Cloning of cDNA coding for dihydroflavonol-4-reductase (DFR) and characterization of dfr expression in the corollas of Gerbera hybrida var. Regina (Compositae)

Identification of key genes responsible for green and white colored spathes in Anthurium andraeanum (Hort.)

Modern anthuriums, Anthurium andraeanum (Hort.) are among the most popular flowering plants and widely used for interior decoration. Their popularity is largely attributed to the exotic spathes with different colors. Previous studies have reported color development in red spathe cultivars, but limited information is available on key genes regulating white and green colored spathes. This study analyzed anthocyanin, chlorophyll, and carotenoid contents as well as transcript differences in spathes of eight cultivars that differed in spathe colors ranging from red to white and green. Results showed that increased expression of a transcription factor AaMYB2 was associated with elevated levels of anthocyanin in spathes, but decreased expression of AaMYB2 and increased expression of AaLAR (leucoanthocyanidin reductase) and AaANR (anthocyanidin reductase) were accompanied with the accumulation of colorless proanthocyanidin, thus the white spathe. As to the green colored spathe, chlorophyll content in the green spathe cultivar was substantially higher than the other cultivars. Correspondingly, transcripts of chlorophyll biosynthesis-related genes AaHemB (porphobilinogen synthase) and AaPor (protochlorophyllide oxidoreductase) were highly upregulated but almost undetectable in white and red spathes. The increased expression of AaHemB and AaPor was correlated with the expression of transcription factor AaMYB124. Subsequently, qRT-PCR analysis confirmed their expression levels in nine additional cultivars with red, white, and green spathes. A working model for the formation of white and green spathes was proposed. White colored spathes are likely due to the decreased expression of AaMYB2 which results in increased expression of AaLAR and AaANR, and the green spathes are attributed to AaMYB124 enhanced expression of AaHemB and AaPor. Further research is warranted to test this working model.

Reinterpretation of anthocyanins biosynthesis in developing black rice seeds through gene expression analysis

The biosynthesis of anthocyanins is still questionable in regulating the quantities of anthocyanins biosynthesized in rice seeds and the expression levels of transcription factors and the structural genes involved in the biosynthetic pathway of anthocyanins. We herein investigated the relationship between the accumulated anthocyanin contents and the expression levels of genes related to the biosynthesis of anthocyanins in rice seeds. Liquid chromatography/mass spectrometry-mass spectrometry analysis of cyanidin 3-glucoside (C3G) in rice seeds showed no accumulation of C3G in white and red rice cultivars, and the differential accumulation of C3G among black rice cultivars. RNA-seq analysis in rice seeds, including white, red, and black rice cultivars, at twenty days after heading (DAH) further exhibited that the genes involved in the biosynthesis of anthocyanins were differentially upregulated in developing seeds of black rice. We further verified these RNA-seq results through gene expression analysis by a quantitative real-time polymerase chain reaction in developing seeds of white, red, and black rice cultivars at 20 DAH. Of these genes related to the biosynthesis of anthocyanins, bHLHs, MYBs, and WD40, which are regulators, and the structural genes, including chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), flavonoid 3´-hydroxylase (F3´H), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS), were differentially upregulated in black rice seeds. The correlation analysis revealed that the quantities of C3G biosynthesized in black rice seeds were positively correlated to the expression levels of bHLHs, MYBs and WD40, CHS, F3H, F3´H, DFR, and ANS. In addition, we present bHLH2 (LOC_Os04g47040) and MYBs (LOC_Os01g49160, LOC_Os01g74410, and LOC_Os03g29614) as new putative transcription factor genes for the biosynthesis of anthocyanins in black rice seeds. It is expected that this study will help to improve the understanding of the molecular levels involved in the biosynthesis of anthocyanins in black rice seeds.

Integrated analysis of metabolome and transcriptome reveals key candidate genes involved in flavonoid biosynthesis in Pinellia ternata under heat stress

Pinellia ternata (Thunb.) Breit. is an important traditional Chinese medicinal herb and very sensitive to high temperatures. To gain a better understanding of flavonoid biosynthesis under heat stress in P. ternata, we performed integrated analyses of metabolome and transcriptome data. P. ternata plants were subjected to a temperature of 38 °C, and samples were collected after 10 d of treatment. A total of 502 differential accumulated metabolites and 5040 different expressed transcripts were identified, with flavonoid biosynthesis predominantly enriched. Integrated metabolomics and transcriptome analysis showed that high temperature treatment upregulated the expression of CYP73A and downregulated the expression of other genes (such as HCT, CCoAOMT, DFR1, DFR2), which might inhibit the biosynthesis of the downstream metabolome, including such metabolites as chlorogenic acid, pelargonidin, cyanidin, and (-)-epigallocatechin in the flavonoid biosynthesis pathway. The transcription expression levels of these genes were validated by real-time PCR. Our results provide valuable insights into flavonoid composition and accumulation patterns and the candidate genes participating in the flavonoid biosynthesis pathways under heat stress in P. ternata.

Blue Light Supplemented at Intervals in Long-Day Conditions Intervenes in Photoperiodic Flowering, Photosynthesis, and Antioxidant Properties in Chrysanthemums

The flowering of chrysanthemum (Chrysanthemum morifolium Ramat.), inhibited by long-day lighting, can be reversed with a short period of low supplemental blue light (S-BL). Both flowering and the reactive oxygen species (ROS) scavenging processes are primarily driven by sugars created by photosynthetic carbon assimilation. In addition, the antioxidant ability potentially affects flowering in photoperiod- and/or circadian rhythm-dependent manners. This indicates that there is an interactive relationship among blue (B) light, photosynthetic efficiency, sugar accumulation, and antioxidant ability in flowering regulation. Here, 4 h of 30 μmol·m-2·s-1 photosynthetic photon flux density (PPFD) S-BL was applied at the end of a 13-h long-day period (LD13 + 4B) at different intervals during 60 days of experimental duration. The five experimental groups were named according to the actual number of days of S-BL and their intervals: applied once every day, "60 days-(LD13 + 4B) (100.0%)"; once every other day, "30 days-(LD13 + 4B) (50.0%)"; once every three days, "15 days-(LD13 + 4B) (25.0%)"; once every five days, "10 days-(LD13 + 4B) (16.7%)"; and once every seven days, "7 days-(LD13 + 4B) (11.7%)". Two non-S-BL control groups were also included: 60 10-h short days (60 days-SD10) and 13-h long days (60 days-LD13). At the harvest stage, varying degrees of flowering were observed except in "60 days-LD13" and "7 days-(LD13 + 4B) (11.7%)". The number of flowers increased and the flower buds appeared earlier as the proportion of S-BL days increased in LD13 conditions, although the "60 days-SD10" gave the earliest flowering. The proportion of initial, pivotal, and optimal flowering was 16.7% ("10 days-(LD13 + 4B)"), 50.0% ("30 days-(LD13 + 4B)"), and 100.0% ("60 days-(LD13 + 4B)"), respectively. Meanwhile, a series of physiological parameters such as the production of enzymatic or non-enzymatic antioxidants, chlorophyll content, photosynthetic efficiency, enzyme activities, and carbohydrate accumulation were significantly improved by "30 days-(LD13 + 4B) (50.0%)" as a turning point until the peaks appeared in "60 days-(LD13 + 4B) (100.0%)", as well as the expression of florigenic or anti-florigenic and some antioxidant-synthetic genes. Furthermore, the results of principal component analysis (PCA) indicated that S-BL days positively regulated flowering, photosynthesis, carbohydrate accumulation, and antioxidant production. In aggregate, the pivotal and optimal proportions of S-BL days to reconcile the relationship among flowering, photosynthetic carbon assimilation, and antioxidant ability were 50.0% and 100.0%, respectively. However, there are still significant gaps to be filled in order to determine the specific involvement of blue light and antioxidant abilities in flowering regulation.

Polyketide reductases in defense-related parasorboside biosynthesis in Gerbera hybrida share processing strategies with microbial polyketide synthase systems

Plant polyketides are well-known for their crucial functions in plants and their importance in the context of human health. They are synthesized by type III polyketide synthases (PKSs) and their final functional diversity is determined by post-PKS tailoring enzymes. Gerbera hybrida is rich in two defense-related polyketides: gerberin and parasorboside. Their synthesis is known to be initiated by GERBERA 2-PYRONE SYNTHASE 1 (G2PS1), but the polyketide reductases (PKRs) that determine their final structure have not yet been identified. We identified two PKR candidates in the pathway, GERBERA REDUCTASE 1 (GRED1) and GRED2. Gene expression and metabolite analysis of different gerbera tissues, cultivars, and transgenic gerbera plants, and in vitro enzyme assays, were performed for functional characterization of the enzymes. GRED1 and GRED2 catalyze the second reduction step in parasorboside biosynthesis. They reduce the proximal keto domain of the linear CoA bound intermediate before lactonization. We identified a crucial tailoring step in an important gerbera PKS pathway and show that plant polyketide biosynthesis shares processing strategies with fungi and bacteria. The two tailoring enzymes are recruited from the ancient sporopollenin biosynthetic pathway to a defense-related PKS pathway in gerbera. Our data provide an example of how plants recruit conserved genes to new functions in secondary metabolism that are important for environmental adaptation.

