Abstract
Plants with the flower color phenotype of double-color flowers are very precious and attractive and can usually be regarded as valuable germplasm resources for studying and improving flower color. This paper summarizes the coloring mechanism of double-color flowers in plants from three aspects: the formation of double-color flowers, the physiological factors affecting the coloring difference of double-color flowers, and the molecular mechanism affecting the coloring difference of double-color flowers, to provide a theoretical reference for the in-depth study of the coloring mechanism and molecular breeding of double-color flowers in the future.
In plants, especially ornamentals, flower color is a very important ornamental trait (Han et al., 2022). Among the many flower colors, most of them are monochromatic color in the plant world, but a few are double-color. The definition of double-color flowers (Fig. 1), in a narrow sense, usually refers to petals with two or more colors on the same flower. In a broad sense, it also includes flowers with two or more colors on the same plant.
Some reported plant species with double-color flower patterns. (A–E) Nymphaea ‘Fen Ma Nao’, Wu et al. (2018); Narcissus pseudonarcissus, Hunter et al. (2011); Petunia hybrida, Chuck et al. (1993); Clarkia gracilis, Martins et al. (2013); Lilium ‘Tiny Padhye’, Xu et al. (2017). (F–J) Nelumbo nucifera ‘Dasajin’, Deng et al. (2022); Viola ×wittrockiana ‘Mengdie’, Wang et al. (2022); Prunus persica f. versicolor, Chen et al. (2014); Paeonia lactiflora ‘Jinhui’, Zhao et al. (2017a); Paeonia suffruticosa ‘Shima Nishiki’, Zhang et al. (2018b). (K–O) Paeonia suffruticosa ‘Er Qiao’, Zhang et al. (2020); Lilium cernuum var. Album, Yamagishi (2020); Phalaenopsis ‘Panda’, Zhao et al. (2019); Mirabilis jalapa ‘Four o’clock’, Suzuki et al. (2014); Petunia hybrida, Morita et al. (2012). (P–S) Tricyrtis ‘Shinonome’, Kamiishi et al. (2012); Oncidium ‘Gower Ramsey’, Liu et al. (2012); Prunus mume ‘Fuban Tiaozhi’, Jiang et al. (2020); Prunus persica ‘Sahong Tao’, Wu et al. (2020).
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
Some reported plant species with double-color flower patterns. (A–E) Nymphaea ‘Fen Ma Nao’, Wu et al. (2018); Narcissus pseudonarcissus, Hunter et al. (2011); Petunia hybrida, Chuck et al. (1993); Clarkia gracilis, Martins et al. (2013); Lilium ‘Tiny Padhye’, Xu et al. (2017). (F–J) Nelumbo nucifera ‘Dasajin’, Deng et al. (2022); Viola ×wittrockiana ‘Mengdie’, Wang et al. (2022); Prunus persica f. versicolor, Chen et al. (2014); Paeonia lactiflora ‘Jinhui’, Zhao et al. (2017a); Paeonia suffruticosa ‘Shima Nishiki’, Zhang et al. (2018b). (K–O) Paeonia suffruticosa ‘Er Qiao’, Zhang et al. (2020); Lilium cernuum var. Album, Yamagishi (2020); Phalaenopsis ‘Panda’, Zhao et al. (2019); Mirabilis jalapa ‘Four o’clock’, Suzuki et al. (2014); Petunia hybrida, Morita et al. (2012). (P–S) Tricyrtis ‘Shinonome’, Kamiishi et al. (2012); Oncidium ‘Gower Ramsey’, Liu et al. (2012); Prunus mume ‘Fuban Tiaozhi’, Jiang et al. (2020); Prunus persica ‘Sahong Tao’, Wu et al. (2020).
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
Some reported plant species with double-color flower patterns. (A–E) Nymphaea ‘Fen Ma Nao’, Wu et al. (2018); Narcissus pseudonarcissus, Hunter et al. (2011); Petunia hybrida, Chuck et al. (1993); Clarkia gracilis, Martins et al. (2013); Lilium ‘Tiny Padhye’, Xu et al. (2017). (F–J) Nelumbo nucifera ‘Dasajin’, Deng et al. (2022); Viola ×wittrockiana ‘Mengdie’, Wang et al. (2022); Prunus persica f. versicolor, Chen et al. (2014); Paeonia lactiflora ‘Jinhui’, Zhao et al. (2017a); Paeonia suffruticosa ‘Shima Nishiki’, Zhang et al. (2018b). (K–O) Paeonia suffruticosa ‘Er Qiao’, Zhang et al. (2020); Lilium cernuum var. Album, Yamagishi (2020); Phalaenopsis ‘Panda’, Zhao et al. (2019); Mirabilis jalapa ‘Four o’clock’, Suzuki et al. (2014); Petunia hybrida, Morita et al. (2012). (P–S) Tricyrtis ‘Shinonome’, Kamiishi et al. (2012); Oncidium ‘Gower Ramsey’, Liu et al. (2012); Prunus mume ‘Fuban Tiaozhi’, Jiang et al. (2020); Prunus persica ‘Sahong Tao’, Wu et al. (2020).
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
The double-color flowers in many plants are generally considered a kind of chimera in the industry of horticulture, forest, and agriculture. The flowers of this chimera usually have a colorful and prominent phenotype and are often favored by many consumers in the flower market (Li and He, 2005; Noman et al., 2017; Wang et al., 2022; Wu et al., 2020). Therefore, it is not hard to understand that the research and cultivation of these unique double-color flowers has also become one of the main directions of many researchers and breeding workers (Li et al., 2005; Zhang et al., 2019, 2022).
The exploration and explanation of the coloring mechanism of double-color flowers in plants plays a key role in breeding this color phenotype. Therefore, conducting in-depth relevant research will have important theoretical significance and application value for regulating and creating these distinctive colors in actual production. Different plants with double-color flowers usually have different coloring mechanisms. This paper focuses on combining the current research advances related to double-color flowers from the physiological and molecular levels (especially from the molecular level) and hopes to provide a significant reference for relevant researchers to reveal the coloring mechanism of double-color flowers more accurately, objectively, and comprehensively, and cultivate new varieties of double-color flowers in the future.
Formation of Double-color Flowers in Plants
In many plants, there is a double-color phenotype for flower color. Many of them are obtained by natural selection, artificial hybridization, radiation mutation, etc. Zhao and Zhang (1992) found one flower and two buds with yellow petals embedded in the background of their orange-red petals in the “104-58” planting garden of hybrid chrysanthemum, and this chimera with double-color flowers was successfully isolated through tissue culture technology. Liu and Zhang (2009) performed radiation mutation of Gladiolus hybridus ‘Spic and span’ by using 60Co γ. Mutant plants with the phenotype of double-color (pink and white) flowers were selected, and the M3 generation with the same variant characters was obtained. Song and Zhu (2010) performed radiation mutation of the self-bred seeds of groundcover chrysanthemum cultivars by using Fe+ injection. A chimera with double-color phenotype was found in the injected plants, and the plant lines with the same characteristics as the mother plant were isolated through tissue culture technology. Li et al. (2010) found two variant branches of flowers/leaves in Loropetalum chinense ‘Mizhi Meihong’ and isolated a bud mutation type with double-color (milky white and pink) flowers through cutting propagation. Wu et al. (2018) obtained a new waterlily cultivar ‘Fen Ma Nao’ with double-color flowers (light red-purple tip and yellow-white base) via artificial hybridization.
Some studies have shown that virus infection can also lead to the phenotypic formation of double-color flowers. Duan and Cai (1998) found that the double-color flowers of four ornamental plants (Dianthus caryophyllus, Matthiola incana, Gladiolus hybridus, and Papaver rhoeas) can be caused by different viral infections. Hunter et al. (2011) found that Narcissus mosaic virus can lead to the phenotype of double-color (yellow and white) flowers in Narcissus pseudonarcissus.
