A basic helix-loop-helix transcription factor DvIVS determines flower color intensity in cyanic dahlia cultivars

The transcription factor MfbHLH104 from Myrothamnus flabellifolia promotes drought tolerance of Arabidopsis thaliana by enhancing stability of the photosynthesis system

The resurrection plant Myrothamnus flabellifolia can survive extreme drought and desiccation conditions, and quickly recover after rewatering. However, little is known about the mechanism underlying the drought tolerance of M. flabellifolia. In this study, MfbHLH104 was cloned and introduced into Arabidopsis thaliana due to the lack of a transgenic system for M. flabellifolia. MfbHLH104 is localized in the nucleus. Its N-terminal region has transactivation ability in yeast, and the C-terminal region may inhibit the transactivation ability. Overexpressing MfbHLH104 significantly increased drought and salt tolerance of A. thaliana at both seedling and adult stages. It enhanced leaf water retention capacity by decreasing water loss rate and increasing drought- and abscisic acid (ABA) -induced stomatal closure. Additionally, it boosted osmolyte accumulation and ROS scavenging ability by up-regulating genes associated with osmolyte biosynthesis and antioxidant enzymes, and enhancing antioxidant enzyme activities. The expression of ABA-responsive genes were also promoted by MfbHLH104. Remarkably, RNA-seq analysis indicated that MfbHLH104 significantly up-regulated 32 genes (FDR < 0.05 and fold change ≥1.5) involved in photosynthesis related pathways (KEGG pathway No: ko00195, ko00196) under drought, which account for 18.7 % of the total up-regulated genes and the most enriched KEGG pathways. This result suggested that it may help to maintain the stability of the photosynthesis system under drought conditions.

The Influence of Technological Factors on the Structure and Chemical Composition of Tuberous Dahlia Roots Determined Using Vibrational Spectroscopy

This research investigated the structural and chemical modifications of Dahlia 'Kennemerland' across different technological conditions and throughout the vegetation period. Using FT-IR imaging, this study focused on the changes in the inulin, lignin, and suberin contents of tuberous roots. FT-IR maps were generated to visualize the distribution of these compounds across scanned areas, highlighting variations across cultivation methods and seasonal stages. The key compounds analyzed included inulin, lignin, and suberin, which were identified in different root zones. The results showed that inulin was distributed in all analyzed areas, predominantly in zone 1 (periderm), with a distribution that increased with forced cultivation, while lignin and suberin distributions varied with zone and season. Forced tuberous root lignin was detected in all four areas analyzed, in the fall accumulating mainly in area 4 and in suberin starting from summer until autumn. Based on the evaluation of the maps obtained by representing the area ratios of specific bands (inulin/lignin and inulin/suberin), we established where the inulin was present in the highest quantity and concluded that suberin was the constituent with the lowest concentration in tuberous Dahlia roots. These findings emphasize the influence of technological factors and seasonal changes on the biochemical makeup of tuberous Dahlia roots. This detailed biochemical mapping provides insights for optimizing Dahlia cultivation and storage for various industrial applications. This study concludes that FT-IR spectroscopy is an effective tool for monitoring and understanding the biochemical dynamics of Dahlia roots, aiding their agricultural and industrial utilization.

Identification of two 6'-deoxychalcone 4'-glucosyltransferase genes in dahlia (Dahlia variabilis)