A single-base insertion in BoDFR1 results in loss of anthocyanins in green-leaved ornamental kale

A CRISPR/Cas9-based knockout assay verified that BoDFR1 drives anthocyanin accumulation in ornamental kale and that BoDFR2, an ortholog of BoDFR1, is redundant. Anthocyanins are widely distributed in nature and give plants their brilliant colors. Leaf color is an important trait for ornamental kale. In this study, we measured anthocyanin contents and performed transcriptome deep sequencing (RNA-seq) of leaves from pink and green ornamental kale. We observed substantial differences in the expression levels of the two DIHYDROFLAVONOL 4-REDUCTASE-encoding genes BoDFR1 (Bo9g058630) and its ortholog BoDFR2 (Bo2g116380) between green-leaved and pink-leaved kale by RNA-seq and RT-qPCR. We cloned and sequenced BoDFR1 and BoDFR2 from both types of kale. We identified a 1-bp insertion in BoDFR1 and a 2-bp insertion in BoDFR2 in green-leaved kale compared to the sequences obtained from pink-leaved kale, both mapping to the second exon of their corresponding gene and leading to premature termination of translation. To confirm the genetic basis of the absence of anthocyanins in green kale, we used CRISPR/Cas9 genome editing to separately knock out BoDFR1 or BoDFR2 in the pink-leaved ornamental kale inbred line P23. We detected very low accumulation of anthocyanins in the resulting mutants Bodfr1-1 and Bodfr1-2, while Bodfr2-1 and Bodfr2-2 had anthocyanin levels comparable to those of the wild-type. We conclude that the insertion in BoDFR1, rather than that in BoDFR2, underlies the lack of anthocyanins in green-leaved ornamental kale. This work provides insight into the function of DFR and will contribute to germplasm improvement of ornamental plants.

Functional analysis of the dihydroflavonol 4-reductase family of Camellia sinensis: exploiting key amino acids to reconstruct reduction activity

Anthocyanins and proanthocyanidins (PAs) are important types of flavonoids, plant secondary metabolites with a wide range of industrial and pharmaceutical applications. DFR (dihydroflavonol 4-reductase) is a pivotal enzyme that plays an important role in the flavonoid pathway. Here, four CsDFR genes were isolated from Camellia sinensis, and their overexpression was analyzed in vitro and in vivo. Based on transcription and metabolic analyses, CsDFR expression was closely consistent with catechins and PAs accumulation. Moreover, enzyme activity analyses revealed that the two recombinant proteins CsDFRa and CsDFRc exhibited DFR activity, converting dihydroflavonols into leucoanthocyanins in vitro, but CsDFRb1 and CsDFRb3 did not. CsDFRa and CsDFRc overexpression in AtDFR mutants (tt3) revealed that CsDFRs are involved in the biosynthesis of anthocyanins and PAs, as CsDFRa and CsDFRc restored not only the purple petiole phenotype but also the seed coat color. Site-directed mutagenesis revealed that the two amino acid residues S117 and T123 of CsDFRa play a prominent role in controlling DFR reductase activity. Enzymatic assays indicated that CsDFRa and CsDFRc exhibited a higher affinity for DHQ and DHK, respectively, whereas CsDFRb1^N120S and CsDFRb1^C126T exhibited a higher affinity for DHM. Our findings comprehensively characterize the DFRs from C. sinensis and shed light on their critical role in metabolic engineering.

Biosynthesis and regulation of anthocyanin pathway genes

Anthocyanins are the phenolic compounds responsible for coloring pigments in fruits and vegetables. Anthocyanins offer a wide range of health benefits to human health. Their scope has expanded dramatically in the past decade, making anthocyanin control, influx, and outflow regulation fascinating for many researchers. The main culprit is anthocyanin stability and concentration form, which demands novel ways because these are critical in the food industry. This review aims to examine anthocyanin synthesis via triggering transcription genes that code for anthocyanin-producing enzymes. The balance between production and breakdown determines anthocyanin accumulation. Thus, increasing the anthocyanin content in food requires the stability of molecules in the vacuolar lumen, the pigment fading process, and a better understanding of the mechanism. The promising option is biosynthesis by metabolically engineered microorganisms with a lot of success. This study aims to look into and evaluate the existing literature on anthocyanin production, namely the biosynthesis of anthocyanin pathway genes, production by microbial cell factories, and the regulatory factors that can modulate the production of anthocyanins. Understanding these mechanisms will provide new biotechnological approaches.Key points• Factors affecting the regulation of anthocyanins• Focus on degradation, biosynthesis pathway genes, and alternative systems for the production of anthocyanins• Microbial cell factories can be used to produce large amounts of anthocyanins.

Functional Analysis of Genes GlaDFR1 and GlaDFR2 Encoding Dihydroflavonol 4-Reductase (DFR) in Gentiana lutea L. Var. Aurantiaca (M. Laínz) M. Laínz

Anthocyanins are important pigments for flower color, determining the ornamental and economic values of horticultural plants. As a key enzyme in the biosynthesis of anthocyanidins, dihydroflavonol 4-reductase (DFR) catalyzes the reduction of dihydroflavonols to generate the precursors for anthocyanidins (i.e., leucoanthocyanidins) and anthocyanins. To investigate the functions of DFRs in plants, we cloned the GlaDFR1 and GlaDFR2 genes from the petals of Gentiana lutea var. aurantiaca and transformed both genes into Nicotiana tabacum by Agrobacterium-mediated leaf disc method. We further investigated the molecular and phenotypic characteristics of T1 generation transgenic tobacco plants selected based on the hygromycin resistance and verified by both PCR and semiquantitative real-time PCR analyses. The phenotypic segregation was observed in the flower color of the transgenic tobacco plants, showing petals darker than those in the wild-type (WT) plants. Results of high-performance liquid chromatography (HPLC) analysis showed that the contents of gentiocyanin derivatives were decreased in the petals of transgenic plants in comparison to those of WT plants. Ours results revealed the molecular functions of GlaDFR1 and GlaDFR2 in the formation of coloration, providing solid theoretical foundation and candidate genes for further genetic improvement in flower color of plants.

Integrated Metabolomic and Transcriptomic Analysis Reveals Differential Mechanism of Flavonoid Biosynthesis in Two Cultivars of Angelica sinensis

Angelica sinensis is a traditional Chinese medicinal plant that has been primarily used as a blood tonic. It largely relies on its bioactive metabolites, which include ferulic acid, volatile oils, polysaccharides and flavonoids. In order to improve the yield and quality of A. sinensis, the two cultivars Mingui 1 (M1), with a purple stem, and Mingui 2 (M2), with a green stem, have been selected in the field. Although a higher root yield and ferulic acid content in M1 than M2 has been observed, the differences of flavonoid biosynthesis and stem-color formation are still limited. In this study, the contents of flavonoids and anthocyanins were determined by spectrophotometer, the differences of flavonoids and transcripts in M1 and M2 were conducted by metabolomic and transcriptomic analysis, and the expression level of candidate genes was validated by qRT-PCR. The results showed that the contents of flavonoids and anthocyanins were 1.5- and 2.6-fold greater in M1 than M2, respectively. A total of 26 differentially accumulated flavonoids (DAFs) with 19 up-regulated (UR) and seven down-regulated (DR) were obtained from the 131 identified flavonoids (e.g., flavonols, flavonoid, isoflavones, and anthocyanins) in M1 vs. M2. A total 2210 differentially expressed genes (DEGs) were obtained from the 34,528 full-length isoforms in M1 vs. M2, and 29 DEGs with 24 UR and 5 DR were identified to be involved in flavonoid biosynthesis, with 25 genes (e.g., CHS1, CHI3, F3H, DFR, ANS, CYPs and UGTs) mapped on the flavonoid biosynthetic pathway and four genes (e.g., RL1, RL6, MYB90 and MYB114) belonging to transcription factors. The differential accumulation level of flavonoids is coherent with the expression level of candidate genes. Finally, the network of DAFs regulated by DEGs was proposed. These findings will provide references for flavonoid production and cultivars selection of A. sinensis.