In addition, the double-color flower phenotype in plants can be obtained by genetic transformation method. By inserting the Ac transposon of maize into the Ph6 gene of petunia, it was found that the original red flower of petunia showed a double-color phenotype (Chuck et al., 1993). Liu et al. (2001) introduced the modified vector of transcription factor R (transposon Tag1 inserted between CaMV35s and R genes) into tobacco and found that these flowers showed a variety of double-color phenotypes in transgenic tobacco plants. Tao et al. (2006) introduced the silencing vector of the chalcone synthase (CHS) gene into petunia and found that the flower color faded in transgenic plants and changed from monochrome color to a double color. Han et al. (2012) introduced the anthocyanidin reductase (ANR) gene of apple into tobacco and found that these flowers in transgenic lines could show a double-color (red and white) phenotype.
Physiological Factors Affecting the Color Difference of Double-color Flowers
An in-depth understanding of the causes of these double-color flowers will help people better regulate and create such chimeric flower colors. In plants, there are many kinds of pigments, which are generally divided into four categories: flavonoids, carotenoids, betalains, and chlorophyll. Flavonoids are very important pigments that extensively affect flower color. Among them, anthocyanins contribute the most (Davies et al., 2012; Grotewold, 2006; Nishihara and Nakatsuka, 2011; Wang et al., 2021; Zhang et al., 2018a, 2018b). In addition to anthocyanins, many physiological factors, such as vacuolar pH value (Quattrocchio et al., 2006; Yoshida et al., 2005), metal element content (Schreiber et al., 2011; Shoji et al., 2010), upper epidermal cell shape (Baumann et al., 2007; Deng et al., 2022; Noda et al., 1994; Zhang et al., 2018b), and soluble sugar content (Zhang et al., 2015; Zheng et al., 2009), can also affect the presentation of flower color to a certain extent.
It is well known that vacuoles are the main storage areas of plant pigments, especially flavonoids. Therefore, petal color is also affected by the physiological environment in the vacuole. Generally, with the increase in vacuolar pH value, some plant flower organs will change from pink/red to purple/blue (Zhang et al., 2021). For example, the sepals of hydrangea have only one anthocyanin (delphinidin-3-O-glucoside), but the color showed various colors from red to blue, which is mainly attributed to the change in vacuole pH and the collection effect with AI3+ in acidic soils (Avila-Rostant et al., 2010; Yoshida et al., 2009). For the upper epidermal cell shape, it is generally believed that a conical shape will increase the proportion of incident light entering petal epidermal cells, thus deepening the color of petals (Noda et al., 1994). In plants, soluble sugar is usually an important substance necessary for anthocyanin biosynthesis (Zhang et al., 2009; Zheng et al., 2015), and its content may also affect petal color.
At present, many studies have shown that the physiological basis for the formation of double-color flowers is also mostly the differential accumulation of pigment components (such as flavonoids, especially for anthocyanins) in different flower color regions (Table 1). Through high-performance liquid chromatography (HPLC) analysis, Chiou and Yeh (2008) found that malvidin-3-O-galactoside, cyanidin 3-O-glucoside, peonidin-3-O-glucoside, and delphinidin-3-O-glucoside were the main anthocyanins in the red spot area of Oncidium petals, but these components were not detected in the yellow background area. Martins et al. (2013) analyzed the anthocyanins in the purple-red spot and pink background area of the petals of Clarkia gracilis by HPLC, and found that the pigment components in the spot area were cyanidin/peonidin-based anthocyanins, whereas those in the background area were malvidin-based anthocyanins. Xu et al. (2017) studied the purple and white areas of double-color flowers in the Asiatic hybrid lily cultivar Tiny Padhye, and found that the difference in flower color was mainly attributed to cyanidin 3-O-β-rutinoside. Deng et al. (2022) performed relevant analysis of double-color (red and white) flowers in Lotus ‘Dasajin’, and found that the difference in anthocyanin content was an important reason for the flower color difference. Meanwhile, they believed that the abnormal thylakoid development in the red part of the petal led to the accumulation of anthocyanin in this area. Wang et al. (2022) found that there was no significant difference in carotenoid content between the yellow spotless area and gray-purple spot area of double-color flowers in Viola ×wittrockiana ‘Mengdie’, but there was a significant difference in anthocyanin content.
Summary on differential accumulation of key pigment components and the related genes possibly involved in double-color flowers in different plants.
Molecular Mechanism Affecting the Color Difference of Double-color Flowers
At present, the flavonoid biosynthetic pathway (Fig. 2) is a secondary metabolic pathway that has been clearly studied and is well known to be highly conserved in many plants (Nishihara and Nakatsuka, 2011; Shi et al., 2014; Wang et al., 2021; Zhang and Lu, 2016; Zhang et al., 2012, 2019). Generally, flavonoids are biosynthesized in the cytoplasm and then transferred to the vacuole for storage before petal coloring. Therefore, this usually involves some flavonoid transporters that may also affect flower color, such as multidrug and toxic extrusion (MATE) and glutathione S-transferase (GST) (Cao et al., 2021; Chen et al., 2015; Gani et al., 2022; Gao et al., 2016a; Gomez et al., 2009; Han et al., 2022).
A general schematic diagram of the flavonoid biosynthetic pathway closely related to double-color flowers in plants. PAL = phenylalanine ammonia-lyase; C4H = cinnamate 4-hydroxylase; 4CL = 4-coumarate:CoA ligase; CHS = chalcone synthase; CHI = chalcone isomerase; F3H = flavanone 3-hydroxylase; F3'H = flavonoid 3'-hydroxylase; F3'5'H = flavonoid 3' = 5'-hydroxylase; DFR = dihydroflavonol 4-reductase; ANS = anthocyanidin synthase; FNS = flavone synthase; FLS = flavonol synthase; ANR = anthocyanidin reductase; AOMT = anthocyanin O-methyltransferase; UFGT = UDP-glucose: flavonoid glucosyltransferase; MATE = multidrug and toxic extrusion; GST = glutathione S-transferase.
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
A general schematic diagram of the flavonoid biosynthetic pathway closely related to double-color flowers in plants. PAL = phenylalanine ammonia-lyase; C4H = cinnamate 4-hydroxylase; 4CL = 4-coumarate:CoA ligase; CHS = chalcone synthase; CHI = chalcone isomerase; F3H = flavanone 3-hydroxylase; F3'H = flavonoid 3'-hydroxylase; F3'5'H = flavonoid 3' = 5'-hydroxylase; DFR = dihydroflavonol 4-reductase; ANS = anthocyanidin synthase; FNS = flavone synthase; FLS = flavonol synthase; ANR = anthocyanidin reductase; AOMT = anthocyanin O-methyltransferase; UFGT = UDP-glucose: flavonoid glucosyltransferase; MATE = multidrug and toxic extrusion; GST = glutathione S-transferase.
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
A general schematic diagram of the flavonoid biosynthetic pathway closely related to double-color flowers in plants. PAL = phenylalanine ammonia-lyase; C4H = cinnamate 4-hydroxylase; 4CL = 4-coumarate:CoA ligase; CHS = chalcone synthase; CHI = chalcone isomerase; F3H = flavanone 3-hydroxylase; F3'H = flavonoid 3'-hydroxylase; F3'5'H = flavonoid 3' = 5'-hydroxylase; DFR = dihydroflavonol 4-reductase; ANS = anthocyanidin synthase; FNS = flavone synthase; FLS = flavonol synthase; ANR = anthocyanidin reductase; AOMT = anthocyanin O-methyltransferase; UFGT = UDP-glucose: flavonoid glucosyltransferase; MATE = multidrug and toxic extrusion; GST = glutathione S-transferase.
