Flower color is one of the most important features of ornamental plants. Its development and regulation are influenced by many internal and external factors. Therefore, understanding the mechanism of color development and its regulation provides an important theoretical basis and premise for the cultivation and improvement of new color varieties of ornamental plants. This paper outlines the functions of petal tissue structure, as well as the distribution and type of pigments, especially anthocyanins, in color development. The progress of research on flower color regulation with a focus on physical factors, chemical factors, and genetic engineering is introduced. The shortcomings of flower color research and the potential directions for future development are explored to provide a broad background for flower color improvements in ornamental plants.

Herbaceous peony (Paeonia lactiflora Pall.) is an important ornamental plant which contains different flower colors. In this paper, eight genes encoding phenylalanine ammonialyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3'-hydroxylase (F3'H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), UDP-glucose: flavonoid 3-o-glucosyltransferase (UF3GT) were isolated. Moreover, the expression patterns of these eight genes and UF5GT in the flowers were investigated in three cultivars, that is, 'Hongyanzhenghui', 'Yulouhongxing' and 'Huangjinlun' with purplish-red, white and yellow flower respectively. Furthermore, flavonoid accumulation in the flowers was also analyzed. The results showed that in different organs, most of genes expressed higher in flowers than in other organs. During the development of flowers, all genes could be divided into four groups. The first group (PlPAL) was highly expressed in S1 and S4. The second group (PlCHS and PlCHI) was at a high expression level throughout the whole developmental stages. The third group (PlF3H, PlF3'H, PlDFR, PlANS and PlUF5GT) gradually decreased with the development of flowers. The fourth group (PlUF3GT) gradually increased during the flower development. In addition, anthoxanthins and anthocyanins were detected in 'Hongyanzhenghui' and 'Yulouhongxing', chalcones and anthoxanthins were found in 'Huangjinlun'. When different color flowers were concerned, low expression level of PlCHI induced most of the substrate accumulation in the form of chalcones and displaying yellow, changing a small part of substrates to anthoxanthins, and there was no anthocyanin synthesis in 'Huangjinlun' because of low expression level of DFR. In 'Yulouhongxing', massive expressions of upstream genes and low expression of DFR caused synthesis of a great deal of anthoxanthins and a small amount of colorless anthocyanins. In 'Hongyanzhenghui', a large number of colored anthocyanins were changed from anthoxanthins because of PlDFR, PlANS and PlUF3GT high expressions. These results would provide us a theoretical basis to understand the formation of P. lactiflora flower colors.

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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.

Carotenoids in the peel and the flesh of persimmon fruit were identified, and the contents of carotenoids in the fleshes of 46 different persimmon cultivars were analyzed. The results indicated that 31 specific carotenoids were detected in both cultivars of persimmons, among which nine specific carotenoids were characterized. β-Cryptoxanthin was the most abundant carotenoid among all individual components in both the peel and the flesh, accounting for about 20-30% of the total carotenoids in both cultivars. The contents of total carotenoids in the fleshes of different persimmon cultivars were between 194.61 µg/100g FW and 1,566.30 µg/100g FW. Zeaxanthin was also the most abundant in all persimmon fleshes besides β-Cryptoxanthin, and the total amount of these two components accounted for 37.84-85.11% of the total carotenoids. The RE values in the fleshes of different cultivars also differed greatly. Besides, the stage of maturation was also important factor which could influence the carotenoid content and RE value in the fleshes.