Functional analysis of a dihydroflavonol 4-reductase gene in Ophiorrhiza japonica (OjDFR1) reveals its role in the regulation of anthocyanin

Dihydroflavonol 4-reductase (DFR), a key regulatory enzyme, participated in the biosynthesis of anthocyanins, proanthocyanidins and other flavonoids that essential for plant survival and human health. However, the role of this enzyme in Ophiorrhiza japonica is still unknown. Here, three putative DFR-like genes were firstly isolated from O. japonica. Phylogenetic analysis indicated that OjDFR1 was classified into DFR subgroup, while the rest two were clustered into other NADPH-dependent reductases. Then, functions of the three genes were further characterized. Expression analysis showed that OjDFR1 transcripts had strong correlations with the accumulation pattern of anthocyanin during the flower developmental, whereas other two were not, this suggested the potential roles of OjDFR1 in anthocyanin biosynthesis. Subsequently, all three clones were functionally expressed in Escherichia coli, but confirming that only OjDFR1 encode active DFR proteins that catalyzed the reduction of dihydroflavonols to leucoanthocyanidin. Consistant with the biochemical assay results, overexpressing OjDFR1 in Arabidopsis tt3-1 mutant successfully restored the deficiency of anthocyanin and proanthocyanidin, hinting its function as DFR in planta. Additionally, heterologous expression of OjDFR1 in transgenic tobacco contributed to darker flower color via up-regulating the expressions of endogenous NtANS and NtUFGT, which suggested that OjDFR1 was involved in flower color development. In summary, this study validates the functions of OjDFR1 and expands our understanding of anthocyanin biosynthesis in O. japonica.

Tetraketide α-pyrone reductases in sporopollenin synthesis pathway in Gerbera hybrida: diversification of the minor function

The structurally robust biopolymer sporopollenin is the major constituent of the exine layer of pollen wall and plays a vital role in plant reproductive success. The sporopollenin precursors are synthesized through an ancient polyketide biosynthetic pathway consisting of a series of anther-specific enzymes that are widely present in all land plant lineages. Tetraketide α-pyrone reductase 1 (TKPR1) and TKPR2 are two reductases catalyzing the final reduction of the carbonyl group of the polyketide synthase-synthesized tetraketide intermediates to hydroxylated α-pyrone compounds, important precursors of sporopollenin. In contrast to the functional conservation of many sporopollenin biosynthesis associated genes confirmed in diverse plant species, TKPR2's role has been addressed only in Arabidopsis, where it plays a minor role in sporopollenin biosynthesis. We identified in gerbera two non-anther-specific orthologues of AtTKPR2, Gerbera reductase 1 (GRED1) and GRED2. Their dramatically expanded expression pattern implies involvement in pathways outside of the sporopollenin pathway. In this study, we show that GRED1 and GRED2 are still involved in sporopollenin biosynthesis with a similar secondary role as AtTKPR2 in Arabidopsis. We further show that this secondary role does not relate to the promoter of the gene, AtTKPR2 cannot rescue pollen development in Arabidopsis even when controlled by the AtTKPR1 promoter. We also identified the gerbera orthologue of AtTKPR1, GTKPR1, and characterized its crucial role in gerbera pollen development. GTKPR1 is the predominant TKPR in gerbera pollen wall formation, in contrast to the minor roles GRED1 and GRED2. GTKPR1 is in fact an excellent target for engineering male-sterile gerbera cultivars in horticultural plant breeding.

Beyond Purple Tomatoes: Combined Strategies Targeting Anthocyanins to Generate Crimson, Magenta, and Indigo Fruit

The range of colours of many flowers and fruits is largely due to variations in the types of anthocyanins produced. The degree of hydroxylation on the B-ring affects the hue of these pigments, causing a shift from the orange end of the visible spectrum to the blue end. Besides colour, this modification can also affect other properties of anthocyanins, including the ability to protect the plant against different stresses or, when included in the human diet, to provide benefits for disease prevention. The level of hydroxylation of the B-ring is determined by the activity of two key hydroxylases, F3′H and F3′5′H, and by the substrate preference of DFR, an enzyme acting downstream in the biosynthetic pathway. We show that, in tomato, a strategy based on fruit-specific engineering of three regulatory genes (AmDel, AmRos1, AtMYB12) and a single biosynthetic gene (AmDFR), together with the availability of a specific mutation (f3′5′h), results in the generation of three different varieties producing high levels of anthocyanins with different levels of hydroxylation. These tomatoes show distinctive colours and mimic the classes of anthocyanins found in natural berries, thus providing unique near-isogenic material for different studies.

Sepal Identity of the Pappus and Floral Organ Development in the Common Dandelion (Taraxacum officinale; Asteraceae)

The dry one-seeded fruits (cypselae) of the Asteraceae are often crowned with a pappus, an appendage of hairs or scales that assists in dispersal. It is generally assumed, but little investigated, that the pappus represents the outer floral whorl where the sepals are usually located. We analysed pappus–sepal homology in dandelions using micromorphological and floral gene expression analyses. We show that the pappus initiates from a ring primordium at the base of the corolla, heterochronic to the petals. Pappus parts form from this ring, with those in the alternipetalaous position usually being ahead in growth, referring to sepal identity. Tof-APETALLA1 expression increased during floret development and was highest in mature pappus. Tof-PISTILLATA expression was high and confined to the floral tissues containing the petals and stamens, consistent with expectations for sepals. Apart from the pappus, the dispersal structure of dandelion consists of the upper part of the fruit, the beak, which originates from the inner floral whorl. Thus, our results support the homology of the pappus with the sepals, but show that it is highly derived. Together with our floral stage definitions and verified qPCR reference genes, they provide a basis for evolution and development studies in dandelions and possibly other Asteraceae.

Fine mapping of a kernel length-related gene with potential value for maize breeding

A key candidate gene for maize kernel length was fine mapped to an interval of 942 kb; the locus significantly increases kernel length (KL) and hundred-kernel weight (HKW). Kernel size is a major determinant of yield in cereals. Kernel length, one of the determining factors of kernel size, is a target trait for both domestication and artificial breeding. However, there are few reports of fine mapping and quantitative trait loci (QTLs)/cloned genes for kernel length in maize. In this project, a novel major QTL, named qKL9, controlling maize kernel length was identified. We verified the authenticity and stability of qKL9 via BC₂F₂ and BC₃F₁ populations, respectively, and ultimately mapped qKL9 to an ~ 942-kb genomic interval by testing the progenies of recombination events derived from BC₃F₂ and BC₄F₂ populations in multiple environments. Additionally, one new line (Mc^qKL9-A) containing the ~ 942-kb segment was screened from the BC₄F₂ population. Combining transcriptome analysis between Mc^qKL9-A and Mc at 6, 9 and 14 days after pollination and candidate regional association mapping, Zm00001d046723 was preliminarily identified as the key candidate gene for qKL9. Importantly, the replacement in the Mc line of the Mc's alleles by the V671's alleles in the qKL9 region improved the performances of single-cross hybrids obtained with elite lines, illustrating the potential value of this QTL for the genetic improvement in maize kernel-related traits. These findings facilitate molecular breeding for kernel size and cloning of the gene underlying qKL9, shedding light on the genetic basis of kernel size in maize.

A Roadmap to Modulated Anthocyanin Compositions in Carrots

Anthocyanins extracted from black carrots have received increased interest as natural colorants in recent years. The reason is mainly their high content of acylated anthocyanins that stabilizes the color and thereby increases the shelf-life of products colored with black carrot anthocyanins. Still, the main type of anthocyanins synthesized in all black carrot cultivars is cyanidin limiting their use as colorants due to the narrow color variation. Additionally, in order to be competitive against synthetic colors, a higher percentage of acylated anthocyanins and an increased anthocyanin content in black carrots are needed. However, along with the increased interest in black carrots there has also been an interest in identifying the structural and regulatory genes associated with anthocyanin biosynthesis in black carrots. Thus, huge progress in the identification of genes involved in anthocyanin biosynthesis has recently been achieved. Given this information it is now possible to attempt to modulate anthocyanin compositions in black carrots through genetic modifications. In this review we look into genetic modification opportunities for generating taproots of black carrots with extended color palettes, with a higher percentage of acylated anthocyanins or a higher total content of anthocyanins.