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
Many existing studies have shown that the most direct molecular mechanism for the color difference of double-color flowers is usually the differential expression of one or more key structural genes related to flavonoid biosynthesis, and the differential expression of structural genes is usually caused by the differential expression of upstream regulatory genes [such as transcription factors or micro RNAs (miRNAs)] (Luan et al., 2022; Nakatsuka et al., 2005; Wu et al., 2016; Zhang et al., 2018a, 2022) (Table 1). However, in fact, the molecular mechanism of the color difference of double-color flowers is often relatively complex, and the reasons are different in different plants. Based on the current relevant research at home and abroad, the preliminary molecular mechanism of double-color flowers can be summarized into four aspects: tissue-specific expression of genes, insertion of transposons or partial fragments, RNA interference, and DNA methylation.
Tissue-specific expression of genes.
At the molecular level, the tissue-specific expression of structural genes or regulatory factors related to flavonoid (especially anthocyanin) biosynthesis is usually the direct reason for the color difference of double-color flowers in plants (Lalusin et al., 2006; Zhang et al., 2018a, 2018b). For structural genes related to flavonoid biosynthesis, Chen et al. (2014) found that the high expression of cinnamate 4-hydroxylase (C4H), CHS, and flavanone 3-hydroxylase (F3H) genes in red flowers may be an important reason for the color difference between double-color (red and white) flowers in Prunus persica f. versicolor. Zhao et al. (2014) screened six differentially expressed genes (PlPAL, PlFLS, PlDFR, PlANS, Pl3GT, and Pl5GT) through relevant analysis of double-color (red and yellow) flowers in Paeonia lactiflora ‘Jinhui’, and believed that the low expression of these genes may be an important reason for the formation of yellow petals. Yin et al. (2019) further studied the protein level of double-color (red and white) flowers in Prunus persica f. versicolor but found that the significant upregulation of anthocyanidin synthase (ANS) and GST protein activities in red petals may be an important reason for the color difference. Zhang et al. (2020) found that the higher expression of the PsFLS gene in pink petals may be one of the important reasons for the color difference of double-color (purple and pink) flowers in Paeonia suffruticosa ‘Er Qiao’. Zhang et al. (2018a, 2018b) found that the higher differential expression of PsDFR in double-color (red and pink) flowers should be the key structural gene for the color difference in P. suffruticosa ‘Shima Nishiki’.
For transcription factors (TFs) related to flavonoid biosynthesis, various studies have found that they mainly include v-myb avian myeloblastosis viral oncogene homolog (MYB), basic helix-loop-helix (bHLH), WD40-repeat protein (WD40), SQUAMOSA promoter-binding-like (SPL), phytochrome interacting factor, lateral organ boundaries domain, etc (Hsu et al., 2015; Li et al., 2017; Luo et al., 2022; Pashkovskiy et al., 2021; Qian et al., 2017; Zhang et al., 2019). Among them, the former three TFs have been the most widely and intensively studied until now, and the regulatory effect of MYB TFs (especially for R2R3-MYB) on flower color is also regarded as the most important (Dubos et al., 2010; Hichri et al., 2011; Zhao and Tao, 2015; Zhang et al., 2019). In plants, MYB TFs can individually regulate anthocyanin structural genes and can form MYB-bHLH (MB), MYB-WD40 (MW), or MYB-bHLH-WD40 (MBW) protein complexes through interactions to jointly regulate the expression of structural genes (Albert et al., 2014; Qi et al., 2020; Schaart et al., 2013). Chiou and Yeh (2008) found that the differential expression of the OgMYB1 gene is an important reason for the color difference between red spot and yellow background areas of Oncidium petals. Suzuki et al. (2016) studied the Asiatic hybrid lily cultivar ‘Lollypop’ and found that the specific expression of LhMYB12 was closely related to the coloring difference between the base and upper parts of the double-color flowers. Yamagishi (2020) found that the specific expression of LcMYB12 was closely related to the coloring difference of double-color (pink and white) flowers in Lilium cernuum var. album.
In recent years, studies in many plants have shown that some miRNAs (miR156, miR828, miR858, miR395, miR827, etc.) can directly affect their target genes (such as some TFs involved in the regulation of flavonoid biosynthesis), then affect the expression level of key structural genes related to flavonoid biosynthesis, and ultimately regulate flower color differences (Bonar et al., 2018; Gou et al., 2011; Li et al., 2020; Pashkovskiy et al., 2021; Tirumalai et al., 2019; Yamagishi and Sakai, 2020; Zhang et al., 2022). Zhao et al. (2017a, 2017b) found that the specific expressions of miR156e-3p and SPL1 in the miR156e-3p/SPL1 regulation module may be an important reason for the yellow formation of double-color flowers in P. lactiflora ‘Jinhui’. Zhao et al. (2019) found that the specific expression of miR156g, miR858, and their corresponding target genes PeMYB7 and PeMYB11 in the spotted and nonspotted parts of double-color flowers may be an important regulatory reason for the flower color difference in Phalaenopsis ‘Panda’. Yamagishi and Sakai (2020) found that the specific expressions of miR828 and MYB12 in the miR828/MYB12 regulation module are closely related to the coloring of double-color flowers in five Asiatic hybrid lily bicolor cultivars. Zhang et al. (2022) found that the specific expressions of miR858 and PsMYB12L in the miR858/PsMYB12L module may be one of the important reasons for regulating the color difference of its double-color flowers in P. suffruticosa ‘Shima Nishiki’.
Insertion of transposons or partial fragments.
Li et al. (2005) found that the chromosome numbers of the double-color (purple and yellow) flowers in chrysanthemum were exactly the same and speculated that the reason for this chimeric flower color phenotype was the transposon insertion of the pigment biosynthesis gene. Wang et al. (2012) found that when people grafted and sowed with the chimera cultivar ‘Sahong Tao’ in Prunus persica, the flowering of its offspring was still a chimeric color and concluded that this double-color phenotype may be also formed by transposon insertion.
Transposons are also called “jumping factors.” They were first discovered in corn by McClintock (1948). Since then, researchers have found transposons in many ornamental plants, such as Antirrhinum majus, Petunia hybrida, and Dianthus caryophyllus. Transposon is actually a mobile DNA sequence in the genome that can “jump” from one position of the chromosome to another (Gao et al., 2016b). Transposons can lead to the inactivation of inserted genes. In addition, because of their “jumping” trait, transposons usually lead to the appearance of irregular chimeric colors. The distribution of chimeric color regions is usually related to the time and frequency of transposon insertion (Li et al., 2005; Zhang et al., 2018a). Most transposon insertions generally exist in the exons, introns, and promoter regions of some structural genes related to flavonoid biosynthesis, and sometimes in some TFs related to flavonoid biosynthesis.
Itoh et al. (2002) found that an Ac/Ds transposon, dtdic1, was inserted into the exon regions of the DcDFR and DcCHI genes, respectively, which may be the key reason for the formation of white flowers with red splotches/fan stripes and yellow flowers with white splotches/fan stripes. Takahashi et al. (2012) studied the wild soybean cultivar ‘B00146-m’ and found that a CACTA-type transposon, Tgs1, was inserted into the exon region of the GsF3'5'H gene, which led to the formation of double-color (purple and white) flowers. Sasaki et al. (2012) found that a CACTA-type transposon, dTac1, was inserted into the intron region of its DcGSTF2 gene, resulting in dark-pink stripes on the light-pink petals in Dianthus caryophyllus ‘Daisy VP’. Suzuki et al. (2014) studied the Mirabilis jalapa cultivar ‘Four o’clock’ and found that a dTmj1 transposon was inserted into the intron region of its MjCYP76AD3 gene, resulting in a chimeric phenotype of double-color (purple and yellow) flowers. Sato et al. (2011) found that a transposon belonging to the hAT superfamily was inserted into the promoter region of its SiF3'5H gene, resulting in the double-color phenotype of blue splotches on pink petals in the Saintpaulia cultivar Thamires. Furthermore, Nishijima et al. (2013) studied the mutant ‘Flecked’ of Torenia fournieri and found that an En/Spm transposon, Ttf1, was inserted into the intron region of TfMYB1 TFs, resulting in the double-color phenotype of a light-blue background and purple splotches on the petals.
