp, aspartate; Pi, inorganic phosphate; CA, carbonic anhydrase; MDH-NADP+, NADP-dependant malate dehydrogenase; MDH-NAD+, NAD-dependant malate dehydrogenase; ME-NADP+, NADP-dependant malic enzyme; ME-NAD+, NAD-dependant malic enzyme; PEPC, phosphoenolpyruvate carboxylase; PPCK, phosphoenolpyruvate carboxykinase; PK, pyruvate kinase; PPDK, pyruvate-phosphate dikinase; AAT, aspartate aminotransferase.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3686703&req=5

Figure 4: Model of the carbon concentration mechanisms in M. incisa H4301 based on the transcriptome. The dashed line indicates the routes that was not represented in this transcriptome. Abbreviations are listed as follows: PEP, phosphoenolpyruvate; AAT, aspartate aminotransferase; OAA, oxaloacetic acid; Asp, aspartate; Pi, inorganic phosphate; CA, carbonic anhydrase; MDH-NADP+, NADP-dependant malate dehydrogenase; MDH-NAD+, NAD-dependant malate dehydrogenase; ME-NADP+, NADP-dependant malic enzyme; ME-NAD+, NAD-dependant malic enzyme; PEPC, phosphoenolpyruvate carboxylase; PPCK, phosphoenolpyruvate carboxykinase; PK, pyruvate kinase; PPDK, pyruvate-phosphate dikinase; AAT, aspartate aminotransferase.
Mentions: On the other hand, OAA is assumed to be reduced to malate by NAPD-dependent MDH (MDH-NADP+, EC 1.1.1.82), which targets chloroplasts [45]. Although the mechanism of the OAA shuttle from the cytosol to chloroplast is unknown [39], a unique sequence encoding chloroplast-localized MDH-NADP+ was identified in M. incisa. In addition, a putative NADP-dependent ME-coding unique sequence (ME-NADP+, EC 1.1.1.40) with 52% identity with a chloroplastic isoform [GenBank: XP_003546557] from Glycine max was annotated (Additional file 2). Dehydrogenated malate from OAA is decarboxylated by ME-NADP+ to generate two different products CO2 and pyruvate. The former product is fixed by RubisCO along with the Calvin cycle, and the latter is converted by PPDK to PEP, which is then transported to the cytosol as the substrate of PEPC by PEP/Pi translocators. There are two putative chloroplast-localized PEP/Pi translocators, and they have 74 and 52% identity with the chloroplastic isoforms from Brachypodium distachyon [GenBank: XP_003577954] and Coccomyxa subellipsoidea C-169 [GenBank: EIE22024] (Additional file 2), respectively. In addition, a unique sequence encoding a PEP/Pi antiporter was identified, demonstrating that there must be a PEP and Pi exchange between chloroplast and the cytosol in M. incisa (FigureĀ 4). The predicted subcellular localization of PPDK, which had 96% homology with that from Methylobacterium radiotolerans JCM 2831 [GenBank: YP_001755475], is unknown due to an incomplete sequence. However, the identified PEP/Pi translocator (antiporter) implied that there should be one chloroplastic PPDK in M. incisa.

Bottom Line: The biosynthesis pathways of lipid particularly those of ArA and triacylglycerol (TAG) were analyzed in detail, and TAG was proposed to be accumulated in oil bodies in the cytosol with the help of caleosin or oil globule-associated proteins.This transcriptomic analysis of M. incisa enabled a global understanding of mechanisms involved in photosynthesis, de novo biosynthesis of ArA, metabolism of carotenoids, and accumulation of TAG in M. incisa.These findings provided a molecular basis for the research and possibly economic exploitation of this ArA-rich microalga.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Aqua-life Sciences and Technology, Shanghai Ocean University, 999 Hucheng Huan Road, Pudong New District, Shanghai 201306, China.

ABSTRACT

Background: Arachidonic acid (ArA) is important for human health because it is one of the major components of mammalian brain membrane phospholipids. The interest in ArA inspired the search for a new sustainable source, and the green microalga Myrmecia incisa Reisigl H4301 has been found a potential ArA-producer due to a high content of intracellular ArA. To gain more molecular information about metabolism pathways, including the biosynthesis of ArA in the non-model microalga, a transcriptomic analysis was performed.

Results: The 454 pyrosequencing generated 371,740 high-quality reads, which were assembled into 51,908 unique sequences consisting of 22,749 contigs and 29,159 singletons. A total of 11,873 unique sequences were annotated through BLAST analysis, and 3,733 were assigned to Gene Ontology (GO) categories. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis uncovered a C4-like photosynthesis pathway in M. incisa. The biosynthesis pathways of lipid particularly those of ArA and triacylglycerol (TAG) were analyzed in detail, and TAG was proposed to be accumulated in oil bodies in the cytosol with the help of caleosin or oil globule-associated proteins. In addition, the carotenoid biosynthesis pathways are discussed.

Conclusion: This transcriptomic analysis of M. incisa enabled a global understanding of mechanisms involved in photosynthesis, de novo biosynthesis of ArA, metabolism of carotenoids, and accumulation of TAG in M. incisa. These findings provided a molecular basis for the research and possibly economic exploitation of this ArA-rich microalga.

Show MeSH
Related in: MedlinePlus