Transcriptomic analysis revealed the mechanism of oil dynamic accumulation during developing Siberian apricot (Prunus sibirica L.) seed kernels for the development of woody biodiesel

Specific transcription of sodium-dependent pyruvate transporter 2 increases carbon allocation into plastid glycolysis and fatty acid synthesis with high oil production in Lindera glauca seeds

BASS (Bile acid/sodium symporter) contribute greatly to pyruvate transport for oil biosynthesis. This work focused on determining critical BASS and revealing function in controlling oil biosynthesis in Lindera glauca seeds. A combination of global analysis of oil biosynthesis-related plastidial transporters and quantitative-comparison of transcription of BASS family members with oil content was conducted in L. glauca seeds across 9 differential accessions or developmental stages to determine BASS2 specific for seed oil accumulation, with BASS2-directed regulation model constructed for partitioning carbon into plastid glycolysis. BASS2 gene and its own promoter were isolated, and heterologous expression in Arabidopsis was driven respectively by the constitutive 35S and self-specific promoters. LgBASS2 overexpression, particularly controlled by native promoter, enhanced seed biomass and oil production, facilitated uptake of glycolytic metabolites into plastid, increased the amounts of plastid glycolytic metabolites and FA synthetic precursors, and upregulated transcription of key regulatory enzymes or proteins (involving sucrose cleavage, plastid transporter, glycolysis, FA biosynthesis, triacylglycerol assembly and lipid droplet budding). Our findings highlighted a significance of own promoter-controlled transcriptional expression of LgBASS2 to promoting seed development with high oil production, and provided new molecular regulation target of LgBASS2 and its own promoter to future bioengineering seed oil production.

Cytochrome P450 enzyme CYP79D16 from Prunus sibirica seeds presents a novel molecular regulatory target to bioengineering oil accumulation with less amygdalin

The seeds of Siberian apricot (Prunus sibirica L.) have abundant oils, but also contain amygdalin causing toxicity issue. This work focused on determining critical cytochrome P450 (CYP) enzyme and revealing its function in controlling amygdalin biosynthesis in P. sibirica seeds. A combination of whole-genomic identification of amygdalin synthesis-related CYPs and quantitative-comparison of transcription of CYP71/79 family members with amygdalin content in P. sibirica seeds among 18 different accessions or developmental stages was applied to identify CYP79D16 specific for seed amygdalin accumulation. The PsCYP79D16 gene was isolated, and expression and mutation were performed in yeast Saccharomyces cerevisiae, revealing high activity of PsCYP79D16 to catalyze the first step in Phe-derived amygdalin biosynthesis with ideal catalytic activity of Vmax (175.44 U/mg) and Km (0.16 mM), and functional site (Asn500). An integration of overexpression, mutation and its recovery was performed in Arabidopsis. PsCYP79D16 overexpression increased the amounts of amygdalin biosynthetic precursors and transcriptional levels of amygdalin metabolism-associated enzymes, but repressed oil accumulation and regulatory enzyme transcription (involving carbon partitioning, FA biosynthesis and triacylglycerol assembly), all of which exhibited an opposite status in cyp79d16 mutant that could be compensated by mutation restoration, unraveling a significance of PsCYP79D16 for governing seed oil and amygdalin synthesis. PsCYP79D16 should be as novel regulatory target to future bioengineering oil accumulation with less-amount amygdalin of oilseed plants.

Integrated analysis reveals functional genes and regulators associated with fatty acid biosynthesis in Elaeagnus mollis Diels

Elaeagnus mollis Diels. is a newly developed oil plant in China, which harbors high fatty acid (FA) in its kernel oil. Functional genes and regulators associated with FA biosynthesis are widely characterized in oil crops, but it still remains elusive in E. mollis. In this study, the FA and carbohydrate content, functional genes and metabolites involved in FA biosynthesis, and the potential regulator were investigated. Results demonstrated that FA and carbohydrate contents fluctuated accompanied with kernel development and reached relatively stable status at mature stage, indicating lipid and carbohydrate metabolism orchestrated for FA biosynthesis. Unsaturated FA (85.80-465.86 mg/g) occupied ∼90% of total FA (97.97-507.07 mg/g), oleic acid (OA) and linoleic acid (LA) were two major components. We identified 436 and 2735 genes involved in lipid and carbohydrate metabolism, while 178 genes directly in FA biosynthesis. Weighted gene co-expression analysis elucidated the turquoise module illustrated significant association with OA and LA content, respectively. Co-expression analysis revealed EmWRI1 was a vital regulator in E. mollis FA biosynthesis, which was proved by transgenic of EmWRI1 in Arabidopsis. Furthermore, RNA-Seq and yeast one-hybrid assay revealed the direct interaction between EmWRI1 and proEmBCCP2. This study deciphers the FA biosynthetic regulatory mechanism in E. mollis and sets a solid foundation for genetic breeding of this newly developed oil crops.

Selection of Key Genes for Apricot Kernel Oil Synthesis Based on Transcriptome Analysis

The purpose of this study was to identify the key genes regulating apricot kernel oil (AKO) biosynthesis and understand the molecular pathways of AKO synthesis and accumulation. This study used two varieties of apricot kernel to determine the oil contents and primary fatty acid compositions at different developmental stages. Candidate genes for AKO biosynthesis were selected through transcriptome sequencing technology and weighted gene co-expression network analysis (WGCNA), and these genes were verified by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The results indicate that during apricot ripening, the content of AKO exhibits an 'S'-shaped accumulation pattern. The primary fatty acid components are C18:1 and C18:2. The transcriptome sequencing produced 164.19 Gb of clean data and 17,411 differentially expressed genes. The WGCNA results indicate that significantly differentially expressed genes cluster into seven modules-gene clusters (module)-with the strongest correlations to AKO indicated in pink. Nineteen candidate genes were selected from the oil synthesis pathway and WGCNA results. The qRT-PCR results indicate that six key enzyme genes and three transcription factors play significant regulatory roles in AKO biosynthesis. This study elucidates the molecular pathways involved in AKO biosynthesis and explains the difference in oil content between bitter and sweet apricot kernels.