In addition to the preceding cases of transposon insertion, the partial fragment insertion of some bases will also lead to the phenotype of double-color flowers. Zhang et al. (2020) found that there was a 6-base pair base (GCGGCG) insertion in the coding sequence (CDS) region of the flavonoid 3'-hydroxylase (F3'H) gene in pink flowers and concluded that this may be one of the important reasons for the color difference of double-color (purple and pink) flowers in P. suffruticosa ‘Er Qiao’.
RNA interference.
RNA interference can also affect flower color (Tanaka et al., 2008) and usually refers to small interfering RNA (siRNA) mediating posttranscriptional gene silencing (PTGS). The CHS gene, as its target gene mediated by siRNA, has been extensively studied. Ohno et al. (2011, 2018) found that the white region of its double-color (red and white) flowers was probably caused by siRNA-mediated posttranscriptional silencing of the DvCHS2 gene through a comprehensive study in Dahlia variabilis ‘Yuino’. Morita et al. (2012) studied the cultivars of double-color flowers of ‘Picotee’ and ‘Star’ in P. hybrida, and found that the posttranscriptional silencing of the PhCHS-A1 and PhCHS-A2 genes caused by siRNA interference may be a key reason for this flower color phenotype. Kamiishi et al. (2012) found that RNA interference mediating the suppression of the TrCHS1 gene expression may be closely related to the double-color formation of white flowers with purple splotches in Tricyrtis. Hosokawa et al. (2013) studied the P. hybrida cultivar Magic Samba, which showed an unstable double-color (red and white) phenotype under phosphorus (P)-deficiency stress, and found that the white region of the petals was mainly caused by the posttranscriptional silencing of the PhCHSA gene.
In contrast, interestingly, some studies have shown that virus infection can activate the expression of some pigment genes by inhibiting the RNA interference effect, resulting in the formation of double-color flowers (Senda et al., 2004; Shang et al., 2014). Teycheney and Tepfer (2001) studied the infection of the cultivar ‘Starmania’ with CMV-R virus in P. hybrida, and found that the virus can inhibit the RNA interference regulation of the PhCHS-A gene, resulting in the accumulation of pigments in the white area of the petals again.
DNA methylation.
Methylation mainly refers to the methylation of the promoter region, which usually occurs in the CpG island of the promoter and the first exon region. Cocciolone and Cone (1993) found that the methylation level of genomic DNA in heterozygous plants (Pl-Bh) of maize that showed the trait of variegated color was significantly higher than that in maize (Pl) plants with pure color, and considered that this variegated coloring pattern was caused by the difference in methylation degree. Qian et al. (2014) found that the double-color phenotype with red and green stripes in the bud mutation cultivar ‘Zaosuhong’ of pear was closely related to the methylation level difference in the promoter region of the PyMYB10 gene.
In terms of flower color in ornamental plants, Liu et al. (2012) studied two Oncidium orchid cultivars with or without color splotches and found that the methylation level of the OgCHS gene promoter region could directly affect the expression of the gene, resulting in the formation of the color splotches. Wang et al. (2019) isolated a differentially methylated fragment homologous to PsbHLH1 through methylation-sensitive amplified polymorphism (MSAP) analysis in P. suffruticosa ‘Shima Nishiki’, and further analysis suggested that it may be involved in the coloring difference of double-color flowers in this cultivar. Jiang et al. (2020) analyzed the difference in the methylation level and expression level of double-color (red and white) flowers in Prunus mume ‘Fuban Tiaozhi’, and considered that 13 genes (PmBAHD, PmCYP450, PmABC, etc.) with simultaneous differences in the preceding two levels may be involved in the flower color difference between red and white flowers. Wu et al. (2020) found that compared with the red flower bud, the leucoanthocyanidin dioxygenase (LDOX) promoter region has a higher methylation level in the double-color flower bud, which may be related to the color difference of the double-color flowers in peach ‘Sahong Tao’.
Conclusions and Perspectives
Double-color flowers in plants are a unique and attractive flower color phenotype that is relatively rare. This trait has higher ornamental, commercial, and breeding values (Zhao and Tao, 2015). Based on this, in recent years, the research on the coloring mechanism of double-color flowers has increasingly become a hotspot topic in the molecular biology field of ornamental plants.
With the rapid development of next-generation high-throughput sequencing technology, many researchers are studying the coloring molecular mechanism of double-color flowers in many ornamental plants based on sequencing technologies such as transcriptome, miRNA, proteome, and methylation. These plants mainly include peach (Chen et al., 2014), lotus (Deng et al., 2022), lily (Xu et al., 2017), herbaceous peony (Zhao et al., 2014, 2017a), tree peony (Zhang et al., 2018a, 2020, 2022), phalaenopsis (Zhao et al., 2019), pansy (Wang et al., 2022), and other ornamental plant species. Through these sequences, some key structural genes, TFs, miRNAs, and proteins that affect the coloring difference of double-color flowers can be screened at the gene and protein levels, and this can provide gene reserves for molecular breeding in the future.
Compared with the coloring mechanism of monochromatic flowers, that of double-color flowers is more complex (Fig. 3). In many plants, research on the molecular mechanism of double-color flowers is still in the initial stage of exploration. Although many results have been achieved, more in-depth gene function verification and detailed research of the molecular regulation network need to be further strengthened. With the completion of genome sequencing in more plant species with double-color flower phenotypes and the establishment of a stable transgenic verification system in their own species, as well as the in-depth development of various molecular biology and sequencing technologies and the emergence of new methods, it is believed that the molecular mechanism of coloring differences in double-color flowers in more plants will be revealed more objectively and accurately in the near future.
Analysis on model diagram of the coloring mechanisms of double-color flowers in plants. miRNA = micro RNA.
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
Analysis on model diagram of the coloring mechanisms of double-color flowers in plants. miRNA = micro RNA.
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
Analysis on model diagram of the coloring mechanisms of double-color flowers in plants. miRNA = micro RNA.
Citation: HortScience 57, 9; 10.21273/HORTSCI16723-22
For the breeding of double-color flowers in plants, we can comprehensively use a variety of breeding methods. Compared with traditional breeding methods, such as cross breeding and mutation breeding, more advanced genetic engineering technologies can be used for molecular breeding in the future, which will have greater advantages and potential and can accelerate the breeding process and more accurately cultivate new cultivars with excellent double-color flower traits.