Anthocyanin Genes Involved in the Flower Coloration Mechanisms of Cymbidium kanran

The Orchidaceae, otherwise known as orchids, is one of the largest plant families and is renowned for its spectacular flowers and ecological adaptations. Various polymorphisms of orchid flower colour can attract pollinators and be recognised as valuable horticultural ornamentals. As one of the longest historic cultured orchids, Cymbidium kanran has been domesticated for more than 2,500 years and is an ideal species to study coloration mechanisms because of plentiful variations in floral coloration and abundant traditional varieties. In this study, we used two distinct colour-type flowers of C. kanran as experimental materials to elucidate the mechanism of flower coloration. High-performance liquid chromatography (HPLC) analysis revealed that anthocyanins in purple-red-type flowers include three types of anthocyanidin aglycones, peonidin, malvidin, and cyanidin, whereas anthocyanins are lacking in white-type flowers. Through comparative transcriptome sequencing, 102 candidate genes were identified as putative homologues of colour-related genes. Based on comprehensive correlation analysis between colour-related compounds and gene expression profiles, four candidates from 102 captured genes showed a positive correlation with anthocyanidin biosynthesis. Furthermore, transient expression of CkCHS-1, CkDFR, and CkANS by particle bombardment confirmed that recovery of their expression completed the anthocyanin pathway and produced anthocyanin compounds in white-type flowers. Collectively, this study provided a comprehensive transcriptomic dataset for Cymbidium, which significantly facilitate our understanding of the molecular mechanisms of regulating floral pigment accumulation in orchids.

Event-specific qualitative polymerase chain reaction analysis for two T-DNA copies in genetically modified orange Petunia

In 2017, various orange coloured petunia on the market turned out to be genetically modified (GM) without an official authorization for commercialization. Sequence analysis suggested these undeclared plants most probably originated from a plant transformation experiment performed in the 1980s. For a deeper understanding how GM petunia entered classical breeding programmes worldwide, and whether they originated from a single source or not, we undertook a molecular genetic characterization of the T-DNA integration sites in different GM petunia cultivars and breeding lines. By means of genome walking, we isolated different T-DNA sequences, which are located at the junctions between the T-DNA(s) and the petunia DNA. Based on the results obtained we conclude that there are at least two T-DNA copies of different lengths. This is supported by Southern blot analysis. For T-DNA1, the 3'-junction sequence was isolated, whereas the 5'-junction remained unclear. In contrast, for T-DNA2, the 5'-junction sequence was isolated, whereas the sequence isolated from the 3'-region consists only of T-DNA, but did not include the junction from the T-DNA to the petunia DNA. We developed primers for event-specific PCRs and screened a set of three orange GM petunia cultivars and 126 GM offspring from a commercial breeding program. We show that both T-DNA copies are present in all our tested GM petunia samples, which underpins the assumption of a single transgenic origin of the undeclared GM petunia. Most likely, the two T-DNAs are integrated in close proximity into the petunia genome.

Differential expression of anthocyanin structural genes and transcription factors determines coloration patterns in gerbera flowers

We investigated the expression of anthocyanin structural genes and transcription factors (TFs) associated with varying anthocyanin content during different developmental stages (S1-S4) of the gerbera cultivars 'Nathasha' and 'Rosalin'. Accumulation of anthocyanin started at S1 and reached a maximum at S3 in both cultivars. Enhancement of anthocyanin content in 'Nathasha' was associated with upregulation of ANS and MYB10, whereas in 'Rosalin', upregulation was associated with CHS1, MYB10, and MYC1. Low-temperature exposure (6 °C) enhanced anthocyanin content to a greater extent than that at 22 °C via stronger upregulation of CHS1 and MYB10 in 'Nathasha' and CHS1 in 'Rosalin', irrespective of flower developmental stage. However, differences in anthocyanin content between the two cultivars were found to be influenced by the expression levels of all structural genes and TFs, irrespective of flower developmental stage and temperature conditions. We suggest that differences in the regulation mechanisms of anthocyanin biosynthesis and coloration pattern between 'Nathasha' and 'Rosalin' are related to differences in the expression patterns of structural genes and TFs; however, further functional studies of the key genes in anthocyanin biosynthesis are needed.

Scandinavian perspectives on plant gene technology: applications, policies and progress

Plant research and breeding has a long and successful history in the Scandinavian countries, Denmark, Finland, Norway and Sweden. Researchers in the region have been early in adopting plant gene technologies as they developed. This review gives a background, as well as discuss the current and future progress of plant gene technology in these four countries. Country-specific details of the regulation of genetically modified plants are described, as well as similarities and differences in the approach to regulation of novel genome-editing techniques. Also, the development of a sustainable bioeconomy may encompass the application of plant gene technology and we discuss whether or not this is reflected in current associated national strategies. In addition, country-specific information about the opinion of the public and other stakeholders on plant gene technology is presented, together with a country-wise political comparison and a discussion of the potential reciprocal influence between public opinion and the political process of policy development. The Scandinavian region is unique in several aspects, such as climate and certain agriculturally related regulations, and at the same time the region is vulnerable to changes in plant breeding investments due to the relatively small market sizes. It is therefore important to discuss the role and regulation of innovative solutions in Scandinavian plant research and breeding.

Transcriptional control of anthocyanin biosynthesis genes and transcription factors associated with flower coloration patterns in Gerbera hybrida

We analyzed the expression of anthocyanin biosynthesis genes and transcription factors (TFs) in the Gerbera hybrida cultivars 'Bintang' and 'Alliance' that exhibit different coloration patterns. Differential expression of biosynthesis genes and TFs was associated with variable anthocyanin content at different flower developmental stages (S1-S3) in both cultivars; higher anthocyanin content was correlated with higher levels of gene expression. Exposure to different temperatures (6 and 22 °C) also resulted in different anthocyanin content levels: the lower temperature (6 °C) enhanced anthocyanin content compared to the higher temperature (22 °C). However, the increased anthocyanin content of 'Bintang' compared to 'Alliance' was the result of higher levels of expression of all detected genes, regardless of flower stage and temperature conditions. Therefore, we conclude that transcriptional control of the detected genes is associated with the mechanisms of anthocyanin biosynthesis and coloration patterns in gerberas; however, further studies of the key genes are needed.

Genetically engineered orange petunias on the market

Unauthorized genetically engineered orange petunias were found on the market. Genetic engineering of petunia was shown to lead to novel flower color some 20 years ago. Here we show that petunia lines with orange flowers, generated for scientific purposes, apparently found their way to petunia breeding programmes, intentionally or unintentionally. Today they are widely available, but have not been registered for commerce.

Molecular and functional characterization of two isoforms of chalcone synthase and their expression analysis in relation to flavonoid constituents in Grewia asiatica L

Chalcone synthase constitutes a functionally diverse gene family producing wide range of flavonoids by catalyzing the initial step of the phenylpropanoid pathway. There is a pivotal role of flavonoids in pollen function as they are imperative for pollen maturation and pollen tube growth during sexual reproduction in flowering plants. Here we focused on medicinally important fruit-bearing shrub Grewia asiatica. It is a rich repository of flavonoids. The fruits are highly acclaimed for various putative health benefits. Despite its importance, full commercial exploitation is hampered due to two drawbacks which include short shelf life of its fruits and larger seed volume. To circumvent these constraints, seed abortion is one of the viable options. Molecular interventions tested in a number of economic crops have been to impair male reproductive function by disrupting the chalcone synthase (CHS) gene activity. Against this backdrop the aim of the present study included cloning and characterization of two full-length cDNA clones of GaCHS isoforms from the CHS multigene family. These included GaCHS1 (NCBI acc. KX129910) and GaCHS2 (NCBI acc. KX129911) with an ORF of 1176 and 1170 bp, respectively. GaCHSs were heterologously expressed and purified in E. coli to validate their functionality. Functionality of CHS isoforms was also characterized via enzyme kinetic studies using five different substrates. We observed differential substrate specificities in terms of their Km and Vmax values. Accumulation of flavonoid constituents naringenin and quercetin were also quantified and their relative concentrations corroborated well with the expression levels of GaCHSs. Further, our results demonstrate that GaCHS isoforms show differential expression patterns at different reproductive phenological stages. Transcript levels of GaCHS2 were more than its isoform GaCHS1 at the anthesis stage of flower development pointing towards its probable role in male reproductive maturity.

