Limits...
Oil biosynthesis in a basal angiosperm: transcriptome analysis of Persea Americana mesocarp.

Kilaru A, Cao X, Dabbs PB, Sung HJ, Rahman MM, Thrower N, Zynda G, Podicheti R, Ibarra-Laclette E, Herrera-Estrella L, Mockaitis K, Ohlrogge JB - BMC Plant Biol. (2015)

Bottom Line: The accumulation of TAG, rich in oleic acid, was associated with higher transcript levels for a putative stearoyl-ACP desaturase and endoplasmic reticulum (ER)-associated acyl-CoA synthetases, during fruit development.The orthologs that are distinctively expressed in oil-rich mesocarp tissues of this basal angiosperm, such as WRI2, ER-associated acyl-CoA synthetases, and lipid-droplet associated proteins were also identified.This study provides a foundation for future investigations to increase oil-content and has implications for metabolic engineering to enhance storage oil content in nonseed tissues of diverse species.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, East Tennessee State University, Johnson City, TN, 37614, USA. kilaru@etsu.edu.

ABSTRACT

Background: The mechanism by which plants synthesize and store high amounts of triacylglycerols (TAG) in tissues other than seeds is not well understood. The comprehension of controls for carbon partitioning and oil accumulation in nonseed tissues is essential to generate oil-rich biomass in perennial bioenergy crops. Persea americana (avocado), a basal angiosperm with unique features that are ancestral to most flowering plants, stores ~ 70 % TAG per dry weight in its mesocarp, a nonseed tissue. Transcriptome analyses of select pathways, from generation of pyruvate and leading up to TAG accumulation, in mesocarp tissues of avocado was conducted and compared with that of oil-rich monocot (oil palm) and dicot (rapeseed and castor) tissues to identify tissue- and species-specific regulation and biosynthesis of TAG in plants.

Results: RNA-Seq analyses of select lipid metabolic pathways of avocado mesocarp revealed patterns similar to that of other oil-rich species. However, only some predominant orthologs of the fatty acid biosynthetic pathway genes in this basal angiosperm were similar to those of monocots and dicots. The accumulation of TAG, rich in oleic acid, was associated with higher transcript levels for a putative stearoyl-ACP desaturase and endoplasmic reticulum (ER)-associated acyl-CoA synthetases, during fruit development. Gene expression levels for enzymes involved in terminal steps to TAG biosynthesis in the ER further indicated that both acyl-CoA-dependent and -independent mechanisms might play a role in TAG assembly, depending on the developmental stage of the fruit. Furthermore, in addition to the expression of an ortholog of WRINKLED1 (WRI1), a regulator of fatty acid biosynthesis, high transcript levels for WRI2-like and WRI3-like suggest a role for additional transcription factors in nonseed oil accumulation. Plastid pyruvate necessary for fatty acid synthesis is likely driven by the upregulation of genes involved in glycolysis and transport of its intermediates. Together, a comparative transcriptome analyses for storage oil biosynthesis in diverse plants and tissues suggested that several distinct and conserved features in this basal angiosperm species might contribute towards its rich TAG content.

Conclusions: Our work represents a comprehensive transcriptome resource for a basal angiosperm species and provides insight into their lipid metabolism in mesocarp tissues. Furthermore, comparison of the transcriptome of oil-rich mesocarp of avocado, with oil-rich seed and nonseed tissues of monocot and dicot species, revealed lipid gene orthologs that are highly conserved during evolution. The orthologs that are distinctively expressed in oil-rich mesocarp tissues of this basal angiosperm, such as WRI2, ER-associated acyl-CoA synthetases, and lipid-droplet associated proteins were also identified. This study provides a foundation for future investigations to increase oil-content and has implications for metabolic engineering to enhance storage oil content in nonseed tissues of diverse species.

No MeSH data available.