Literature Cited
Albert, N.W., Davies, K.M., Lewis, D.H., Zhang, H.B., Montefiori, M., Brendolise, C., Boase, M.R., Ngo, H., Jameson, P.E. & Schwinn, K.E. 2014 A conserved network of transcriptional activators and repressors regulates anthocyanin pigmentation in eudicots Plant Cell 24 962 980 https://doi.org/10.1105/tpc.113.122069
Avila-Rostant, O., Lennon, A.M. & Umaharan, P. 2010 Spathe color variation in Anthurium andraeanum Hort. and its relationship to vacuolar pH HortScience 45 12 1768 1772 https://doi.org/10.21273/HORTSCI.45.12.1768
Baumann, K., Perez-Rodriguez, M., Bradley, D., Venail, J., Bailey, P., Jin, H.L., Koes, R., Roberts, K. & Martin, C. 2007 Control of cell and petal morphogenesis by R2R3 MYB transcription factors Development 134 1691 1701 https://doi.org/10.1242/dev.02836
Bonar, N., Liney, M., Zhang, R.X., Austin, C., Dessoly, J., Davidson, D., Stephens, J., McDougall, G., Taylor, M., Bryan, G.J. & Hornyik, C. 2018 Potato miR828 is associated with purple tuber skin and flesh color Front. Plant Sci. 9 1742 https://doi.org/10.3389/fpls.2018.01742
Cao, Y.W., Xu, L.F., Xu, H., Yang, P.P., He, G.R., Tang, Y.C., Qi, X.Y., Song, M. & Ming, J. 2021 LhGST is an anthocyanin-related glutathione S-transferase gene in Asiatic hybrid lilies (Lilium spp.) Plant Cell Rep. 40 85 95 https://doi.org/10.1007/s00299-020-02615-y
Chen, L., Liu, Y.S., Liu, H.D., Kang, L.M., Geng, J.M., Gai, Y.Z., Ding, Y.L., Sun, H.Y. & Li, Y.D. 2015 Identification and expression analysis of MATE genes involved in flavonoid transport in blueberry plants PLoS One 10 3 E0118578 https://doi.org/10.1371/journal.pone.0118578
Chen, Y.N., Mao, Y., Liu, H.L., Yu, F.X., Li, S.X. & Yin, T.M. 2014 Transcriptome analysis of differentially expressed genes relevant to variegation in peach flowers PLoS One 9 e90842 https://doi.org/10.1371/journal.pone.0090842
Chiou, C.Y. & Yeh, K.W. 2008 Differential expression of MYB gene (OgMYB1) determines color patterning in floral tissue of Oncidium Gower Ramsey Plant Mol. Biol. 66 379 388 https://doi.org/10.1007/s11103-007-9275-3
Chuck, G., Robbins, T., Nijjar, C., Ralston, E.D., Courtney-Gutterson, N. & Dooner, H.K. 1993 Tagging and cloning of a petunia flower color gene with the maize transposable element activator Plant Cell 5 371 378 https://doi.org/10.1105/tpc.5.4.371
Cocciolone, S.M. & Cone, K.C. 1993 Pl-Bh, an anthocyanin regulatory gene of maize that leads to variegated pigmentation Genetics 135 575 588 https://doi.org/10.1093/genetics/135.2.575
Davies, K.M., Albert, N.W. & Schwinn, K.E. 2012 From landing lights to mimicry: The molecular regulation of flower colouration and mechanisms for pigmentation patterning Funct. Plant Biol. 39 619 638 https://doi.org/10.1071/FP12195
Deng, J., Su, M.Y., Liu, X.L., Ou, K.F., Hu, Z.R. & Yang, P.F. 2022 Transcriptome analysis revealed the formation mechanism of floral color of lotus ‘Dasajin’ with bicolor petal Yuan Yi Xue Bao 49 365 377 https://doi.org/10.16420/j.issn.0513-353x.2021-0574
Duan, Y.J. & Cai, H. 1998 Study on variegated flowers Acta Phytopathologica Sin. 28 85 89
Dubos, C., Stracke, R., Grotewold, E., Weisshaar, B., Martin, C. & Lepiniec, L. 2010 MYB transcription factors in Arabidopsis Trends Plant Sci. 15 573 581 https://doi.org/10.1016/j.tplants.2010.06.005
Gani, U., Nautiyal, A.K., Kundan, M., Rout, B., Pandey, A. & Misra, P. 2022 Two homeologous MATE transporter genes, NtMATE21 and NtMATE22, are involved in the modulation of plant growth and flavonol transport in Nicotiana tabacum J. Exp. Bot. erac249 https://doi.org/10.1093/jxb/erac249
Gao, L.X., Yang, H.X., Liu, H.F., Yang, J. & Hu, Y.H. 2016a Extensive transcriptome changes underlying the flower color intensity variation in Paeonia ostii Front. Plant Sci. 6 1205 https://doi.org/10.3389/fpls.2015.01205
Gao, Z.Y., Xie, H.X., Liu, N.N. & Liu, S.L. 2016b Structural characteristics and function of mutator in maize Yumi Kexue 24 47 50
Gomez, C., Terrier, N., Torregrosa, L., Vialet, S., Fournier-Level, A., Verriès, C., Souquet, J.M., Mazauric, J.P., Klein, M., Cheynier, V. & Ageorges, A. 2009 Grapevine MATE-type proteins act as vacuolar H+-dependent acylated anthocyanin transporters Plant Physiol. 150 1 402 415 https://doi.org/10.1104/pp.109.135624
Gou, J.Y., Felippes, F.F., Liu, C.J., Weigel, D. & Wang, J.W. 2011 Negative regulation of anthocyanin biosynthesis in Arabidopsis by a miR156-targeted SPL transcription factor Plant Cell 23 1512 1522 https://doi.org/10.1105/tpc.111.084525
Grotewold, E 2006 The genetics and biochemistry of floral pigments Annu. Rev. Plant Biol. 57 761 780 https://doi.org/10.1146/annurev.arplant.57.032905.105248
Han, L.L., Zhou, L., Zou, H.Z., Yuan, M. & Wang, Y. 2022 PsGSTF3, an anthocyanin-related glutathione S-transferase gene, is essential for petal coloration in tree peony Int. J. Mol. Sci. 23 1423 https://doi.org/10.3390/ijms23031423
Han, Y.P., Vimolmangkang, S., Soria-Guerra, R.E. & Korban, S.S. 2012 Introduction of apple ANR genes into tobacco inhibits expression of both CHI and DFR genes in flowers, leading to loss of anthocyanin J. Expt. Bot. 63 2437 2447 https://doi.org/10.1093/jxb/err415
Hichri, I., Barrieu, F., Bogs, J., Kappel, C., Delrot, S. & Lauvergeat, V. 2011 Recent advances in the transcriptional regulation of the flavonoid biosynthetic pathway J. Expt. Bot. 62 2465 2483 https://doi.org/10.1093/jxb/erq442
Hosokawa, M., Yamauchi, T., Takahama, M., Goto, M., Mikano, S., Yamaguchi, Y., Tanaka, Y., Ohno, S., Koeda, S., Doi, M. & Yazawa, S. 2013 Phosphorus starvation induces post-transcriptional CHS gene silencing in Petunia corolla Plant Cell Rep. 32 601 609 https://doi.org/10.1007/s00299-013-1391-8
Hsu, C.C., Chen, Y.Y., Tsai, W.C., Chen, W.H. & Chen, H.H. 2015 Three R2R3-MYB transcription factors regulate distinct floral pigmentation patterning in Phalaenopsis spp Plant Physiol. 168 175 191 https://doi.org/10.1104/pp.114.254599
Hunter, D.A., Fletcher, J.D., Davies, K.M. & Zhang, H. 2011 Colour break in reverse bicolour daffodils is associated with the presence of Narcissus mosaic virus Virol. J. 8 412 https://doi.org/10.1186/1743-422X-8-412