Regulatory mechanism of carbohydrate metabolism pathways on oil biosynthesis of oil plant Symplocos paniculata

The mechanism underlying oil synthesis in oil plant fruits remains elusive, as sugar metabolism provides the essential carbon skeleton without a clear understanding of its intricate workings. The transcriptome and oil and sugar metabolites' content of Symplocos paniculate, an extraordinary oil plant with immense ecological significance, were subjected to a comparative analysis throughout fruit development. The findings unveiled that the impact of sugar metabolism on oil synthesis varied throughout distinct stages of fruit development. Remarkably, during the initial phase of fruit development from 10 to 90 days after flowering (DAF), pivotal genes involved in starch biosynthesis, such as ADP-glucose pyrophosphorylase (AGP), starch synthase (SS), and starch branching enzyme (SBE), facilitated an earlier accumulation of starch within the fruit. Whereas, during the fruit maturation stage (from 90 DAF to 170 DAF), the expression of phosphofructokinase 1 (PFK-1), pyruvate kinase (PK) and pyruvate dehydrogenase (PDH) enzyme genes involved in the glycolysis pathway was significantly upregulated, thereby facilitating a rapid and substantial accumulation of oil. The sugar metabolism activity of S. paniculata fruit exerts a crucial influence on the process of oil synthesis, which is highly dependent on the specific developmental stage. These significant discoveries provide potential candidate genes for advanced genetic improvement using molecular biotechnology, thus enhancing both fruit oil production and modifying the composition of fatty acids.

The Evolution of Lipidomics during Oil Accumulation of Plukenetia volubilis Seeds

Sacha inchi (Plukenetia volubilis) is a valuable oilseed crop with a high content of polyunsaturated fatty acids (PUFAs). However, there is a lack of in-depth understanding of the lipidomics in Sacha inchi seeds (SIDs). Saturated fatty acids occupied more than half of the proportion (59.31%) in early development, while PUFAs accounted for 78.92% at maturation. The main triacylglycerols were TAG(18:3/18:3/18:3), TAG(18:2/18:2/18:3), and TAG(16:0/18:2/18:2). The corresponding species (18:3/18:3, 18:2/18:2, and 16:0/18:2) were also the main ingredients in diacylglycerol and phosphatidic acid, indicating high PUFA composition in the sn-1 and sn-2 positions of TAG. Only LPC(18:3), LPC(18:2), and LPC(16:0) were identified in SIDs, implying that those PUFAs on the sn-2 positions of the PC(18:3/-), PC(18:2/-), and PC(16:0/-) categories were released into the acyl-CoA pool for the Kennedy pathway. Conversely, the PC(18:1/-) and PC(18:0/-) categories might be responsible for the generation of PC-derived DAG and TAG. The lipidomics data will contribute to understanding the TAG assembly in developing SIDs, especially for PUFAs.

Mandelonitrile lyase MDL2-mediated regulation of seed amygdalin and oil accumulation of Prunus Sibirica

BACKGROUND

The Prunus sibirica seeds with rich oils has great utilization, but contain amygdalin that can be hydrolyzed to release toxic HCN. Thus, how to effectively reduce seed amygdalin content of P. sibirica is an interesting question. Mandelonitrile is known as one key intermediate of amygdalin metabolism, but which mandelonitrile lyase (MDL) family member essential for its dissociation destined to low amygdalin accumulation in P. sibirica seeds still remains enigmatic. An integration of our recent 454 RNA-seq data, amygdalin and mandelonitrile content detection, qRT-PCR analysis and function determination is described as a critical attempt to determine key MDL and to highlight its function in governing mandelonitrile catabolism with low amygdalin accumulation in Prunus sibirica seeds for better developing edible oil and biodiesel in China.

RESULTS

To identify key MDL and to unravel its function in governing seed mandelonitrile catabolism with low amygdalin accumulation in P. sibirica. Global identification of mandelonitrile catabolism-associated MDLs, integrated with the across-accessions/developing stages association of accumulative amount of amygdalin and mandelonitrile with transcriptional level of MDLs was performed on P. sibirica seeds of 5 accessions to determine crucial MDL2 for seed mandelonitrile catabolism of P. sibirica. MDL2 gene was cloned from the seeds of P. sibirica, and yeast eukaryotic expression revealed an ability of MDL2 to specifically catalyze the dissociation of mandelonitrile with the ideal values of Km (0.22 mM) and Vmax (178.57 U/mg). A combination of overexpression and mutation was conducted in Arabidopsis. Overexpression of PsMDL2 decreased seed mandelonitrile content with an increase of oil accumulation, upregulated transcript of mandelonitrile metabolic enzymes and oil synthesis enzymes (involving FA biosynthesis and TAG assembly), but exhibited an opposite situation in mdl2 mutant, revealing a role of PsMDL2-mediated regulation in seed amygdalin and oil biosynthesis. The PsMDL2 gene has shown as key molecular target for bioengineering high seed oil production with low amygdalin in oilseed plants.

CONCLUSIONS

This work presents the first integrated assay of genome-wide identification of mandelonitrile catabolism-related MDLs and the comparative association of transcriptional level of MDLs with accumulative amount of amygdalin and mandelonitrile in the seeds across different germplasms and developmental periods of P. sibirica to determine MDL2 for mandelonitrile dissociation, and an effective combination of PsMDL2 expression and mutation, oil and mandelonitrile content detection and qRT-PCR assay was performed to unravel a mechanism of PsMDL2 for controlling amygdalin and oil production in P. sibirica seeds. These findings could offer new bioengineering strategy for high oil production with low amygdalin in oil plants.

Transcriptome analysis reveals the mechanism of different fruit appearance between apricot (Armeniaca vulgaris Lam.) and its seedling

BACKGROUND

Apricot fruit has great economic value. In the process of apricot breeding using traditional breeding methods, we obtained a larger seedling (named Us) from the original variety (named U). And Us fruit is larger than U, taste better. Therefore, revealing its mechanism is very important for Apricot breeding.

METHODS

In this study, de novo assembly and transcriptome sequencing (RNA-Seq) was used to screen the differently expressed genes (DEGs) between U and Us at three development stages, including young fruits stage, mid-ripening stage and mature fruit stage.

RESULTS

The results showed that there were 6,753 DEGs at different sampling time. "Cellulose synthase (UDP-forming) activity" and "cellulose synthase activity" were the key GO terms enriched in GO, of which CESA and CSL family played a key role. "Photosynthesis-antenna proteins" and "Plant hormone signal transduction" were the candidate pathways and lhca, lhcb, Aux/IAA and SAUR were the main regulators.