Functional characterization and expression of GASCL1 and GASCL2, two anther-specific chalcone synthase like enzymes from Gerbera hybrida

The chalcone synthase superfamily consists of type III polyketidesynthases (PKSs), enzymes responsible for producing plant secondary metabolites with various biological and pharmacological activities. Anther-specific chalcone synthase-like enzymes (ASCLs) represent an ancient group of type III PKSs involved in the biosynthesis of sporopollenin, the main component of the exine layer of moss spores and mature pollen grains of seed plants. In the latter, ASCL proteins are localized in the tapetal cells of the anther where they participate in sporopollenin biosynthesis and exine formation within the locule. It is thought that the enzymes responsible for sporopollenin biosynthesis are highly conserved, and thus far, each angiosperm species with a genome sequenced has possessed two ASCL genes, which in Arabidopsis thaliana are PKSA and PKSB. The Gerbera hybrida (gerbera) PKS protein family consists of three chalcone synthases (GCHS1, GCHS3 and GCHS4) and three 2-pyrone synthases (G2PS1, G2PS2 and G2PS3). In previous studies we have demonstrated the functions of chalcone synthases in flavonoid biosynthesis, and the involvement of 2-pyrone synthases in the biosynthesis of antimicrobial compounds found in gerbera. In this study we expanded the gerbera PKS-family by functionally characterizing two gerbera ASCL proteins. In vitro enzymatic studies using purified recombinant proteins showed that both GASCL1 and GASCL2 were able to use medium and long-chain acyl-CoA starters and perform two to three condensation reactions of malonyl-CoA to produce tri- and tetraketide 2-pyrones, usually referred to as alpha-pyrones in sporopollenin literature. Both GASCL1 and GASCL2 genes were expressed only in floral organs, with most expression observed in anthers. In the anthers, transcripts of both genes showed strict tapetum-specific localization.

Related allopolyploids display distinct floral pigment profiles and transgressive pigments

PREMISE OF THE STUDY

Both polyploidy and shifts in floral color have marked angiosperm evolution. Here, we investigate the biochemical basis of the novel and diverse floral phenotypes seen in allopolyploids in Nicotiana (Solanaceae) and examine the extent to which the merging of distinct genomes alters flavonoid pigment production.

METHODS

We analyzed flavonol and anthocyanin pigments from Nicotiana allopolyploids of different ages (N. tabacum, 0.2 million years old; several species from Nicotiana section Repandae, 4.5 million years old; and five lines of first-generation synthetic N. tabacum) as well as their diploid progenitors.

KEY RESULTS

Allopolyploid floral pigment profiles tend not to overlap with their progenitors or related allopolyploids, and allopolyploids produce transgressive pigments that are not present in either progenitor. Differences in floral color among N. tabacum accessions seems mainly to be due to variation in cyanidin concentration, but changes in flavonol concentrations among accessions are also present.

CONCLUSIONS

Competition for substrates within the flavonoid biosynthetic pathway to make either flavonols or anthocyanins may drive the differences seen among related allopolyploids. Some of the pigment differences observed in allopolyploids may be associated with making flowers more visible to nocturnal pollinators.

Dihydroflavonol 4-Reductase Genes from Freesia hybrida Play Important and Partially Overlapping Roles in the Biosynthesis of Flavonoids

Dihydroflavonol-4-reductase (DFR) is a key enzyme in the reduction of dihydroflavonols to leucoanthocyanidins in both anthocyanin biosynthesis and proanthocyanidin accumulation. In many plant species, it is encoded by a gene family, however, how the different copies evolve either to function in different tissues or at different times or to specialize in the use of different but related substrates needs to be further investigated, especially in monocot plants. In this study, a total of eight putative DFR-like genes were firstly cloned from Freesia hybrida. Phylogenetic analysis showed that they were classified into different branches, and FhDFR1, FhDFR2, and FhDFR3 were clustered into DFR subgroup, whereas others fell into the group with cinnamoyl-CoA reductase (CCR) proteins. Then, the functions of the three FhDFR genes were further characterized. Different spatio-temporal transcription patterns and levels were observed, indicating that the duplicated FhDFR genes might function divergently. After introducing them into Arabidopsis dfr (tt3-1) mutant plants, partial complementation of the loss of cyanidin derivative synthesis was observed, implying that FhDFRs could convert dihydroquercetin to leucocyanidin in planta. Biochemical assays also showed that FhDFR1, FhDFR2, and FhDFR3 could utilize dihydromyricetin to generate leucodelphinidin, while FhDFR2 could also catalyze the formation of leucocyanidin from dihydrocyanidin. On the contrary, neither transgenic nor biochemical analysis demonstrated that FhDFR proteins could reduce dihydrokaempferol to leucopelargonidin. These results were consistent with the freesia flower anthocyanin profiles, among which delphinidin derivatives were predominant, with minor quantities of cyanidin derivatives and undetectable pelargonidin derivatives. Thus, it can be deduced that substrate specificities of DFRs were the determinant for the categories of anthocyanins aglycons accumulated in F. hybrida. Furthermore, we also found that the divergence of the expression patterns for FhDFR genes might be controlled at transcriptional level, as the expression of FhDFR1/FhDFR2 and FhDFR3 was controlled by a potential MBW regulatory complex with different activation efficiencies. Therefore, it can be concluded that the DFR-like genes from F. hybrida have diverged during evolution to play partially overlapping roles in the flavonoid biosynthesis, and the results will contribute to the study of evolution of DFR gene families in angiosperms, especially for monocot plants.

In silico study for diversing the molecular pathway of pigment formation: an alternative to manual coloring in cotton fibers

Diversity of colors in flowers and fruits is largely due to anthocyanin pigments. The flavonoid/anthocyanin pathway has been most extensively studied. Dihydroflavonol 4-reductase (DFR) is a vital enzyme of the flavonoid pathway which displays major impact on the formation of anthocyanins, flavan 3-ols and flavonols. The substrate specificity of the DFR was found to play a crucial role in determination of type of anthocyanidins. Altering the flavonoid/anthocyanin pathway through genetic engineering to develop color of our own choice is an exciting subject of future research. In the present study, comparison among four DFR genes (Gossypium hirsutum, Iris × hollandica, Ang. DFRI and DFRII), sequence alignment for homology as well as protein modeling and docking is demonstrated. Estimation of catalytic sites, prediction of substrate preference and protein docking were the key features of this article. For specific substrate uptake, a proline rich region and positions 12 plus 26 along with other positions emphasizing the 26-amino acid residue region (132-157) was tested. Results showed that proline rich region position 12, 26, and 132-157 plays an important role in selective attachment of DFRs with respective substrates. Further, "Expasy ProtParam tool" results showed that Iris × hollandica DFR amino acids (Asn 9: Asp 23) are favorable for reducing DHQ and DHM thus accumulating delphinidin, while Gossypium hirsutum DFR has (Asn 13: Asp 21) hypothesized to consume DHK. Protein docking data showed that amino acid residues in above mentioned positions were just involved in attachment of DFR with substrate and had no role in specific substrate uptake. Advanced bioinformatics analysis has revealed that all above mentioned positions have role in substrate attachment. For substrate specificity, other residues region is involved. It will help in color manipulations in different plant species.

Anthocyanin biosynthesis in gerbera cultivar 'Estelle' and its acyanic sport 'Ivory'

Identification of distinct allelic versions for dihydroflavonol 4-reductase in gerbera cultivars reveals that gerbera DFR enzymes have strong substrate preference in vivo that is not reflected to the activity in vitro. Flavonoids in the model ornamental plant Gerbera hybrida consist of flavones, flavonols and anthocyanins. Anthocyanins accumulate in the adaxial epidermis of petals and give the different cultivars their characteristic red and violet colour. Both pelargonidin and cyanidin derivatives are found in gerbera, but none of the cultivars contain delphinidin. 'Ivory', a cultivar with white petals, is a sport of the pelargonidin-containing pink cultivar 'Estelle', i.e. it originates from an acyanic branch of 'Estelle'. In this work, four different alleles encoding dihydroflavonol 4-reductase (DFR) were identified in gerbera cultivars. We found that, in contrast to 'Estelle' with the functional allele GDFR1-2, 'Ivory' carries a mutation in this gene that results in an inactive enzyme. Interestingly, 'Ivory' also expresses a second, nonmutated allele (GDFR1-3) in petal epidermi, leading to extractable DFR activity but not to anthocyanin biosynthesis. The second allele encodes a protein identical in amino acid sequence to the DFR of the cyanidin-containing variety 'President'. Pelargonidin-containing cultivars do not react to the flavonoid 3'-hydroxylase inhibitor tetcyclacis, but cyanidin-containing cultivars lose their colour, instead of starting to synthesise pelargonidins, indicating the specificity of GDFR1-3 for the cyanidin pathway. This explains why petals of 'Ivory' are white, even when it has lost only one of the two enzymatically functional DFR forms, and shows that anthocyanin biosynthesis in gerbera is under more complex regulation than earlier thought.