Itoh, Y., Higeta, D., Suzuki, A., Yoshida, H. & Ozeki, Y. 2002 Excision of transposable elements from the chalcone isomerase and dihydroflavonol 4-reductase genes may contribute to the variegation of the yellow-flowered carnation (Dianthus caryophyllus) Plant Cell Physiol. 43 578 585 https://doi.org/10.1093/pcp/pcf065
Jiang, L.B., Zhang, M. & Ma, K.F. 2020 Whole-genome DNA methylation associated with differentially eExpressed genes regulated anthocyanin biosynthesis within flower color chimera of ornamental tree Prunus mume Forests 11 1 90 https://doi.org/10.3390/f11010090
Kamiishi, Y., Otani, M., Takagi, H., Han, D.S., Mori, S., Tatsuzawa, F., Okuhara, H., Kobayashi, H. & Nakano, M. 2012 Flower color alteration in the liliaceous ornamental Tricyrtis sp. by RNA interference-mediated suppression of the chalcone synthase gene Mol. Breed. 30 671 680 https://doi.org/10.1007/s11032-011-9653-z
Lalusin, A.G., Ohta, M. & Fujimura, T. 2006 Temporal and spatial expression of genes involved in anthocyanin biosynthesis during sweet potato (Ipomoea batatas [L.] Lam.) root development Int. J. Plant Sci. 167 249 256 https://doi.org/10.1086/499541
Li, M.T., Yu, L.J., Wang, L.M., Liu, J.M. & Lei, C. 2005 The heredity of flower colors and the discovery of flower color chimera in chrysanthemum species Hereditas 27 6 948 952
Li, H.H., Liu, X., An, J.P., Hao, Y.J., Wang, X.F. & You, C.X. 2017 Cloning and elucidation of the functional role of apple MdLBD13 in anthocyanin biosynthesis and nitrate assimilation. Plant Cell Tiss Org. 130 47 59 https://doi.org/10.1007/s11240-017-1203-x
Li, M.Y. & He, Y.X. 2005 Plant chimeras and application in the breeding of the ornamental plant Zhiwuxue Tongbao 22 6 641 647
Li, Y.K., Cui, W., Qi, X., Lin, M.M., Qiao, C.K., Zhong, Y.P., Hu, C.G. & Fang, J.B. 2020 MicroRNA858 negatively regulates anthocyanin biosynthesis by repressing AaMYBC1 expression in kiwifruit (Actinidia arguta) Plant Sci. 296 110476 https://doi.org/10.1016/j.plantsci.2020.110476
Li, Y.L., Xiong, X.Y., Yu, X.Y., He, C.Z., Lv, C.P., Yuan, F.R. & Zhu, J.H. 2010 Biological characteristics of variegated bud sports of Loropetalum chinense var. rubrum Linye Kexue 46 56 61
Liu, C.M. & Zhang, X. 2009 AFLP and SCAR markers analysis on the dual color flower mutants of Gladiolus. Acta Agr. Bor-Occid Sin. 18 237 240
Liu, D., Galli, M. & Crawford, N.M. 2001 Engineering variegated floral patterns in tobacco plants using the Arabidopsis transposable elements Tag1 Plant Cell Physiol. 42 4 419 423 https://doi.org/10.1093/pcp/pce053
Liu, X.J., Chuang, Y.N., Chiou, C.Y., Chin, D.C., Shen, F.Q. & Yeh, K.W. 2012 Methylation effect on chalcone synthase gene expression determines anthocyanin pigmentation in floral tissues of two Oncidium orchid cultivars Planta 236 401 409 https://doi.org/10.1007/s00425-012-1616-z
Luan, Y.T., Tang, Y.H., Wang, X., Xu, C., Tao, J. & Zhao, D.Q. 2022 Tree peony R2R3-MYB transcription factor PsMYB30 promotes petal blotch formation by activating the transcription of anthocyanin synthase Gene Plant Cell Physiol. pcac085 https://doi.org/10.1093/pcp/pcac085
Luo, X.N., Luo, S., Fu, Y.Q., Kong, C., Wang, K., Sun, D.Y., Li, M.C., Yan, Z.G., Shi, Q.Q. & Zhang, Y.L. 2022 Genome-wide identification and comparative profiling of microRNAs reveal flavonoid biosynthesis in two contrasting flower color cultivars of tree peony Front. Plant Sci. 12 797799 https://doi.org/10.3389/fpls.2021.797799
Martins, T.R., Berg, J.J., Blinka, S., Rausher, M.D. & Baum, D.A. 2013 Precise spatio-temporal regulation of the anthocyanin biosynthetic pathway leads to petal spot formation in Clarkia gracilis (Onagraceae) New Phytol. 197 958 969 https://doi.org/10.1111/nph.12062
McClintock, B 1948 Mutable loci in maize Carnegie Inst. Wash. Year Book 47 155 169
Morita, Y., Saito, R., Ban, Y., Tanikawa, N., Kuchitsu, K., Ando, T., Yoshikawa, M., Habu, Y., Ozeki, Y. & Nakayama, M. 2012 Tandemly arranged chalcone synthase A genes contribute to the spatially regulated expression of siRNA and the natural bicolor floral phenotype in Petunia hybrida Plant J. 70 5 739 749 https://doi.org/10.1111/j.1365-313X.2012.04908.x
Nakatsuka, T., Nishihara, M., Mishiba, K. & Yamamura, S. 2005 Temporal expression of favonoid biosynthesis-related genes regulates fower pigmentation in gentian plants Plant Sci. 168 5 1309 1318 https://doi.org/10.1016/j.plantsci.2005.01.009
Nishihara, M. & Nakatsuka, T. 2011 Genetic engineering of flavonoid pigments to modify flower color in floricultural plants Biotechnol. Lett. 33 433 441 https://doi.org/10.1007/s10529-010-0461-z
Nishijima, T., Morita, Y., Sasaki, K., Nakayama, M., Yamaguchi, H., Ohtsubo, N., Niki, T. & Niki, T. 2013 A torenia (Torenia fournieri Lind. ex Fourn.) novel mutant ‘flecked’ produces variegated flowers by insertion of a DNA transposon into an R2R3-MYB gene J. Jpn. Soc. Hort. Sci. 82 1 39 50 https://doi.org/10.2503/jjshs1.82.39
Noda, K., Glover, B.J., Linstead, P. & Martin, C. 1994 Flower color intensity depends on specialized cell-shape controlled by a Myb-related transcription factor Nature 369 661 664 https://doi.org/10.1038/369661a0
Noman, A., Aqeel, M., Deng, J.M., Khalid, N., Sanaullah, T. & He, S.L. 2017 Biotechnological advancements for improving floral attributes in ornamental plants Front. Plant Sci. 8 530 https://doi.org/10.3389/fpls.2017.00530
Ohno, S., Hori, W., Hosokawa, M., Tatsuzawa, F. & Doi, M. 2018 Identification of flavonoids in leaves of a labile bicolor flowering dahlia (Dahlia variabilis) ‘Yuino’ J. Jpn. Soc. Hort. Sci. 87 1 140 148 https://doi.org/10.2503/hortj.OKD-099
Ohno, S., Hosokawa, M., Kojima, M., Kitamura, Y., Hoshino, A., Tatsuzawa, F., Doi, M. & Yazawa, S. 2011 Simultaneous post-transcriptional gene silencing of two different chalcone synthase genes resulting in pure white flowers in the octoploid dahlia Planta 234 945 958 https://doi.org/10.1007/s00425-011-1456-2
Pashkovskiy, P., Ryazansky, S., Kartashov, A., Voloshin, R., Khudyakova, A., Kosobryukhov, A.A., Kreslavski, V.D., Kuznetsov, Vl.V. & Allakhverdiev, S.I. 2021 Effect of red light on photosynthetic acclimation and the gene expression of certain light signalling components involved in the microRNA biogenesis in the extremophile Eutrema salsugineum J. Biotechnol. 325 35 42 https://doi.org/10.1016/j.jbiotec.2020.11.018