CONCLUSION

The auxin signaling pathway was active in Us, of which Aux/IAAs and SAUR were the key fruit size regulators. The low level of lhca and lhcb in Us could reveal the low demand for exogenous carbon, but they increased at mature stage, which might be due to the role of aux, who was keeping the fruit growing. Aux and photosynthesis maight be the main causes of appearance formation of Us fruits. Interestingly, the higher expression of CESA and CSL proved that Us entered the hardening process earlier than U. The advanced developmental progress might also be due to the role of Aux.

Determination of superior Pistacia chinensis accession with high-quality seed oil and biodiesel production and revelation of LEC1/WRI1-mediated high oil accumulative mechanism for better developing woody biodiesel

BACKGROUND

Based on our previous studied on different provenances of Pistacia chinensis, some accessions with high quality and quantity of seed oils has emerged as novel source of biodiesel. To better develop P. chinensis seed oils as woody biodiesel, a concurrent exploration of oil content, FA profile, biodiesel yield, and fuel properties was conducted on the seeds from 5 plus germplasms to determine superior genotype for ideal biodiesel production. Another vital challenge is to unravel mechanism that govern the differences in oil content and FA profile of P. chinensis seeds across different accessions. FA biosynthesis and oil accumulation of oil plants are known to be highly controlled by the transcription factors. An integrated analysis of our recent transcriptome data, qRT-PCR detection and functional identification was performed as an attempt to highlight LEC1/WRI1-mediated transcription regulatory mechanism for high-quality oil accumulation in P. chinensis seeds.

RESULTS

To select ideal germplasm and unravel high oil accumulative mechanism for developing P. chinensis seed oils as biodiesel, five plus trees (accession PC-BJ/PC-AH/PC-SX/PC-HN/PC-HB) with high-yield seeds were selected to assess the variabilities in weight, oil content, FA profile, biodiesel yield and fuel property, revealing a variation in the levels of seed oil (50.76-60.88%), monounsaturated FA (42.80-70.72%) and polyunsaturated FA (18.78-43.35%), and biodiesel yield (84.98-98.15%) across different accessions. PC-HN had a maximum values of seed weight (26.23 mg), oil (60.88%) and biodiesel yield (98.15%), and ideal proportions of C18:1 (69.94%), C18:2 (17.65%) and C18:3 (1.13%), implying that seed oils of accession PC-HN was the most suitable for ideal biodiesel production. To highlight molecular mechanism that govern such differences in oil content and FA profile of different accessions, a combination of our recent transcriptome data, qRT-PCR detection and protein interaction analysis was performed to identify a pivotal role of LEC1/WRI1-mediated transcription regulatory network in high oil accumulation of P. chinensis seeds from different accessions. Notably, overexpression of PcWRI1 or PcLEC1 from P. chinensis seeds in Arabidopsis could facilitate seed development and upregulate several genes relevant for carbon flux allocation (plastidic glycolysis and acetyl-CoA generation), FA synthesis, TAG assembly and oil storage, causing an increase in seed oil content and monounsaturated FA level, destined for biodiesel fuel property improvement. Our findings may present strategies for better developing P. chinensis seed oils as biodiesel feedstock and bioengineering its high oil accumulation.

CONCLUSIONS

This is the first report on the cross-accessions assessments of P. chinensis seed oils to determine ideal accession for high-quality biodiesel production, and an effective combination of PcWRI1 or PcLEC1 overexpression, morphological assay, oil accumulation and qRT-PCR detection was applied to unravel a role of LEC1/WRI1-mediated regulatory network for oil accumulation in P. chinensis seeds, and to highlight the potential application of PcWRI1 or PcLEC1 for increasing oil production. Our finding may provide new strategies for developing biodiesel resource and molecular breeding.

Evaluation of oil accumulation and biodiesel property of Lindera glauca fruits among different germplasms and revelation of high oil producing mechanism for developing biodiesel

BACKGROUND

Lindera glauca with rich resource and fruit oil has emerged as novel source of biodiesel in China, but different germplasms show a variation for fruit oil content and FA profile. To develop L. glauca fruit oils as biodiesel, a concurrent exploration of oil content, FA composition, biodiesel yield, fuel property and prediction model construction was conducted on the fruits from 8 plus germplasms to select superior genotype for ideal biodiesel production. Another vital focus was to highlight mechanism that govern the differences in oil content and FA profile of different germplasms. The cross-accessions comparisons associated with oil-synthesized gene transcriptional level and oil accumulative amount led to the identification of potential determinants (enzymes, transporters or transcription factors) and regulatory mechanisms responsible for high-quality oil accumulation.

RESULTS

To select superior germplasm and unravel regulatory mechanism of high oil production for developing L. glauca fruit oils as biodiesel, 8 plus trees (accession LG01/02/03/04/05/06/07/08) with high-yield fruits were selected to evaluate the differences in oil content, FA profile, biodiesel yield and fuel property, and to construct fuel property prediction model, revealing a variation in the levels of fruit oil (45.12-60.95%), monounsaturated FA (52.43-78.46%) and polyunsaturated FA (17.69-38.73%), and biodiesel yield (80.12-98.71%) across different accessions. Of note, LG06 had a maximum yield of oil (60.95%) and biodiesel (98.71%), and ideal proportions of C18:1 (77.89%), C18:2 (14.16%) and C18:3 (1.55%), indicating that fruit oils from accession LG06 was the most suitable for high-quality biodiesel production. To highlight molecular mechanism that govern such differences in oil content and FA composition of different accessions, the quantitative relationship between oil-synthesized gene transcription and oil accumulative amount were conducted on different accessions to identify some vital determinants (enzymes, transporters or transcription factors) with a model of carbon metabolic regulatory for high-quality oil accumulation by an integrated analysis of our recent transcriptome data and qRT-PCR detection. Our findings may present strategies for developing L. glauca fruit oils as biodiesel feedstock and engineering its oil accumulation.

CONCLUSIONS

This is the first report on the cross-accessions evaluations of L. glauca fruit oils to determine ideal accession for producing ideal biodiesel, and the associations of oil accumulative amount with oil-synthesized gene transcription was performed to identify some crucial determinants (enzymes, transporters or transcription factors) with metabolic regulation model established for governing high oil production. Our finding may provide molecular basis for new strategies of developing biodiesel resource and engineering oil accumulation.