Lipid content and composition of developing fruits of avocado. a The five developing stages (I to V) of avocado fruits used for transcriptome analysis. b Fresh weight of various developing tissues with fatty acid (FA) content in mesocarp and seed. c Fatty acid composition of developing mesocarp and seed of avocado
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Fig1: Lipid content and composition of developing fruits of avocado. a The five developing stages (I to V) of avocado fruits used for transcriptome analysis. b Fresh weight of various developing tissues with fatty acid (FA) content in mesocarp and seed. c Fatty acid composition of developing mesocarp and seed of avocado

Mentions: Basal angiosperms, to which P. americana belongs, originated before the separation of monocots and dicots and contain features that are common to both groups. Transcriptome analysis of fatty acid biosynthesis in oil-rich nonseed fruit tissue has been previously reported for mesocarp of olive, a dicot [15] and oil palm, a monocot [16, 18]; similar studies of the more highly diverged basal angiosperms have not been reported. In this study, avocado mesocarp was selected for investigation of lipid biosynthesis in oil-rich tissue of an early angiosperm lineage. The mesocarp tissue from five stages of avocado fruits (I-V), with fresh weights ranging from ~ 125 to 200 g (Fig. 1a), was used to generate temporal transcriptome data, using next-generation sequencing methods (Additional file 1: Table S1). In order to associate expression patterns of lipid biosynthesis genes with temporal oil accumulation, the fatty acid content and composition of mesocarp was also analyzed (Fig. 1b and c). Details of the avocado RNA-Seq datasets available are summarized in Additional file 1: Table S1 and in NCBI BioProject PRJNA253536. Predicted functional annotation of contigs represented by at least 10 reads per kilobase per million mapped reads (RPKM) was based on BlastP alignment to lipid biosynthetic pathway proteins of Arabidopsis thaliana and is provided in Additional file 1: Table S2, along with the contig sequences (Additional file 2: Data S1). It must be noted that although transcript levels may not always reflect protein abundance or enzyme activity, similar transcriptome data has been successfully used previously to identify crucial steps in biochemical pathways [14, 16, 18]. Gene functional predictions most relevant to this study, along with their expression levels during mesocarp development are listed in Additional file 1: Table S3.Fig. 1


Oil biosynthesis in a basal angiosperm: transcriptome analysis of Persea Americana mesocarp.

Kilaru A, Cao X, Dabbs PB, Sung HJ, Rahman MM, Thrower N, Zynda G, Podicheti R, Ibarra-Laclette E, Herrera-Estrella L, Mockaitis K, Ohlrogge JB - BMC Plant Biol. (2015)

Lipid content and composition of developing fruits of avocado. a The five developing stages (I to V) of avocado fruits used for transcriptome analysis. b Fresh weight of various developing tissues with fatty acid (FA) content in mesocarp and seed. c Fatty acid composition of developing mesocarp and seed of avocado
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4537532&req=5

Fig1: Lipid content and composition of developing fruits of avocado. a The five developing stages (I to V) of avocado fruits used for transcriptome analysis. b Fresh weight of various developing tissues with fatty acid (FA) content in mesocarp and seed. c Fatty acid composition of developing mesocarp and seed of avocado
Mentions: Basal angiosperms, to which P. americana belongs, originated before the separation of monocots and dicots and contain features that are common to both groups. Transcriptome analysis of fatty acid biosynthesis in oil-rich nonseed fruit tissue has been previously reported for mesocarp of olive, a dicot [15] and oil palm, a monocot [16, 18]; similar studies of the more highly diverged basal angiosperms have not been reported. In this study, avocado mesocarp was selected for investigation of lipid biosynthesis in oil-rich tissue of an early angiosperm lineage. The mesocarp tissue from five stages of avocado fruits (I-V), with fresh weights ranging from ~ 125 to 200 g (Fig. 1a), was used to generate temporal transcriptome data, using next-generation sequencing methods (Additional file 1: Table S1). In order to associate expression patterns of lipid biosynthesis genes with temporal oil accumulation, the fatty acid content and composition of mesocarp was also analyzed (Fig. 1b and c). Details of the avocado RNA-Seq datasets available are summarized in Additional file 1: Table S1 and in NCBI BioProject PRJNA253536. Predicted functional annotation of contigs represented by at least 10 reads per kilobase per million mapped reads (RPKM) was based on BlastP alignment to lipid biosynthetic pathway proteins of Arabidopsis thaliana and is provided in Additional file 1: Table S2, along with the contig sequences (Additional file 2: Data S1). It must be noted that although transcript levels may not always reflect protein abundance or enzyme activity, similar transcriptome data has been successfully used previously to identify crucial steps in biochemical pathways [14, 16, 18]. Gene functional predictions most relevant to this study, along with their expression levels during mesocarp development are listed in Additional file 1: Table S3.Fig. 1