Functional diversification of duplicated CYC2 clade genes in regulation of inflorescence development in Gerbera hybrida (Asteraceae)

The complex inflorescences (capitula) of Asteraceae consist of different types of flowers. In Gerbera hybrida (gerbera), the peripheral ray flowers are bilaterally symmetrical and lack functional stamens while the central disc flowers are more radially symmetrical and hermaphroditic. Proteins of the CYC2 subclade of the CYC/TB1-like TCP domain transcription factors have been recruited several times independently for parallel evolution of bilaterally symmetrical flowers in various angiosperm plant lineages, and have also been shown to regulate flower-type identity in Asteraceae. The CYC2 subclade genes in gerbera show largely overlapping gene expression patterns. At the level of single flowers, their expression domain in petals shows a spatial shift from the dorsal pattern known so far in species with bilaterally symmetrical flowers, suggesting that this change in expression may have evolved after the origin of Asteraceae. Functional analysis indicates that GhCYC2, GhCYC3 and GhCYC4 mediate positional information at the proximal-distal axis of the inflorescence, leading to differentiation of ray flowers, but that they also regulate ray flower petal growth by affecting cell proliferation until the final size and shape of the petals is reached. Moreover, our data show functional diversification for the GhCYC5 gene. Ectopic activation of GhCYC5 increases flower density in the inflorescence, suggesting that GhCYC5 may promote the flower initiation rate during expansion of the capitulum. Our data thus indicate that modification of the ancestral network of TCP factors has, through gene duplications, led to the establishment of new expression domains and to functional diversification.

Functional diversification of duplicated chalcone synthase genes in anthocyanin biosynthesis of Gerbera hybrida

• Chalcone synthase (CHS) is the key enzyme in the first committed step of the flavonoid biosynthetic pathway and catalyzes the stepwise condensation of 4-coumaroyl-CoA and malonyl-CoA to naringenin chalcone. In plants, CHS is often encoded by a small family of genes that are temporally and spatially regulated. Our earlier studies have shown that GCHS4 is highly activated by ectopic expression of an MYB-type regulator GMYB10 in gerbera (Gerbera hybrida). • The tissue- and development-specific expression patterns of three gerbera CHS genes were examined. Virus-induced gene silencing (VIGS) was used to knock down GCHS1 and GCHS4 separately in gerbera inflorescences. • Our data show that GCHS4 is the only CHS encoding gene that is expressed in the cyanidin-pigmented vegetative tissues of gerbera cv Terraregina. GCHS3 expression is pronounced in the pappus bristles of the flowers. Expression of both GCHS1 and GCHS4 is high in the epidermal cells of gerbera petals, but only GCHS1 is contributing to flavonoid biosynthesis. • Gerbera contains a family of three CHS encoding genes showing different spatial and temporal regulation. GCHS4 expression in gerbera petals is regulated post-transcriptionally, at the level of either translation elongation or protein stability.

Transcriptome analysis of Gerbera hybrida ray florets: putative genes associated with gibberellin metabolism and signal transduction

In this study, the transcriptome of the Gerbera hybrida ray floret was constructed using a high-throughput Illumina sequencing platform. All 47,104 UniGenes with an average length of 845 nt and an N50 equaling 1321 nt were generated from 72,688,546 total primary reads after filtering and assembly. A total of 36,693 transcripts were annotated by comparison with non-redundant National Center for Biotechnology Information (NCBI) protein (Nr), non-redundant NCBI nucleotide (Nt), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases after removing exogenous contaminated sequences. The majority of the genes that are associated with gibberellin metabolism and signal transduction were identified. The targets for signal transduction of other plant hormones were also enumerated. Our study provides a systematic overview of the hormone signal transduction genes that are involved in ray floral development in Asteraceae and should facilitate further understanding of the crucial roles of phytohormones in plant growth.

Flower colour and cytochromes P450

Cytochromes P450 play important roles in biosynthesis of flavonoids and their coloured class of compounds, anthocyanins, both of which are major floral pigments. The number of hydroxyl groups on the B-ring of anthocyanidins (the chromophores and precursors of anthocyanins) impact the anthocyanin colour, the more the bluer. The hydroxylation pattern is determined by two cytochromes P450, flavonoid 3'-hydroxylase (F3'H) and flavonoid 3',5'-hydroxylase (F3'5'H) and thus they play a crucial role in the determination of flower colour. F3'H and F3'5'H mostly belong to CYP75B and CYP75A, respectively, except for the F3'5'Hs in Compositae that were derived from gene duplication of CYP75B and neofunctionalization. Roses and carnations lack blue/violet flower colours owing to the deficiency of F3'5'H and therefore lack the B-ring-trihydroxylated anthocyanins based upon delphinidin. Successful redirection of the anthocyanin biosynthesis pathway to delphinidin was achieved by expressing F3'5'H coding regions resulting in carnations and roses with novel blue hues that have been commercialized. Suppression of F3'5'H and F3'H in delphinidin-producing plants reduced the number of hydroxyl groups on the anthocyanidin B-ring resulting in the production of monohydroxylated anthocyanins based on pelargonidin with a shift in flower colour to orange/red. Pelargonidin biosynthesis is enhanced by additional expression of a dihydroflavonol 4-reductase that can use the monohydroxylated dihydrokaempferol (the pelargonidin precursor). Flavone synthase II (FNSII)-catalysing flavone biosynthesis from flavanones is also a P450 (CYP93B) and contributes to flower colour, because flavones act as co-pigments to anthocyanins and can cause blueing and darkening of colour. However, transgenic plants expression of a FNSII gene yielded paler flowers owing to a reduction of anthocyanins because flavanones are precursors of anthocyanins and flavones.

Characterization of a heavy-ion induced white flower mutant of allotetraploid Nicotiana tabacum

KEY MESSAGE : We characterized a white flower mutant of allotetraploid N. tabacum as a DFR-deficient mutant; one copy of DFR has a cultivar-specific frameshift, while the other was deleted by heavy-ion irradiation. In most plants, white-flowered mutants have some kind of deficiency or defect in their anthocyanin biosynthetic pathway. Nicotiana tabacum normally has pink petals, in which cyanidin is the main colored anthocyanidin. When a relevant gene in the cyanidin biosynthetic pathway is mutated, the petals show a white color. Previously, we generated white-flowered mutants of N. tabacum by heavy-ion irradiation, which is accepted as an effective mutagen. In this study, we determined which gene was responsible for the white-flowered phenotype of one of these mutants, cv. Xanthi white flower 1 (xwf1). Southern blot analysis using a DNA fragment of the dihydroflavonol 4-reductase (DFR) gene as a probe showed that the xwf1 mutant lacked signals that were present in wild-type genomic DNAs. Sequence analysis demonstrated that one copy of the DFR gene (NtDFR2) was absent from the genome of the xwf1 mutant. The other copy of the DFR gene (NtDFR1) contained a single-base deletion resulting in a frameshift mutation, which is a spontaneous mutation in cv. Xanthi. Introduction of NtDFR2 cDNA into the petal limbs of xwf1 by particle bombardment resulted in production of the pink-colored cells, whereas introduction of NtDFR1 cDNA did not. These results indicate that xwf1 is a DFR-deficient mutant. One copy of NtDFR1 harbors a spontaneous frameshift mutation, while the other copy of NtDFR2 was deleted by heavy-ion beam irradiation.

Virus-induced gene silencing for Asteraceae--a reverse genetics approach for functional genomics in Gerbera hybrida

Virus-induced gene silencing (VIGS) is a natural defence mechanism in plants which leads to sequence-specific degradation of viral RNA. For identifying gene functions, Tobacco rattle virus (TRV)-based VIGS has been applied for silencing of endogenous genes in many plant species. Gerbera hybrida (Asteraceae) has emerged as a novel model for studies in flower development and secondary metabolism. For this highly heterozygous species, functional studies have been conducted through reverse genetic methods by producing stable transgenic lines, which, however, is labour-intensive and time-consuming. For the development of TRV-based VIGS system for gerbera, and for the first time for an Asteraceaeous species, we screened several gerbera cultivars and optimized the agroinfiltration methods for efficient silencing. Gene fragments for gerbera phytoene desaturase (GPDS) and Mg-chelatase subunits (GChl-H and GChl-I), expressed from a TRV vector, induced silencing phenotypes in leaves, scapes, and involucral bracts indicating their feasibility as markers for green tissues. In addition, robust silencing symptoms were achieved in gerbera floral tissues by silencing the anthocyanin pathway gene for chalcone synthase (GCHS1) and a gerbera B-type MADS-box gene globosa (GGLO1), confirming the phenotypes previously observed in stable transgenic lines. Unexpectedly, photobleaching induced by GPDS and GChl-H or GChl-I silencing, or by the herbicide norflurazon, resulted in silencing of the polyketide synthase gene G2PS1, which has no apparent connections to carotenoid or chlorophyll biosynthesis. We have shown feasibility of VIGS for functional studies in gerbera, but our results also show that selection of the marker gene for silencing must be critically evaluated.