Transcriptomic Analyses Reveal Key Genes Involved in Pigment Biosynthesis Related to Leaf Color Change of Liquidambar formosana Hance

Liquidambar formosana Hance has a highly ornamental value as an important urban greening tree species with bright and beautiful leaf color. To gain insights into the physiological and molecular mechanisms of L. formosana leaf color change, the leaves of three different clones were sampled every ten days from October 13, 2019, five times in total, which are S1, S2, S3, S4 and S5. Transcriptome sequencing was performed at S1 and S4. The chlorophyll content of the three clones decreased significantly, while the anthocyanins content of the three clones increased significantly in the coloring stage. The anthocyanins content of clone 2 was far more than that of the other two clones throughout the period of leaf color change. The transcriptome analysis showed that six DEGs related to anthocyanins biosynthesis, including CHS (chalcone synthase), CHI (chalcone isomerase), F3′H (flavonoid 3′-hydroxylase), DFR (dihydroflavonol 4-reductase), ANS (anthocyanidin synthase) and FLS (flavonol synthase), were found in three clones. Clone 2 has another three DEGs related to anthocyanins biosynthesis, including PAL (Phenylalanine ammonia-lyase), F3′5′H (flavonoid 3′,5′-hydroxylase) and UFGT (flavonoid 3-O-glucosyltransferase). We lay a foundation for understanding the molecular regulation mechanism of the formation of leaf color by exploring valuable genes, which is helpful for L. formosana breeding.

Effects of Fruit Shading on Gene and Protein Expression During Starch and Oil Accumulation in Developing Styrax tonkinensis Kernels

Styrax tonkinensis has great potential as a biofuel feedstock source having industrial oilseeds with excellent fatty acids (FAs) composition and good fuel properties. Photosynthesis in the developing pericarp could affect the carbon distribution in kernel. During kernel development, more carbon sources are allocated to starch rather than lipid, when the pericarp photosynthesis is reduced by fruit shading treatment. After shading the fruits at 50 days after flowering (DAF), samples of shaded fruit (FSK) and controls (CK) were collected at 80 DAF and analyzed using the proteomic method. We identified 3,181 proteins, of which 277 were differentially expressed proteins, all downregulated in the FSK group. There were 56 proteins found involved in carbohydrate metabolism and lipid biosynthesis leading to oil accumulation with their iTRAQ ratios of FSK/CK ranging from 0.7123 to 1.1075. According to the qRT-PCR analyses, the key genes related to FA and triacylglycerol (TAG) biosynthesis were significantly downregulated between 60 and 90 DAF especially at 80 DAF, while the key genes involved in starch biosynthesis and FA desaturase had no significant difference between the two groups at 80 DAF. Fruit shading is a negative treatment for lipid accumulation but not starch accumulation by restraining enzymic protein expression involved in FA and TAG biosynthesis during S. tonkinensis kernel development.

Proteomic analysis of metabolic mechanisms associated with fatty acid biosynthesis during Styrax tonkinensis kernel development

BACKGROUND

Styrax tonkinensis is a white-flowered tree with considerable potential as a feedstock source for biodiesel production from the oily seed contained within its nutlike drupes. Transcriptome changes during oil accumulation have been previously reported, but not concurrent changes in the proteome.

RESULTS

Using proteomic analysis of samples collected at 50, 70, 100 and 130 days after flowering (DAF), we identified 1472 differentially expressed proteins (DEPs). Based on their expression patterns, we grouped the DEPs into nine clusters and analyzed the pathway enrichment. Proteins related to starch and sucrose metabolism were most abundant at 50 DAF. Proteins involved in fatty acid (FA) biosynthesis were mainly grouped into a cluster that peaked at 70 DAF. Proteins related to protein processing in endoplasmic reticulum had two major patterns, trending either upwards or downwards, while proteins involved in amino acid biosynthesis showed more complex relationships. We identified 42 key enzymes involved in lipid accumulation during kernel development, including the acetyl-CoA carboxylase complex (ACC) and the pyruvate dehydrogenase complex (PDC). One oil body membrane protein, oleosin, continuously increased during kernel development.

CONCLUSION

A regulatory network of oil accumulation processes was built based on protein and available transcriptome expression data, which were in good temporal agreement. This analysis placed ACC and PDC in the center of the network, suggesting that the glycolytic provision of substrate plays a central regulatory role in FA biosynthesis and oil accumulation. © 2021 Society of Chemical Industry.

Transcriptomic Analysis Reveals Key Genes Involved in Oil and Linoleic Acid Biosynthesis during Artemisia sphaerocephala Seed Development

Artemisia sphaerocephala seeds are rich in polysaccharides and linoleic acid (C18:2), which have been widely used as traditional medicine and to improve food quality. The accumulation patterns and molecular regulatory mechanisms of polysaccharides during A. sphaerocephala seed development have been studied. However, the related research on seed oil and C18:2 remain unclear. For this study, A. sphaerocephala seeds at seven different development stages at 10, 20, 30, 40, 50, 60, and 70 days after flowering (designated as S1~S7), respectively, were employed as experimental samples, the accumulation patterns of oil and fatty acids (FA) and the underlying molecular regulatory mechanisms were analyzed. The results revealed that oil content increased from 10.1% to 20.0% in the early stages of seed development (S1~S2), and up to 32.0% in mature seeds, of which C18:2 accounted for 80.6% of the total FA. FA and triacylglycerol biosynthesis-related genes jointly involved in the rapid accumulation of oil in S1~S2. Weighted gene co-expression network analysis showed that transcription factors FUS3 and bHLH played a critical role in the seed oil biosynthesis. The perfect harmonization of the high expression of FAD2 with the extremely low expression of FAD3 regulated the accumulation of C18:2. This study uncovered the gene involved in oil biosynthesis and molecular regulatory mechanisms of high C18:2 accumulation in A. sphaerocephala seeds; thus, advancing research into unsaturated fatty acid metabolism in plants while generating valuable genetic resources for optimal C18:2 breeding.

Transcriptomic analysis of α-linolenic acid content and biosynthesis in Paeonia ostii fruits and seeds

BACKGROUND

Paeonia ostii is a potentially important oilseed crop because its seed yield is high, and the seeds are rich in α-linolenic acid (ALA). However, the molecular mechanisms underlying ALA biosynthesis during seed kernel, seed testa, and fruit pericarp development in this plant are unclear. We used transcriptome data to address this knowledge gap.