Bottom Line: The accumulation of TAG, rich in oleic acid, was associated with higher transcript levels for a putative stearoyl-ACP desaturase and endoplasmic reticulum (ER)-associated acyl-CoA synthetases, during fruit development.The orthologs that are distinctively expressed in oil-rich mesocarp tissues of this basal angiosperm, such as WRI2, ER-associated acyl-CoA synthetases, and lipid-droplet associated proteins were also identified.This study provides a foundation for future investigations to increase oil-content and has implications for metabolic engineering to enhance storage oil content in nonseed tissues of diverse species.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, East Tennessee State University, Johnson City, TN, 37614, USA. kilaru@etsu.edu.

ABSTRACT

Background: The mechanism by which plants synthesize and store high amounts of triacylglycerols (TAG) in tissues other than seeds is not well understood. The comprehension of controls for carbon partitioning and oil accumulation in nonseed tissues is essential to generate oil-rich biomass in perennial bioenergy crops. Persea americana (avocado), a basal angiosperm with unique features that are ancestral to most flowering plants, stores ~ 70 % TAG per dry weight in its mesocarp, a nonseed tissue. Transcriptome analyses of select pathways, from generation of pyruvate and leading up to TAG accumulation, in mesocarp tissues of avocado was conducted and compared with that of oil-rich monocot (oil palm) and dicot (rapeseed and castor) tissues to identify tissue- and species-specific regulation and biosynthesis of TAG in plants.

Results: RNA-Seq analyses of select lipid metabolic pathways of avocado mesocarp revealed patterns similar to that of other oil-rich species. However, only some predominant orthologs of the fatty acid biosynthetic pathway genes in this basal angiosperm were similar to those of monocots and dicots. The accumulation of TAG, rich in oleic acid, was associated with higher transcript levels for a putative stearoyl-ACP desaturase and endoplasmic reticulum (ER)-associated acyl-CoA synthetases, during fruit development. Gene expression levels for enzymes involved in terminal steps to TAG biosynthesis in the ER further indicated that both acyl-CoA-dependent and -independent mechanisms might play a role in TAG assembly, depending on the developmental stage of the fruit. Furthermore, in addition to the expression of an ortholog of WRINKLED1 (WRI1), a regulator of fatty acid biosynthesis, high transcript levels for WRI2-like and WRI3-like suggest a role for additional transcription factors in nonseed oil accumulation. Plastid pyruvate necessary for fatty acid synthesis is likely driven by the upregulation of genes involved in glycolysis and transport of its intermediates. Together, a comparative transcriptome analyses for storage oil biosynthesis in diverse plants and tissues suggested that several distinct and conserved features in this basal angiosperm species might contribute towards its rich TAG content.

Conclusions: Our work represents a comprehensive transcriptome resource for a basal angiosperm species and provides insight into their lipid metabolism in mesocarp tissues. Furthermore, comparison of the transcriptome of oil-rich mesocarp of avocado, with oil-rich seed and nonseed tissues of monocot and dicot species, revealed lipid gene orthologs that are highly conserved during evolution. The orthologs that are distinctively expressed in oil-rich mesocarp tissues of this basal angiosperm, such as WRI2, ER-associated acyl-CoA synthetases, and lipid-droplet associated proteins were also identified. This study provides a foundation for future investigations to increase oil-content and has implications for metabolic engineering to enhance storage oil content in nonseed tissues of diverse species.

No MeSH data available.