Evolution and diversification of the CYC/TB1 gene family in Asteraceae--a comparative study in Gerbera (Mutisieae) and sunflower (Heliantheae)

Plant-specific TCP domain transcription factors have been shown to regulate morphological novelties during plant evolution, including the complex architecture of the Asteraceae inflorescence that involves different types of flowers. We conducted comparative analysis of the CYCLOIDEA/TEOSINTE BRANCHED1 (CYC/TB1) gene family in Gerbera hybrida (gerbera) and Helianthus annuus (sunflower), two species that represent distant tribes within Asteraceae. Our data confirm that the CYC/TB1 gene family has expanded in Asteraceae, a condition that appears to be connected with the increased developmental complexity and evolutionary success of this large plant family. Phylogenetic analysis of the CYC/TB1 gene family revealed both shared and lineage-specific duplications in gerbera and sunflower, corresponding to the three gene lineages previously identified as specific to core eudicots: CYC1, CYC2, and CYC3. Expression analyses of early stages of flower primordia development indicated that especially within the CYC2 clade, with the greatest number of secondary gene duplications, gene expression patterns are conserved between the species and associated with flower and inflorescence development. All sunflower and gerbera CYC2 clade genes showed differential expression between developing flower types, being upregulated in marginal ray (and trans) flowers. One gene in gerbera (GhCYC3) and two in sunflower (HaCYC2d and HaCYC2c) were indicated to be strong candidates as regulators of ray flower identity, a function that is specific for Asteraceae. Our data further showed that other CYC2 clade genes are likely to have more specialized functions at the level of single flowers, including the late functions in floral reproductive organs that may be more conserved across plant families. The expression patterns of CYC1 and CYC3 clade genes showed more differences between the two species but still pointed to possible conserved functions during vegetative plant development. Pairwise protein-protein interaction assays gave the first molecular evidence that CYC/TB1-like proteins function in complexes. Compared with sunflower, the gerbera proteins showed higher capacity for dimerization, between as well as within CYC clades. Our data from two distant species within the Asteraceae suggest that the expansion and the apparent conservation of especially the CYC2 clade CYC/TB1-like genes are associated with the evolution of the increased complexity of the Asteraceae inflorescence architecture.

Over-expression of the Gerbera hybrida At-SOC1-like1 gene Gh-SOC1 leads to floral organ identity deterioration

BACKGROUND AND AIMS

The family of MADS box genes is involved in a number of processes besides controlling floral development. In addition to supplying homeotic functions defined by the ABC model, they influence flowering time and transformation of vegetative meristem into inflorescence meristem, and have functions in roots and leaves. Three Gerbera hybrida At-SOC1-like genes (Gh-SOC1-Gh-SOC3) were identified among gerbera expressed sequence tags.

METHODS

Evolutionary relationships between SOC1-like genes from gerbera and other plants were studied by phylogenetic analysis. The function of the gerbera gene Gh-SOC1 in gerbera floral development was studied using expression analysis, protein-protein interaction assays and reverse genetics. Transgenic gerbera lines over-expressing or downregulated for Gh-SOC1 were obtained using Agrobacterium transformation and investigated for their floral phenotype.

KEY RESULTS

Phylogenetic analysis revealed that the closest paralogues of At-SOC1 are Gh-SOC2 and Gh-SOC3. Gh-SOC1 is a more distantly related paralogue, grouping together with a number of other At-SOC1 paralogues from arabidopsis and other plant species. Gh-SOC1 is inflorescence abundant and no expression was seen in vegetative parts of the plant. Ectopic expression of Gh-SOC1 did not promote flowering, but disturbed the development of floral organs. The epidermal cells of ray flower petals appeared shorter and their shape was altered. The colour of ray flower petals differed from that of the wild-type petals by being darker red on the adaxial side and greenish on the abaxial surface. Several protein-protein interactions with other gerbera MADS domain proteins were identified.

CONCLUSIONS

The At-SOC1 paralogue in gerbera shows a floral abundant expression pattern. A late petal expression might indicate a role in the final stages of flower development. Over-expression of Gh-SOC1 led to partial loss of floral identity, but did not affect flowering time. Lines where Gh-SOC1 was downregulated did not show a phenotype. Several gerbera MADS domain proteins interacted with Gh-SOC1.

A genomic approach to study anthocyanin synthesis and flower pigmentation in passionflowers

Most of the plant pigments ranging from red to purple colors belong to the anthocyanin group of flavonoids. The flowers of plants belonging to the genus Passiflora (passionflowers) show a wide range of floral adaptations to diverse pollinating agents, including variation in the pigmentation of floral parts ranging from white to red and purple colors. Exploring a database of expressed sequence tags obtained from flower buds of two divergent Passiflora species, we obtained assembled sequences potentially corresponding to 15 different genes of the anthocyanin biosynthesis pathway in these species. The obtained sequences code for putative enzymes are involved in the production of flavonoid precursors, as well as those involved in the formation of particular ("decorated") anthocyanin molecules. We also obtained sequences encoding regulatory factors that control the expression of structural genes and regulate the spatial and temporal accumulation of pigments. The identification of some of the putative Passiflora anthocyanin biosynthesis pathway genes provides novel resources for research on secondary metabolism in passionflowers, especially on the elucidation of the processes involved in floral pigmentation, which will allow future studies on the role of pigmentation in pollinator preferences in a molecular level.

Polyketide derivatives active against Botrytis cinerea in Gerbera hybrida

A previously isolated cDNA molecule from Gerbera hybrida (Asteraceae) codes for a new chalcone synthase-like polyketide synthase, 2-pyrone synthase (2PS). 2PS is able to synthesise 4-hydroxy-6-methyl-2-pyrone (triacetolactone), a putative precursor for gerberin and parasorboside, two abundant glucosides in gerbera. In this study, we show that gerbera plants transformed with the gene for 2PS in an antisense orientation and unable to synthesise gerberin and parasorboside are susceptible to Botrytis cinerea infection. In addition to the preformed glucosides, the transgenic plants also lack several compounds that are induced in control plants when infected with the mould. Some of these induced substances are effective in inhibiting fungal growth both in vitro and in vivo. Two of the phytoalexins were identified as the aglycones of gerberin and trans-parasorboside. The third phytoalexin is a rare coumarin, 4-hydroxy-5-methylcoumarin; however, it is typical of many plants of the sunflower family Asteraceae. The coumarin cannot be structurally derived from either gerberin or parasorboside, but may be derived from a related polyketide intermediate.

Transcriptional control of the dihydroflavonol 4-reductase multigene family in Lotus japonicus

In the genome of the model legume Lotus japonicus, dihydroflavonol 4-reductase (DFR), which is the first committed enzyme of the anthocyanin and proanthocyanidin (PA) pathways, is encoded as a tandemly arrayed five-gene family. Expression analysis revealed that both organ specificity and stress responsiveness differ among the DFRs. To elucidate the regulatory mechanisms underlying the expression of DFRs, we investigated the transcriptional control of each member of the DFR multigene family. Ectopic expression of a combination of the transcription factors MYB, bHLH, and WDR showed that only the DFR2 promoter was activated, indicating that each member of the DFR gene family is regulated independently.

Large scale interaction analysis predicts that the Gerbera hybrida floral E function is provided both by general and specialized proteins

BACKGROUND

The ornamental plant Gerbera hybrida bears complex inflorescences with morphologically distinct floral morphs that are specific to the sunflower family Asteraceae. We have previously characterized several MADS box genes that regulate floral development in Gerbera. To study further their behavior in higher order complex formation according to the quartet model, we performed yeast two- and three-hybrid analysis with fourteen Gerbera MADS domain proteins to analyze their protein-protein interaction potential.

RESULTS

The exhaustive pairwise interaction analysis showed significant differences in the interaction capacity of different Gerbera MADS domain proteins compared to other model plants. Of particular interest in these assays was the behavior of SEP-like proteins, known as GRCDs in Gerbera. The previously described GRCD1 and GRCD2 proteins, which are specific regulators involved in stamen and carpel development, respectively, showed very limited pairwise interactions, whereas the related GRCD4 and GRCD5 factors displayed hub-like positions in the interaction map. We propose GRCD4 and GRCD5 to provide a redundant and general E function in Gerbera, comparable to the SEP proteins in Arabidopsis. Based on the pairwise interaction data, combinations of MADS domain proteins were further subjected to yeast three-hybrid assays. Gerbera B function proteins showed active behavior in ternary complexes. All Gerbera SEP-like proteins with the exception of GRCD1 were excellent partners for B function proteins, further implicating the unique role of GRCD1 as a whorl- and flower-type specific C function partner.

CONCLUSIONS

Gerbera MADS domain proteins exhibit both conserved and derived behavior in higher order protein complex formation. This protein-protein interaction data can be used to classify and compare Gerbera MADS domain proteins to those of Arabidopsis and Petunia. Combined with our reverse genetic studies of Gerbera, these results reinforce the roles of different genes in the floral development of Gerbera. Building up the elaborate capitulum of Gerbera calls for modifications and added complexity in MADS domain protein behavior compared to the more simple flowers of, e.g., Arabidopsis.