RESULTS

Gas chromatograph-mass spectrometry indicated that ALA content was highest in the kernel, moderate in the testa, and lowest in the pericarp. Therefore, we used RNA-sequencing to compare ALA synthesis among these three tissues. We identified 227,837 unigenes, with an average length of 755 bp. Of these, 1371 unigenes were associated with lipid metabolism. The fatty acid (FA) biosynthesis and metabolism pathways were significantly enriched during the early stages of oil accumulation in the kernel. ALA biosynthesis was significantly enriched in parallel with increasing ALA content in the testa, but these metabolic pathways were not significantly enriched during pericarp development. By comparing unigene transcription profiles with patterns of ALA accumulation, specific unigenes encoding crucial enzymes and transcription factors (TFs) involved in de novo FA biosynthesis and oil accumulation were identified. Specifically, the bell-shaped expression patterns of genes encoding SAD, FAD2, FAD3, PDCT, PDAT, OLE, CLE, and SLE in the kernel were similar to the patterns of ALA accumulation in this tissue. Genes encoding BCCP, BC, KAS I- III, and FATA were also upregulated during the early stages of oil accumulation in the kernel. In the testa, the upregulation of the genes encoding SAD, FAD2, and FAD3 was followed by a sharp increase in the concentrations of ALA. In contrast, these genes were minimally expressed (and ALA content was low) throughout pericarp development.

CONCLUSIONS

We used three tissues with high, moderate, and low ALA concentrations as an exemplar system in which to investigate tissue-specific ALA accumulation mechanisms in P. ostii. The genes and TFs identified herein might be useful targets for future studies of ALA accumulation in the tree peony. This study also provides a framework for future studies of FA biosynthesis in other oilseed plants.

Transcriptome analysis of genes involved in starch biosynthesis in developing Chinese chestnut (Castanea mollissima Blume) seed kernels

Chinese chestnut (Castanea mollissima Blume) seed kernels (CCSK) with high quality and quantity of starch has emerged as a potential raw material for food industry, but the molecular regulatory mechanism of starch accumulation in developing CCSK is still unclear. In this study, we firstly analyzed the fruit development, starch accumulation, and microscopic observation of dynamic accumulation of starch granules of developing CCSK from 10 days after flowering (DAF) to 100 DAF, of which six representative CCSK samples (50–100 DAF) were selected for transcriptome sequencing analysis. Approximately 40 million valid reads were obtained, with an average length of 124.95 bp, which were searched against a reference genome, returning 38,146 unigenes (mean size = 1164.19 bp). Using the DESeq method, 1968, 1573, 1187, 1274, and 1494 differentially expressed unigenes were identified at 60:50, 70:60, 80:70, 90:80 and 100:90 DAF, respectively. The relationship between the unigene transcriptional profiles and starch dynamic patterns in developing CCSK was comparatively analyzed, and the specific unigenes encoding for metabolic enzymes (SUSY2, PGM, PGI, GPT, NTT, AGP3, AGP2, GBSS1, SS1, SBE1, SBE2.1, SBE2.2, ISA1, ISA2, ISA3, and PHO) were characterized to be involved potentially in the biosynthesis of G-1-P, ADPG, and starch. Finally, the temporal transcript profiles of genes encoding key enzymes (susy2, pgi2, gpt1, agp2, agp3, gbss1, ss1, sbe1, sbe2.1, sbe2.2, isa1, isa2, isa3, and pho) were validated by quantitative real-time PCR (qRT-PCR). Our findings could help to reveal the molecular regulatory mechanism of starch accumulation in developing CCSK and may also provide potential candidate genes for increasing starch content in Chinese chestnut or other starchy crops.

Effects of exogenous abscisic acid on oil content, fatty acid composition, biodiesel properties and lipid components in developing Siberian apricot (Prunus sibirica) seeds

Previous studies in Siberian apricot (Prunus sibirica) seed kernel (SASK) have suggested the involvement of abscisic acid (ABA) signaling pathway in oil accumulation. However, there are few reports on the effects of ABA on the metabolism of fatty acids (FA) in seed development. Here, we first evaluated the response of developing SASK to ABA treatment, with a focus on oil content, FA composition, biodiesel properties, lipid compounds and gene expressions. Compared with control samples, the application of exogenous ABA increased the total oil content by 6.55% in mature SASK. The C18:1 content markedly increased in ABA treatment, and conversely C16:0 decreased. Exogenous ABA also improved the biodiesel properties of SASK oil, making it better suited to the specifications of biodiesel standards. Furthermore, the molecular species of phosphatidylcholine (PC), phosphatidic acid (PA), diacylglycerol (DAG) and triacylglycerol (TAG) were detected using lipidomics analysis. The 18:1/18:1 was the main component in PA, PC and DAG, while the main components of 18:1/18:1/18:2, 18:1/18:1/18:3, 18:2/18:2/18:2 and 18:1/18:1/18:1 in TAG. Most lipid species gradually increased with SASK maturity. In addition, the relative contents of TAG-18:1/18:1/18:2 and TAG-18:1/18:1/18:1 in developing SASK increased with the application of exogenous ABA. We also detected elevated gene expression of key genes involved in ABA chemical pathway, which likely affected FA biosynthesis and accumulation. Our results provide insight into the effects of ABA on the oil accumulation in developing SASK, which has direct applications to improving the quality of SASK-derived biodiesel.

Comparative transcriptome analyses define genes and gene modules differing between two Populus genotypes with contrasting stem growth rates

BACKGROUND

Wood provides an important biomass resource for biofuel production around the world. The radial growth of tree stems is central to biomass production for forestry and biofuels, but it is challenging to dissect genetically because it is a complex trait influenced by many genes. In this study, we adopted methods of physiology, transcriptomics and genetics to investigate the regulatory mechanisms of tree radial growth and wood development.

RESULTS

Physiological comparison showed that two Populus genotypes presented different rates of radial growth of stems and accumulation of woody biomass. A comparative transcriptional network approach was used to define and characterize functional differences between two Populus genotypes. Analyses of transcript profiles from wood-forming tissue of the two genotypes showed that 1542, 2295 and 2110 genes were differentially expressed in the pre-growth, fast-growth and post-growth stages, respectively. The co-expression analyses identified modules of co-expressed genes that displayed distinct expression profiles. Modules were further characterized by correlating transcript levels with genotypes and physiological traits. The results showed enrichment of genes that participated in cell cycle and division, whose expression change was consistent with the variation of radial growth rates. Genes related to secondary vascular development were up-regulated in the faster-growing genotype in the pre-growth stage. We characterized a BEL1-like (BELL) transcription factor, PeuBELL15, which was up-regulated in the faster-growing genotype. Analyses of transgenic Populus overexpressing as well as CRISPR/Cas9-induced mutants for BELL15 showed that PeuBELL15 improved accumulation of glucan and lignin, and it promoted secondary vascular growth by regulating the expression of genes relevant for cellulose synthases and lignin biosynthesis.