Qi, Y., Zhou, L., Han, L.L., Zou, H.Z., Miao, K. & Wang, Y. 2020 PsbHLH1, a novel transcription factor involved in regulating anthocyanin biosynthesis in tree peony (Paeonia suffruticosa) Plant Physiol. Biochem. 154 396 408 https://doi.org/10.1016/j.plaphy.2020.06.015
`Qian, M.J., Ni, J.B., Niu, Q.F., Bai, S.L., Bao, L., Li, J.Z., Sun, Y.W., Zhang, D. & Teng, Y.W. 2017 Response of miR156-SPL module during the red peel coloration of bagging-treated Chinese Sand Pear (Pyrus pyrifolia Nakai) Front. Physiol. 8 550 https://doi.org/10.3389/fphys.2017.00550
Qian, M.J., Sun, Y.W., Allan, A.C., Teng, Y.W. & Zhang, D. 2014 The red sport of ‘Zaosu’ pear and its red-striped pigmentation pattern are associated with demethylation of the PyMYB10 promoter Phytochemistry 107 16 23 https://doi.org/10.1016/j.phytochem.2014.08.001
Quattrocchio, F., Verweij, W., Kroon, A., Spelt, C., Mol, J. & Koes, R. 2006 PH4 of petunia is an R2R3 MYB protein that activates vacuolar acidification through interactions with basic-Helix-Loop-Helix transcription factors of the anthocyanin pathway Plant Cell 18 5 1274 1291 https://doi.org/10.1105/tpc.105.034041
Sasaki, N., Nishizaki, Y., Uchida, Y., Wakamatsu, E., Umemoto, N., Momose, M., Okamura, M., Yoshida, H., Yamaguchi, M., Nakayama, M., Ozeki, Y. & Itoh, Y. 2012 Identification of the glutathione S-transferase gene responsible for flower color intensity in carnations Plant Biotechnol. 29 3 223 227 https://doi.org/10.5511/plantbiotechnology.12.0120a
Sato, M., Kawabe, T., Hosokawa, M., Tatsuzawa, F. & Doi, M. 2011 Tissue culture-induced flower-color changes in Saintpaulia caused by excision of the transposon inserted in the flavonoid 3',5' hydroxylase (F3'5’H) promoter Plant Cell Rep. 30 929 939 https://doi.org/10.1007/s00299-011-1016-z
Schaart, J.G., Dubos, C., Romero De La Fuente, I., van Houwelingen, A.M.M.L., de Vos, R.C.H., Jonker, H.H., Xu, W.J., Routaboul, J.M., Lipinec, L. & Bovy, A.G. 2013 Identification and characterization of MYB-bHLH-WD40 regulatory complexes controlling proanthocyanidin biosynthesis in strawberry (Fragaria × ananassa) fruits New Phytol. 197 2 454 467 https://doi.org/10.1111/nph.12017
Schreiber, H.D., Jones, A.H., Lariviere, C.M., Mayhew, K.M. & Cain, J.B. 2011 Role of aluminum in red-to-blue color changes in Hydrangea macrophylla sepals Biometals 24 1005 1015 https://doi.org/10.1007/s10534-011-9458-x
Senda, M., Masuta, C., Ohnishi, S., Goto, K., Kasai, A., Sano, T., Hong, J.S. & MacFarlane, S. 2004 Patterning of virus-infected Glycine max seed coat is associated with suppression of endogenous silencing of chalcone synthase genes Plant Cell 16 4 807 818 https://doi.org/10.1105/tpc.019885
Shang, X., Wang, J., Li, Q., Gong, S., Sun, H.Y. & Zhang, X.B. 2014 Research advance in the molecular mechanisms of plant flower blotch formation Yuan Yi Xue Bao 41 7 1485 1494
Shi, S.G., Yang, M., Zhang, M., Wang, P., Kang, Y.X. & Liu, J.J. 2014 Genome-wide transcriptome analysis of genes involved in flavonoid biosynthesis between red and white strains of Magnolia sprengeri pamp BMC Genomics 15 706 https://doi.org/10.1186/1471-2164-15-706
Shoji, K., Momonoi, K. & Tsuji, T. 2010 Alternative expression of vacuolar iron transporter and ferritin genes leads to blue/purple coloration of flowers in Tulip cv. ‘Murasakizuisho’ Plant Cell Physiol. 51 2 215 224 https://doi.org/10.1093/pcp/pcp181
Song, W. & Zhu, P.F. 2010 Study on mutation of chrysanthemum by ion implantation and separation of chimera. Nor Horticul. 3 135 138
Suzuki, K., Suzuki, T., Nakatsuka, T., Dohra, H., Yamagishi, M., Matsuyama, K. & Matsuura, H. 2016 RNA-seq-based evaluation of bicolor tepal pigmentation in Asiatic hybrid lilies (Lilium spp.) BMC Genomics 17 611 https://doi.org/10.1186/s12864-016-2995-5
Suzuki, M., Miyahara, T., Tokumoto, H., Hakamatsuka, T., Goda, Y., Ozeki, Y. & Sasaki, N. 2014 Transposon-mediated mutation of CYP76AD3 affects betalain synthesis and produces variegated flowers in four o’clock (Mirabilis jalapa) J. Plant Physiol. 171 17 1586 1590 https://doi.org/10.1016/j.jplph.2014.07.010
Takahashi, R., Morita, Y., Nakayama, M., Kanazawa, A. & Abe, J. 2012 An active CACTA-family transposable element is responsible for flower variegation in wild soybean Glycine soja Plant Genome 5 2 62 70 https://doi.org/10.3835/plantgenome2011.11.0028
Tanaka, Y., Nakamura, N. & Togami, J. 2008 Altering flower color in transgenic plants by RNAi-mediated engineering of flavonoid biosynthetic pathway Methods Mol. Biol. 442 245 257 https://doi.org/10.1007/978-1-59745-191-8_17
Tao, X.R., Qian, Y.J. & Zhou, X.P. 2006 Study on improvement of satellite DNA silencing vector and its effect on leaf color and flower color of Petunia hybrida Sci. Bull. (Beijing) 51 2041 2044
Teycheney, P.Y. & Tepfer, M. 2001 Virus-specific spatial differences in the interference with silencing of the chs-A gene in non-transgenic petunia J. Gen. Virol. 82 5 1239 1243 https://doi.org/10.1099/0022-1317-82-5-1239
Tirumalai, V., Swetha, C., Nair, A., Pandit, A. & Shivaprasad, P.V. 2019 miR828 and miR858 regulate VvMYB114 to promote anthocyanin and flavonol accumulation in grapes J. Expt. Bot. 70 18 4775 4792 https://doi.org/10.1093/jxb/erz264
Wang, L.R., Zhu, G.R. & Fang, W.C. 2012 Genetic resources of peach in China China Agricultural Press Beijing
Wang, T.X., Li, J., Li, T.G., Zhao, Y., Zhou, Y., Shi, Y.H., Peng, T., Song, X.Q., Zhu, Z.X. & Wang, J. 2022 Comparative transcriptome analysis of anthocyanin biosynthesis in pansy (Viola × wittrockiana Gams.) Agronomy (Basel) 12 4 919 https://doi.org/10.3390/agronomy12040919
Wang, Y., Zhao, M.Y., Xu, Z.D., Qi, S., Yu, X.Y. & Han, X. 2019 MSAP analysis of epigenetic changes reveals the mechanism of bicolor petal formation in Paeonia suffruticosa ‘Shima Nishiki’ 3 Biotech 9 313 https://doi.org/10.1007/s13205-019-1844-z
Wang, Y.X., Zhou, L.J., Wang, Y.G., Liu, S.H., Geng, Z.Q., Song, A.P., Jiang, J.F., Chen, S.M. & Chen, F.D. 2021 Functional identification of a flavone synthase and a flavonol synthase genes affecting flower color formation in Chrysanthemum morifolium Plant Physiol. Biochem. 166 1109 1120 https://doi.org/10.1016/j.plaphy.2021.07.019