Characterization of SQUAMOSA-like genes in Gerbera hybrida, including one involved in reproductive transition

BACKGROUND

The flowering process in plants proceeds through the induction of an inflorescence meristem triggered by several pathways. Many of the genes associated with both the flowering process and floral architecture encode transcription factors of the MADS domain family. Gerbera, a member of the sunflower family, Asteraceae, bears compressed inflorescence heads (capitula) with three different flower types characterized by differences in both sexuality and floral symmetry. To understand how such a complex inflorescence structure is achieved at the molecular level, we have characterized the array of Gerbera MADS box genes. The high number of SQUAMOSA-like genes in Gerbera compared to other model species raised the question as to whether they may relate to Gerbera's complex inflorescence structure and whether or not a homeotic A function is present.

RESULTS

In this paper we describe six Gerbera genes related to the SQUAMOSA/APETALA1/FRUITFULL genes of snapdragon and Arabidopsis. Based on phylogenetic analysis of the entire gene lineage, our data indicates that GSQUA1 and GSQUA3 are members of the SQUA/AP1 clade, while GSQUA2, GSQUA4, GSQUA5 and GSQUA6 are co-orthologs of the Arabidopsis FUL gene. GSQUA1/GSQUA3 and GSQUA4/GSQUA5/GSQUA6, respectively, represent several gene duplication events unknown in the model systems that may be specific to either Gerbera or Asteraceae. GSQUA genes showed specific expression profiles. GSQUA1, GSQUA2, and GSQUA5 were inflorescence abundant, while GSQUA3, GSQUA4, and GSQUA6 expression was also detected in vegetative organs. Overexpression of GSQUA2 in Gerbera led to accelerated flowering, dwarfism and vegetative abnormalities, all new and specific phenomena observed in transgenic Gerbera plants with modified MADS box gene expression.

CONCLUSIONS

Based on expression patterns, none of the Gerbera SQUA-like genes are likely to control flower organ identity in the sense of the floral A function. However, our data shows that the FUL-like gene GSQUA2 plays a vital role in meristem transition. The roles of other GSQUA-genes in Gerbera floral development are intriguing, but require still further study.

Functional characterization of B class MADS-box transcription factors in Gerbera hybrida

According to the classical ABC model, B-function genes are involved in determining petal and stamen development. Most core eudicot species have B class genes belonging to three different lineages: the PI, euAP3, and TM6 lineages, although both Arabidopsis and Antirrhinum appear to have lost their TM6-like gene. Functional studies were performed for three gerbera (Gerbera hybrida) B class MADS-box genes--PI/GLO-like GGLO1, euAP3 class GDEF2, and TM6-like GDEF1--and data are shown for a second euAP3-like gene, GDEF3. In phylogenetic analysis, GDEF3 is a closely related paralogue of GDEF2, and apparently stems from a duplication common to all Asteraceae. Expression analysis and transgenic phenotypes confirm that GGLO1 and GDEF2 mediate the classical B-function since they determine petal and stamen identities. However, based on assays in yeast, three B class heterodimer combinations are possible in gerbera. In addition to the interaction of GGLO1 and GDEF2 proteins, GGLO1 also pairs with GDEF1 and GDEF3. This analysis of GDEF1 represents the first functional characterization of a TM6-like gene in a core eudicot species outside Solanaceae. Similarly to its relatives in petunia and tomato, the expression pattern and transgenic phenotypes indicate that GDEF1 is not involved in determination of petal identity, but has a redundant role in regulating stamen development.

Genetic engineering of novel flower colors in floricultural plants: recent advances via transgenic approaches

Since the first successful genetic engineering of flower color in petunia, several new techniques have been developed and applied to modify flower color not only in model plants but also in floricultural plants. A typical example is the commercial violet-flowered carnation "Moondust series" developed by Suntry Ltd. and Florigene Ltd. More recently, blue-flowered roses have been successfully produced and are expected to be commercially available in the near future. In recent years, successful modification of flower color by sophisticated regulation of flower-pigment metabolic pathways has become possible. In this chapter, we review recent advances in flower color modification by genetic engineering, especially focusing on the methodology. We have included our own recent results on successful production of flower-color-modified transgenic plants in a model plant, tobacco and an ornamental plant, gentian. Based on these results, genetic engineering of flower color for improvement of floricultural plants is discussed.

A TCP domain transcription factor controls flower type specification along the radial axis of the Gerbera (Asteraceae) inflorescence

Several key processes in plant development are regulated by TCP transcription factors. CYCLOIDEA-like (CYC-like) TCP domain proteins have been shown to control flower symmetry in distantly related plant lineages. Gerbera hybrida, a member of one of the largest clades of angiosperms, the sunflower family (Asteraceae), is an interesting model for developmental studies because its elaborate inflorescence comprises different types of flowers that have specialized structures and functions. The morphological differentiation of flower types involves gradual changes in flower size and symmetry that follow the radial organization of the densely packed inflorescence. Differences in the degree of petal fusion further define the distinct shapes of the Gerbera flower types. To study the role of TCP transcription factors during specification of this complex inflorescence organization, we characterized the CYC-like homolog GhCYC2 from Gerbera. The expression of GhCYC2 follows a gradient along the radial axis of the inflorescence. GhCYC2 is expressed in the marginal, bilaterally symmetrical ray flowers but not in the centermost disk flowers, which are nearly radially symmetrical and have significantly less fused petals. Overexpression of GhCYC2 causes disk flowers to obtain morphologies similar to ray flowers. Both expression patterns and transgenic phenotypes suggest that GhCYC2 is involved in differentiation among Gerbera flower types, providing the first molecular evidence that CYC-like TCP factors take part in defining the complex inflorescence structure of the Asteraceae, a major determinant of the family's evolutionary success.

Identification of target genes for a MYB-type anthocyanin regulator in Gerbera hybrida

Genetic modification of the flavonoid pathway has been used to produce novel colours and colour patterns in ornamental plants as well as to modify the nutritional and pharmaceutical properties of food crops. It has been suggested that co-ordinate control of multiple steps of the pathway with the help of regulatory genes would lead to a more predictable control of metabolic flux. Regulation of anthocyanin biosynthesis has been studied in a common ornamental plant, Gerbera hybrida (Asteraceae). An R2R3-type MYB factor, GMYB10, shares high sequence similarity and is phylogenetically grouped together with previously characterized regulators of anthocyanin pigmentation. Ectopic expression of GMYB10 leads to strongly enhanced accumulation of anthocyanin pigments as well as to an altered pigmentation pattern in transgenic gerbera plants. Anthocyanin analysis indicates that GMYB10 specifically induces cyanidin biosynthesis in undifferentiated callus and in vegetative tissues. Furthermore, in floral tissues enhanced pelargonidin production is detected. Microarray analysis using the gerbera 9K cDNA array revealed a highly predicted set of putative target genes for GMYB10 including new gene family members of both early and late biosynthetic genes of the flavonoid pathway. However, completely new candidate targets, such as a serine carboxypeptidase-like gene as well, as two new MYB domain factors, GMYB11 and GMYB12, whose exact function in phenylpropanoid biosynthesis is not clear yet, were also identified.

Production of red-flowered plants by genetic engineering of multiple flavonoid biosynthetic genes

Orange- to red-colored flowers are difficult to produce by conventional breeding techniques in some floricultural plants. This is due to the deficiency in the formation of pelargonidin, which confers orange to red colors, in their flowers. Previous researchers have reported that brick-red colored flowers can be produced by introducing a foreign dihydroflavonol 4-reductase (DFR) with different substrate specificity in Petunia hybrida, which does not accumulate pelargonidin pigments naturally. However, because these experiments used dihydrokaempferol (DHK)-accumulated mutants as transformation hosts, this strategy cannot be applied directly to other floricultural plants. Thus in this study, we attempted to produce red-flowered plants by suppressing two endogenous genes and expressing one foreign gene using tobacco as a model plant. We used a chimeric RNAi construct for suppression of two genes (flavonol synthase [FLS] and flavonoid 3'-hydroxylase [F3'H]) and expression of the gerbera DFR gene in order to accumulate pelargonidin pigments in tobacco flowers. We successfully produced red-flowered tobacco plants containing high amounts of additional pelargonidin as confirmed by HPLC analysis. The flavonol content was reduced in the transgenic plants as expected, although complete inhibition was not achieved. Expression analysis also showed that reduction of the two-targeted genes and expression of the foreign gene occurred simultaneously. These results demonstrate that flower color modification can be achieved by multiple gene regulation without use of mutants if the vector constructs are designed resourcefully.