CONCLUSIONS

This study illustrated that active division and expansion of vascular cambium cells and secondary cell wall deposition of xylem cells contribute to stem radial increment and biomass accumulation, and it identified relevant genes for these complex growth traits, including a BELL transcription factor gene PeuBELL15. This provides genetic resources for improving and breeding elite genotypes with fast growth and high wood biomass.

Transcriptome analysis of metabolic pathways associated with oil accumulation in developing seed kernels of Styrax tonkinensis, a woody biodiesel species

BACKGROUND

Styrax tonkinensis (Pierre) Craib ex Hartwich has great potential as a woody biodiesel species having seed kernels with high oil content, excellent fatty acid composition and good fuel properties. However, no transcriptome information is available on the molecular regulatory mechanism of oil accumulation in developing S. tonkinensis kernels.

RESULTS

The dynamic patterns of oil content and fatty acid composition at 11 time points from 50 to 150 days after flowering (DAF) were analyzed. The percent oil content showed an up-down-up pattern, with yield and degree of unsaturation peaking on or after 140 DAF. Four time points (50, 70, 100, and 130 DAF) were selected for Illumina transcriptome sequencing. Approximately 73 million high quality clean reads were generated, and then assembled into 168,207 unigenes with a mean length of 854 bp. There were 5916 genes that were differentially expressed between different time points. These differentially expressed genes were grouped into 9 clusters based on their expression patterns. Expression patterns of a subset of 12 unigenes were confirmed by qRT-PCR. Based on their functional annotation through the Basic Local Alignment Search Tool and publicly available protein databases, specific unigenes encoding key enzymes, transmembrane transporters, and transcription factors associated with oil accumulation were determined. Three main patterns of expression were evident. Most unigenes peaked at 70 DAF, coincident with a rapid increase in oil content during kernel development. Unigenes with high expression at 50 DAF were associated with plastid formation and earlier stages of oil synthesis, including pyruvate and acetyl-CoA formation. Unigenes associated with triacylglycerol biosynthesis and oil body development peaked at 100 or 130 DAF.

CONCLUSIONS

Transcriptome changes during oil accumulation show a distinct temporal trend with few abrupt transitions. Expression profiles suggest that acetyl-CoA formation for oil biosynthesis is both directly from pyruvate and indirectly via acetaldehyde, and indicate that the main carbon source for fatty acid biosynthesis is triosephosphate originating from phosphohexose outside the plastid. Different sn-glycerol-3-phosphate acyltransferases are implicated in diacylglycerol biosynthesis at early versus late stages of oil accumulation. Triacylglycerol biosynthesis may be accomplished by both diacylglycerol and by phospholipid:diacylglycerol acyltransferases.

WRINKLED1 transcription factor orchestrates the regulation of carbon partitioning for C18:1 (oleic acid) accumulation in Siberian apricot kernel

WRINKLED1 (WRI1), an APETALA2 (AP2)-type transcription factor, has been shown to be required for the regulation of carbon partitioning into fatty acid (FA) synthesis in plant seeds. To our knowledge, the regulatory network of WRI1 remains unknown in Prunus sibirica kernel (PSK), a novel woody biodiesel feedstock in China. In this study, based on the transcriptional data from developing oilseeds of multiple plant species, we identified 161 WRI1-coexpressed genes using weighted gene co-expression network analysis (WGCNA). The major portion of WRI1-coexpressed genes was characterized to be involved in carbon partitioning and FA biosynthesis. Additionally, we detected the temporal patterns for oil content and FA compositions in developing PSK from two different germplasms (AS-85 and AS-86). The major differences between the two germplasms are higher contents of oil and C18:1 in AS-85 than in AS-86 at a mature stage. Thus, AS-85 and AS-86 are desirable materials to explore the molecular and metabolic mechanisms of oil accumulation in Siberian apricot. Expression analysis in developing PSK of AS-85 and AS-86 indicated that the expression level of P. sibirica WRI1 (PsWRI1) was closely correlated to accumulative rate of oil. Also, the comparison of expression profiles in developing PSK of AS-85 and AS-86 displayed that the pPK, E1-α, E2, TAL, BC, MCMT, BS, SAD and FAD2 have a high correlation with PsWRI1. Transient expression showed that Pro_SAD- and Pro_BS-driving GUS expression showed no substantial difference between AS-85 and AS-86, while the expression level of Pro_PEPCK-AS-85 driving GUS was significantly higher than that of Pro_PEPCK-AS-86 driving GUS. Additionally, transient co-transformation with PsWRI1 revealed that Pro_SAD, Pro_PEPCK and Pro_BS activity could be specifically up-regulated by PsWRI1. This regulatory mechanism of PsWRI1 may create a steep concentration difference, thereby facilitating carbon flux into C18:1 accumulation in developing PSK. Overall, all our findings imply a versatile mechanism of WRI1 to optimize carbon allocation for oil accumulation, which can provide reference for researching the woody biodiesel plants.

Transcriptional regulatory networks controlling taste and aroma quality of apricot (Prunus armeniaca L.) fruit during ripening

BACKGROUND

Taste and aroma, which are important organoleptic qualities of apricot (Prunus armeniaca L.) fruit, undergo rapid and substantial changes during ripening. However, the associated molecular mechanisms remain unclear. The goal of this study was to identify candidate genes for flavor compound metabolism and to construct a regulatory transcriptional network.