Wu, Q., Zhang, H.J., Tian, J., Wang, X.H., Zhang, L. & Wang, L.S. 2018 A new cultivar of waterlily ‘Fen Ma Nao’ Yuan Yi Xue Bao 45 2807 2808 https://doi.org/10.16420/j.issn.0513-353x.2018-0443
Wu, X.X., Zhou, Y., Yao, D., Iqbal, S., Gao, Z.H. & Zhang, Z. 2020 DNA methylation of LDOX gene contributes to the floral colour variegation in peach J. Plant Physiol. 246-247 153116 https://doi.org/10.1016/j.jplph.2020.153116
Wu, Y.Q., Wei, M.R., Zhao, D.Q. & Tao, J. 2016 Flavonoid content and expression analysis of flavonoid biosynthetic genes in herbaceous peony (Paeonia lactiflora Pall.) with double colors J. Integr. Agric. 15 9 2023 2031 https://doi.org/10.1016/S2095-3119(15)61318-1
Xu, L.F., Yang, P.P., Feng, Y.Y., Xu, H., Cao, Y.W., Tang, Y.C., Yuan, S.X., Liu, X.Y. & Ming, J. 2017 Spatiotemporal transcriptome analysis provides insights into bicolor tepal development in Lilium “Tiny Padhye” Front. Plant Sci. 8 398 https://doi.org/10.3389/fpls.2017.00398
Yamagishi, M 2020 White with partially pink flower color in Lilium cernuum var. album is caused by transcriptional regulation of anthocyanin biosynthesis genes Scientia Hort. 260 108880 https://doi.org/10.1016/j.scienta.2019.108880
Yamagishi, M. & Sakai, M. 2020 The microRNA828/MYB12 module mediates bicolor pattern development in Asiatic hybrid lily (Lilium spp.) flowers Front. Plant Sci. 11 590791 https://doi.org/10.3389/fpls.2020.590791
Yin, P., Zhen, Y. & Li, S.X. 2019 Identification and functional classification of differentially expressed proteins and insight into regulatory mechanism about flower color variegation in peach Acta Physiol. Plant. 41 95 https://doi.org/10.1007/s11738-019-2886-x
Yoshida, K., Mori, M. & Kondo, T. 2009 Blue flower color development by anthocyanins: From chemical structure to cell physiology Nat. Prod. Rep. 26 884 915 https://doi.org/10.1039/B800165K
Yoshida, K., Kawachi, M., Mori, M., Maeshima, M., Kondo, M., Nishimura, M. & Kondo, T. 2005 The involvement of tonoplast proton pumps and Na+(K+)/H+ exchangers in the change of petal color during flower opening of morning glory, Ipomoea tricolor cv. Heavenly Blue Plant Cell Physiol. 46 3 407 415 https://doi.org/10.1093/pcp/pci057
Zhang, C., Fu, J.X., Wang, Y.J., Gao, S.L., Du, D.N., Wu, F., Guo, J. & Dong, L. 2015 Glucose supply improves petal coloration and anthocyanin biosynthesis in Paeonia suffruticosa ‘Luoyang Hong’ cut flowers Postharvest Biol. Technol. 101 73 81 https://doi.org/10.1016/j.postharvbio.2014.11.009
Zhang, G.T., Qi, H., Yang, S.N., Chu, Z.Y., Tian, T., Yuan, S.X. & Liu, C. 2021 Research progress of floral organ vacuole pH regulating flower color formation Biotechnol. Bull. 37 4 204 210 https://doi.org/10.13560/j.cnki.biotech.bull.1985.2020-0615
Zhang, R.J. & Lu, Y.Q. 2016 Molecular mechanisms and natural selection of flower color variation Bot. Res. 5 6 186 209 https://doi.org/10.12677/br.2016.56024
Zhang, X.P., Jia, J.S., Zhao, M.Y., Li, C., Han, X. & Xu, Z.D. 2022 Identification and characterization of microRNAs involved in double-color formation in Paeonia suffruticosa ‘Shima Nishiki’ by high-throughput sequencing Hortic. Environ. Biotechnol. 63 125 135 https://doi.org/10.1007/s13580-021-00379-2
Zhang, X.P., Xu, Z.D., Yu, X.Y., Zhao, L.Y., Zhao, M.Y., Han, X. & Qi, S. 2019 Identification of two novel R2R3-MYB transcription factors, PsMYB114L and PsMYB12L, related to anthocyanin biosynthesis in Paeonia suffruticosa Int. J. Mol. Sci. 20 5 1055 https://doi.org/10.3390/ijms20051055
Zhang, X.P., Zhao, L.Y., Xu, Z.D. & Yu, X.Y. 2018a Transcriptome sequencing of Paeonia suffruticosa ‘Shima Nishiki’ to identify differentially expressed genes mediating double-color formation Plant Physiol. Biochem. 123 114 124 https://doi.org/10.1016/j.plaphy.2017.12.009
Zhang, X.P., Zhao, M.Y., Guo, J., Zhao, L.Y. & Xu, Z.D. 2018b Anatomical and biochemical analyses reveal the mechanism of double-color formation in Paeonia suffruticosa ‘Shima Nishiki’ 3 Biotech 8 420 https://doi.org/10.1007/s13205-018-1459-9
Zhang, Y.Z., Cheng, Y.W., Xu, S.Z., Ma, H.P., Han, J.M. & Zhang, Y. 2020 Tree peony variegated flowers show a small insertion in the F3'H gene of the acyanic flower parts BMC Plant Biol. 20 211 https://doi.org/10.1186/s12870-020-02428-x
Zhao, A.J., Cui, Z., Li, T.G., Pei, H.Q., Sheng, Y.H., Li, X.Q., Zhao, Y., Zhou, Y., Huang, W.J., Song, X.Q., Peng, T. & Wang, J. 2019 mRNA and miRNA expression analysis reveal the regulation for flower spot patterning in Phalaenopsis ‘Panda’ Int. J. Mol. Sci. 20 17 4250 https://doi.org/10.3390/ijms20174250
Zhao, D.Q., Jiang, Y., Ning, C.L., Meng, J.S., Lin, S.S., Ding, W. & Tao, J. 2014 Transcriptome sequencing of a chimaera reveals coordinated expression of anthocyanin biosynthetic genes mediating yellow formation in herbaceous peony (Paeonia lactiflora Pall.) BMC Genomics 15 689 https://doi.org/10.1186/1471-2164-15-689
Zhao, D.Q. & Tao, J. 2015 Recent advances on the development and regulation of flower color in ornamental plants Front. Plant Sci. 6 261 https://doi.org/10.3389/fpls.2015.00261
Zhao, D.Q., Tao, J., Han, C.X. & Ge, J.T. 2012 Flower color diversity revealed by differential expression of flavonoid biosynthetic genes and flavonoid accumulation in herbaceous peony (Paeonia lactiflora Pall.) Mol. Biol. Rep. 39 11263 11275 https://doi.org/10.1007/s11033-012-2036-7
Zhao, D.Q., Wei, M.R., Shi, M., Hao, Z.J. & Tao, J. 2017a Identification and comparative profiling of miRNAs in herbaceous peony (Paeonia lactiflora Pall.) with red/yellow bicoloured flowers Sci. Rep. 7 44926 https://doi.org/10.1038/srep44926
Zhao, D.Q., Xia, X., Wei, M.R., Sun, J., Meng, J.S. & Tao, J. 2017b Overexpression of herbaceous peony miR156e-3p improves anthocyanin accumulation in transgenic Arabidopsis thaliana lateral branches 3 Biotech 7 379 https://doi.org/10.1007/s13205-017-1011-3
Zhao, R.L. & Zhang, D.X. 1992 Preliminary study on isolation of chrysanthemum chimera by tissue culture Liaoning Agric. Sci. 4 56 57
Zheng, Y.J., Li, T., Liu, H.T., Pan, Q.H., Zhan, J.C. & Huang, W.D. 2009 Sugars induce anthocyanin accumulation and flavanone 3-hydroxylase expression in grape berries Plant Growth Regulat. 58 251 260 https://doi.org/10.1007/s10725-009-9373-0
