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BackgroundHerbaceous peony (Paeonia lactiflora Pall.) is a traditional flower in China and a wedding attractive flower in worldwide. In its flower colour, yellow is the rarest which is ten times the price of the other colours. However, the breeding of new yellow P. lactiflora varieties using genetic engineering is severely limited due to the little-known biochemical and molecular mechanisms underlying its characteristic formation.ResultsIn this study, two cDNA libraries generated from P. lactiflora chimaera with red outer-petal and yellow inner-petal were sequenced using an Illumina HiSeq™ 2000 platform. 66,179,398 and 65,481,444 total raw reads from red outer-petal and yellow inner-petal cDNA libraries were generated, which were assembled into 61,431 and 70,359 Unigenes with an average length of 628 and 617 nt, respectively. Moreover, 61,408 non-redundant All-unigenes were obtained, with 37,511 All-unigenes (61.08%) annotated in public databases. In addition, 6,345 All-unigenes were differentially expressed between the red outer-petal and yellow inner-petal, with 3,899 up-regulated and 2,446 down-regulated All-unigenes, and the flavonoid metabolic pathway related to colour development was identified using the Kyoto encyclopedia of genes and genomes database (KEGG). Subsequently, the expression patterns of 10 candidate differentially expressed genes (DEGs) involved in the flavonoid metabolic pathway were examined, and flavonoids were qualitatively and quantitatively analysed. Numerous anthoxanthins (flavone and flavonol) and a few anthocyanins were detected in the yellow inner-petal, which were all lower than those in the red outer-petal due to the low expression levels of the phenylalanine ammonialyase gene (PlPAL), flavonol synthase gene (PlFLS), dihydroflavonol 4-reductase gene (PlDFR), anthocyanidin synthase gene (PlANS), anthocyanidin 3-O-glucosyltransferase gene (Pl3GT) and anthocyanidin 5-O-glucosyltransferase gene (Pl5GT).ConclusionTranscriptome sequencing (RNA-Seq) analysis based on the high throughput sequencing technology was an efficient approach to identify critical genes in P. lactiflora and other non-model plants. The flavonoid metabolic pathway and glucide metabolic pathway were identified as relatived yellow formation in P. lactiflora, PlPAL, PlFLS, PlDFR, PlANS, Pl3GT and Pl5GT were selected as potential candidates involved in flavonoid metabolic pathway, which inducing inhibition of anthocyanin biosynthesis mediated yellow formation in P. lactiflora. This study could lay a theoretical foundation for breeding new yellow P. lactiflora varieties.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-689) contains supplementary material, which is available to authorized users.

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Herbaceous peony (Paeonia lactiflora Pall.) seed oil (HPSO) was extracted from seeds by ultrasonic‐assisted extraction (UAE). Changes in the oil yield, fatty acid (FA) composition, retinol and tocopherol (α‐, γ‐, and δ‐tocopherol) contents of HPSO at the different developmental stages and in tested cultivars were examined, and the microscopic structure of HPSO droplets was also observed. The results showed that the HPSO yield increased with the seed development and reached its maximum level at the mature stage with values from 29.04 to 34.98% for different cultivars. The unsaturated fatty acid (UFA) contents were between 88.36 to 94.58%. Among the UFAs, the contents of oleic acid (27.19–45.06%), linoleic acid (20.59–37.59%), and α‐linolenic acid (13.59–30.87%) were relatively high. The average γ‐tocopherol content was 337.47 ± 57.42 µg/g, accounting for approximately 92.97% of the total tocopherol content. Transmission electron microscopy (TEM) observations of the HPSO microscopic structures indicated that the quantity and size of the oil bodies increased with the development of endosperm cells in P. lactiflora. This report was the first to study the HPSO, and the results will provide theoretical guidance for the exploitation and utilization of P. lactiflora resources. The content of UFA (A) was more than 90% in HPSO, and the content of γ‐tocopherol was 353.67 ± 0.22 µg/g, accounting for about 93% of total tocopherols content (B).

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