RESULTS

We characterized the transcriptome of the 'Jianali' apricot cultivar, which exhibits substantial changes in flavor during ripening, at 50 (turning), 73 (commercial maturation) and 91 (full ripe) days post anthesis (DPA) using RNA sequencing (RNA-Seq). A weighted gene co-expression network analysis (WGCNA) revealed that four of 19 modules correlated highly with flavor compound metabolism (P < 0.001). From them, we identified 1237 differentially expressed genes, with 16 intramodular hubs. A proposed pathway model for flavor compound biosynthesis is presented based on these genes. Two SUS1 genes, as well as SPS2 and INV1 were correlated with sugar biosynthesis, while NADP-ME4, two PK-like and mitochondrial energy metabolism exerted a noticeable effect on organic acid metabolism. CCD1 and FAD2 were identified as being involved in apocarotenoid aroma volatiles and lactone biosynthesis, respectively. Five sugar transporters (Sweet10, STP13, EDR6, STP5.1, STP5.2), one aluminum-activated malate transporter (ALMT9) and one ABCG transporter (ABCG11) were associated with the transport of sugars, organic acids and volatiles, respectively. Sixteen transcription factors were also highlighted that may also play regulatory roles in flavor quality development.

CONCLUSIONS

Apricot RNA-Seq data were obtained and used to generate an annotated set of predicted expressed genes, providing a platform for functional genomic research. Using network analysis and pathway mapping, putative molecular mechanisms for changes in apricot fruit taste and aroma during ripening were elucidated.

Comprehensive evaluation of fuel properties and complex regulation of intracellular transporters for high oil production in developing seeds of Prunus sibirica for woody biodiesel

BACKGROUND

Based on our previous studies of 17 Prunus sibirica germplasms, one plus tree with high quality and quantity of seed oils has emerged as novel potential source of biodiesel. To better develop P. sibirica seed oils as woody biodiesel, a concurrent exploration of oil content, FA composition, biodiesel yield and fuel properties as well as prediction model construction for fuel properties was conducted on developing seeds to determine the optimal seed harvest time for producing high-quality biodiesel. Oil synthesis required supply of carbon source, energy and FA, but their transport mechanisms still remains enigmatic. Our recent 454 sequencing of P. sibirica could provide long-read sequences to identify membrane transporters for a better understanding of regulatory mechanism for high oil production in developing seeds.

RESULTS

To better develop the seed oils of P. sibirica as woody biodiesel, we firstly focused on a temporal and comparative evaluation of growth tendency, oil content, FA composition, biodiesel yield and fuel properties as well as model construction for biodiesel property prediction in different developing seeds from P. sibirica plus tree (accession AS-80), revealing that the oils from developing seeds harvested after 60 days after flowering (DAF) could be as novel potential feedstock for producing biodiesel with ideal fuel property. To gain new insight into membrane transport mechanism for high oil yield in developing seeds of P. sibirica, we presented a global analysis of transporter based on our recent 454 sequencing data of P. sibirica. We annotated a total of 116 genes for membrane-localized transporters at different organelles (plastid, endoplasmatic reticulum, tonoplast, mitochondria and peroxisome), of which some specific transporters were identified to be involved in carbon allocation, metabolite transport and energy supply for oil synthesis by both RT-PCR and qRT-PCR. Importantly, the transporter-mediated model was well established for high oil synthesis in developing P. sibirica seeds. Our findings could help to reveal molecular mechanism of increased oil production and may also present strategies for engineering oil accumulation in oilseed plants.

CONCLUSIONS

This study presents a temporal and comparative evaluation of developing P. sibirica seed oils as a potential feedstock for producing high-quality biodiesel and a global identification for membrane transporters was to gain better insights into regulatory mechanism of high oil production in developing seeds of P. sibirica. Our findings may present strategies for developing woody biodiesel resources and engineering oil accumulation.

Identification of AUXIN RESPONSE FACTOR gene family from Prunus sibirica and its expression analysis during mesocarp and kernel development

BACKGROUND

Auxin response factors (ARFs) in auxin signaling pathway are an important component that can regulate the transcription of auxin-responsive genes involved in almost all aspects of plant growth and development. To our knowledge, the comprehensive and systematic characterization of ARF genes has never been reported in Prunus sibirica, a novel woody biodiesel feedstock in China.

RESULTS

In this study, we identified 14 PsARF genes with a perfect open reading frame (ORF) in P. sibirica by using its previous transcriptomic data. Conserved motif analysis showed that all identified PsARF proteins had typical DNA-binding and ARF domain, but 5 members (PsARF3, 8 10, 16 and 17) lacked the dimerization domain. Phylogenetic analysis of the ARF proteins generated from various plant species indicated that ARFs could be categorized into 4 major groups (Class I, II, III and IV), in which all identified ARFs from P. sibirica showed a closest relationship with those from P. mume. Comparison of the expression profiles of 14 PsARF genes in different developmental stages of Siberian apricot mesocarp (SAM) and kernel (SAK) reflected distinct temporal or spatial expression patterns for PsARF genes. Additionally, based on the expressed data from fruit and seed development of multiple plant species, we identified 1514 ARF-correlated genes using weighted gene co-expression network analysis (WGCNA). And the major portion of ARF-correlated gene was characterized to be involved in protein, nucleic acid and carbohydrate metabolic, transport and regulatory processes.

CONCLUSIONS

In summary, we systematically and comprehensively analyzed the structure, expression pattern and co-expression network of ARF gene family in P. sibirica. All our findings provide theoretical foundation for the PsARF gene family and will pave the way for elucidating the precise role of PsARF genes in SAM and SAK development.

Integrated analysis of 454 and Illumina transcriptomic sequencing characterizes carbon flux and energy source for fatty acid synthesis in developing Lindera glauca fruits for woody biodiesel

BACKGROUND

Lindera glauca fruit with high quality and quantity of oil has emerged as a novel potential source of biodiesel in China, but the molecular regulatory mechanism of carbon flux and energy source for oil biosynthesis in developing fruits is still unknown. To better develop fruit oils of L. glauca as woody biodiesel, a combination of two different sequencing platforms (454 and Illumina) and qRT-PCR analysis was used to define a minimal reference transcriptome of developing L. glauca fruits, and to construct carbon and energy metabolic model for regulation of carbon partitioning and energy supply for FA biosynthesis and oil accumulation.

RESULTS

We first analyzed the dynamic patterns of growth tendency, oil content, FA compositions, biodiesel properties, and the contents of ATP and pyridine nucleotide of L. glauca fruits from seven different developing stages. Comprehensive characterization of transcriptome of the developing L. glauca fruit was performed using a combination of two different next-generation sequencing platforms, of which three representative fruit samples (50, 125, and 150 DAF) and one mixed sample from seven developing stages were selected for Illumina and 454 sequencing, respectively. The unigenes separately obtained from long and short reads (201, and 259, respectively, in total) were reconciled using TGICL software, resulting in a total of 60,031 unigenes (mean length = 1061.95 bp) to describe a transcriptome for developing L. glauca fruits. Notably, 198 genes were annotated for photosynthesis, sucrose cleavage, carbon allocation, metabolite transport, acetyl-CoA formation, oil synthesis, and energy metabolism, among which some specific transporters, transcription factors, and enzymes were identified to be implicated in carbon partitioning and energy source for oil synthesis by an integrated analysis of transcriptomic sequencing and qRT-PCR. Importantly, the carbon and energy metabolic model was well established for oil biosynthesis of developing L. glauca fruits, which could help to reveal the molecular regulatory mechanism of the increased oil production in developing fruits.