MAIN CONCLUSION

Two glycosyltransferase genes belonging to UGT88 family were identified to have 6'-deoxychalcone 4'-glucosyltransferase activity in dahlia. 6'-Deoxychalcones (isoliquiritigenin and butein) are important pigments for yellow and orange to red flower color. 6'-Deoxychalcones are glucosylated at the 4'-position in vivo, but the genes encoding 6'-deoxychalcone 4'-glucosyltransferase have not yet been identified. In our previous study, it was indicated that snapdragon (Antirrhinum majus) chalcone 4'-O-glucosyltransferase (Am4'CGT) has isoliquiritigenin 4'-glucosylation activity. Therefore, to identify genes encoding 6'-deoxychalcone 4'-glucosyltransferase in dahlia (Dahlia variabilis), genes expressed in ray florets that shared high homology with Am4'CGT were explored. As a result, c34671_g1_i1 and c35662_g1_i1 were selected as candidate genes for 6'-deoxychalcone 4'-glucosyltransferases in dahlia. We conducted transient co-overexpression of three genes (c34671_g1_i1 or c35662_g1_i1, dahlia aldo-keto reductase1 (DvAKR1) or soybean (Glycine max) chalcone reductase5 (GmCHR5), and chili pepper (Capsicum annuum) MYB transcription factor (CaMYBA)) in Nicotiana benthamiana by agroinfiltration. Transient overexpression of c34671_g1_i1, DvAKR1, and CaMYBA resulted in increase in the accumulation of isoliquiritigenin 4'-glucosides, isoliquiritigenin 4'-O-glucoside, and isoliquiritigenin 4'-O-[6-O-(malonyl)-glucoside]. However, transient overexpression of c35662_g1_i1, DvAKR1, and CaMYBA did not increase accumulation of isoliquiritigenin 4'-glucosides. Using GmCHR5 instead of DvAKR1 showed similar results suggesting that c34671_g1_i1 has isoliquiritigenin 4'-glucosyltransferase activity. In addition, we conducted co-overexpression of four genes (c34671_g1_i1, c35662_g1_i1 or Am4'CGT, DvAKR1 or GmCHR5, CaMYBA, and chalcone 3-hydroxylase from dahlia). Accumulation of butein 4'-O-glucoside and butein 4'-O-[6-O-(malonyl)-glucoside] was detected for c35662_g1_i1, suggesting that c35662_g1_i1 has butein 4'-glucosyltransferase activity. Recombinant enzyme analysis also supported butein 4'-glucosyltransferases activity of c35662_g1_i1. Therefore, our results suggested that both c34671_g1_i1 and c35662_g1_i1 are 6'-deoxychalcone 4'-glucosyltransferases but with different substrate preference.

A novel aldo-keto reductase gene is involved in 6'-deoxychalcone biosynthesis in dahlia (Dahlia variabilis)

A novel gene belonging to the aldo-keto reductase 13 family is involved in isoliquiritigenin biosynthesis in dahlia. The yellow pigments of dahlia flowers are derived from 6'-deoxychalcones, which are synthesized via a two-step process, involving the conversion of 3-malonyl-CoA and 4-coumaloyl-CoA into isoliquiritigenin in the first step, and the subsequent generation of butein from isoliquiritigenin. The first step reaction is catalyzed by chalcone synthase (CHS) and aldo-keto reductase (AKR). AKR has been implicated in the isoflavone biosynthesis in legumes, however, isolation of butein biosynthesis related AKR members are yet to be reported. A comparative RNA-seq analysis between two dahlia cultivars, 'Shukuhai' and its butein-deficient lateral mutant 'Rinka', was used in this study to identify a novel AKR gene involved in 6'-deoxychalcone biosynthesis. DvAKR1 encoded a AKR 13 sub-family protein with significant differential expression levels, and was phylogenetically distinct from the chalcone reductases, which belongs to the AKR 4A sub-family in legumes. DNA sequence variation and expression profiles of DvAKR1 gene were correlated with 6'-deoxychalcone accumulation in the tested dahlia cultivars. A single over-expression analysis of DvAKR1 was not sufficient to initiate the accumulation of isoliquiritigenin in tobacco, in contrast, its co-overexpression with a chalcone 4'-O-glucosyltransferase (Am4'CGT) from Antirrhinum majus and a MYB transcription factor, CaMYBA from Capsicum annuum successfully induced isoliquiritigenin accumulation. In addition, DvAKR1 homologous gene expression was detected in Coreopsideae species accumulating 6'-deoxychalcone, but not in Asteraceae species lacking 6'-deoxychalcone production. These results not only demonstrate the involvement of DvAKR1 in the biosynthesis of 6'-deoxychalcone in dahlia, but also show that 6'-deoxychalcone occurrence in Coreopsideae species developed evolutionarily independent from legume species.