CONCLUSIONS

This study presents for the first time the application of an integrated two different sequencing analyses (Illumina and 454) and qRT-PCR detection to define a minimal reference transcriptome for developing L. glauca fruits, and to elucidate the molecular regulatory mechanism of carbon flux control and energy provision for oil synthesis. Our results will provide a valuable resource for future fundamental and applied research on the woody biodiesel plants.

Analysis of transcriptome in hickory (Carya cathayensis), and uncover the dynamics in the hormonal signaling pathway during graft process

BACKGROUND

Hickory (Carya cathayensis), a woody plant with high nutritional and economic value, is widely planted in China. Due to its long juvenile phase, grafting is a useful technique for large-scale cultivation of hickory. To reveal the molecular mechanism during the graft process, we sequenced the transcriptomes of graft union in hickory.

RESULTS

In our study, six RNA-seq libraries yielded a total of 83,676,860 clean short reads comprising 4.19 Gb of sequence data. A large number of differentially expressed genes (DEGs) at three time points during the graft process were identified. In detail, 777 DEGs in the 7 d vs 0 d (day after grafting) comparison were classified into 11 enriched Gene Ontology (GO) categories, and 262 DEGs in the 14 d vs 0 d comparison were classified into 15 enriched GO categories. Furthermore, an overview of the PPI network was constructed by these DEGs. In addition, 20 genes related to the auxin-and cytokinin-signaling pathways were identified, and some were validated by qRT-PCR analysis.

CONCLUSIONS

Our comprehensive analysis provides basic information on the candidate genes and hormone signaling pathways involved in the graft process in hickory and other woody plants.

Transcriptome analysis revealed the dynamic oil accumulation in Symplocos paniculata fruit

BACKGROUND

Symplocos paniculata, asiatic sweetleaf or sapphire berry, is a widespread shrub or small tree from Symplocaceae with high oil content and excellent fatty acid composition in fruit. It has been used as feedstocks for biodiesel and cooking oil production in China. Little transcriptome information is available on the regulatory molecular mechanism of oil accumulation at different fruit development stages.

RESULTS

The transcriptome at four different stages of fruit development (10, 80,140, and 170 days after flowering) of S. paniculata were analyzed. Approximately 28 million high quality clean reads were generated. These reads were trimmed and assembled into 182,904 non-redundant putative transcripts with a mean length of 592.91 bp and N50 length of 785 bp, respectively. Based on the functional annotation through Basic Local Alignment Search Tool (BLAST) with public protein database, the key enzymes involved in lipid metabolism were identified, and a schematic diagram of the pathway and temporal expression patterns of lipid metabolism was established. About 13,939 differentially expressed unigenes (DEGs) were screened out using differentially expressed sequencing (DESeq) method. The transcriptional regulatory patterns of the identified enzymes were highly related to the dynamic oil accumulation along with the fruit development of S. paniculata. In addition, quantitative real-time PCR (qRT-PCR) of six vital genes was significantly correlated with DESeq data.

CONCLUSIONS

The transcriptome sequences obtained and deposited in NCBI would enrich the public database and provide an unprecedented resource for the discovery of the genes associated with lipid metabolism pathway in S. paniculata. Results in this study will lay the foundation for exploring transcriptional regulatory profiles, elucidating molecular regulatory mechanisms, and accelerating genetic engineering process to improve the yield and quality of seed oil of S. paniculata.

Integrated mRNA and miRNA transcriptome reveal a cross-talk between developing response and hormone signaling for the seed kernels of Siberian apricot

Recently, our transcriptomic analysis has identified some functional genes responsible for oil biosynthesis in developing SASK, yet miRNA-mediated regulation for SASK development and oil accumulation is poorly understood. Here, 3 representative periods of 10, 30 and 60 DAF were selected for sRNA sequencing based on the dynamic patterns of growth tendency and oil content of developing SASK. By miRNA transcriptomic analysis, we characterized 296 known and 44 novel miRNAs in developing SASK, among which 36 known and 6 novel miRNAs respond specifically to developing SASK. Importantly, we performed an integrated analysis of mRNA and miRNA transcriptome as well as qRT-PCR detection to identify some key miRNAs and their targets (miR156-SPL, miR160-ARF18, miR164-NAC1, miR171h-SCL6, miR172-AP2, miR395-AUX22B, miR530-P2C37, miR393h-TIR1/AFB2 and psi-miRn5-SnRK2A) potentially involved in developing response and hormone signaling of SASK. Our results provide new insights into the important regulatory function of cross-talk between development response and hormone signaling for SASK oil accumulation.

Gene expression profiling during seed-filling process in peanut with emphasis on oil biosynthesis networks

Pod-filling is an important stage of peanut (Arachis hypogaea) seed development. It is partially controlled by genetic factors, as cultivars considerably vary in pod-filling potential. Here, a study was done to detect changes in mRNA levels that accompany pod-filling processes. Four seed developmental stages were sampled from two peanut genotypes differing in their oil content and pod-filling potential. Transcriptome data were generated by RNA-Seq and explored with respect to genic and subgenomic patterns of expression. Very dynamic transcriptomic changes occurred during seed development in both genotypes. Yet, general higher expression rates of transcripts and an enrichment in processes involved "energy generation" and "primary metabolites" were observed in the genotype with the better pod-filling ("Hanoch"). A dataset of 584 oil-related genes was assembled and analyzed, resulting in several lipid metabolic processes highly expressed in Hanoch, including oil storage and FA synthesis/elongation. Homoeolog-specific gene expression analysis revealed that both subgenomes contribute to the oil genes expression. Yet, biases were observed in particular parts of the pathway with possible biological meaning, presumably explaining the genotypic variation in oil biosynthesis and pod-filling. This study provides baseline information and a resource that may be used to understand development and oil biosynthesis in the peanut seeds.