Identification of Candidate Genes Responsible for Flower Colour Intensity in Gentiana triflora

Gentians cultivated in Japan (Gentiana triflora and Gentiana scabra and hybrids) have blue flowers, but flower colour intensity differs among cultivars. The molecular mechanism underlying the variation in flower colour intensity is unclear. Here, we produced F₂ progeny derived from an F₁ cross of intense- and faint-blue lines and attempted to identify the genes responsible for flower colour intensity using RNA-sequencing analyses. Comparative analysis of flower colour intensity and transcriptome data revealed differentially expressed genes (DEGs), although known flavonoid biosynthesis-related genes showed similar expression patterns. From quantitative RT-PCR (qRT-PCR) analysis, we identified two and four genes with significantly different expression levels in the intense- and faint-blue flower lines, respectively. We conducted further analyses on one of the DEGs, termed GtMIF1, which encodes a putative mini zinc-finger protein homolog, which was most differently expressed in faint-blue individuals. Functional analysis of GtMIF1 was performed by producing stable tobacco transformants. GtMIF1-overexpressing tobacco plants showed reduced flower colour intensity compared with untransformed control plants. DNA-marker analysis also confirmed that the GtMIF1 allele of the faint-blue flower line correlated well with faint flower colour in F₂ progeny. These results suggest that GtMIF1 is one of the key genes involved in determining the flower colour intensity of gentian.

Nutritional and functional compounds in dahlia flowers and roots

Abstract The use of unconventional edible plants in human food has grown more widespread in recent years, driven mainly by gourmet dishes. Evidence of the food properties of these species is still scarce. Aiming to obtain more in-depth knowledge of dahlia plants, this study aimed to evaluate the nutritional, bioactive, and antinutritional properties of the edible parts of purple dahlia (tuberous root and flower) to elucidate their value and safety as foods. The percent composition, caloric value, pH, Total Soluble Solids (TSS), Total Titratable Acidity (TTA), ratio of TSS to TTA, anthocyanins, carotenoids, vitamin C, total phenolics, tannins, nitrates, and minerals of the roots and flowers were analyzed. The inulin content in the root and the color of the flower were also evaluated. The results were reported as mean and standard deviation, and exploratory factor analysis was performed. Both parts of the dahlia had constituents that contribute to a good diet at concentrations like those in conventional vegetables, whereas the antinutritional components were also compatible with those of commonly consumed foods, with acceptable dietary values. Thus, it is evident that purple dahlia flowers and roots have potential for use in human food and can be considered good options to improve and diversify a healthy diet.

Anthocyanins in Floral Colors: Biosynthesis and Regulation in Chrysanthemum Flowers

Chrysanthemum (Chrysanthemum morifolium) is an economically important ornamental crop across the globe. As floral color is the major factor determining customer selection, manipulation of floral color has been a major objective for breeders. Anthocyanins are one of the main pigments contributing to a broad variety of colors in the ray florets of chrysanthemum. Manipulating petal pigments has resulted in the development of a vast range of floral colors. Although the candidate genes involved in anthocyanin biosynthesis have been well studied, the genetic and transcriptional control of floral color remains unclear. Despite advances in multi-omics technology, these methods remain in their infancy in chrysanthemum, owing to its large complex genome and hexaploidy. Hence, there is a need to further elucidate and better understand the genetic and molecular regulatory mechanisms in chrysanthemum, which can provide a basis for future advances in breeding for novel and diverse floral colors in this commercially beneficial crop. Therefore, this review describes the significance of anthocyanins in chrysanthemum flowers, and the mechanism of anthocyanin biosynthesis under genetic and environmental factors, providing insight into the development of novel colored ray florets. Genetic and molecular regulatory mechanisms that control anthocyanin biosynthesis and the various breeding efforts to modify floral color in chrysanthemum are detailed.

Post-transcriptional silencing of chalcone synthase is involved in phenotypic lability in petals and leaves of bicolor dahlia (Dahlia variabilis) 'Yuino'

Post-transcriptional gene silencing (PTGS) of a chalcone synthase ( DvCHS2 ) occurred in the white part of bicolor petals and flavonoid-poor leaves; however, it did not in red petals and flavonoid-rich leaves. Petal color lability is a prominent feature of bicolor dahlia cultivars, and causes plants to produce not only original bicolor petals with colored bases and pure white tips, but also frequently single-colored petals without white tips. In this study, we analysed the molecular mechanisms that are associated with petal color lability using the red-white bicolor cultivar 'Yuino'. Red single-colored petals lose their white tips as a result of recover of flavonoid biosynthesis. Among flavonoid biosynthetic genes including four chalcone synthase (CHS)-like genes (DvCHS1, DvCHS2, DvCHS3, and DvCHS4), DvCHS1 and DvCHS2 had significantly lower expression levels in the white part of bicolor petals than in red petals, while DvCHS3, DvCHS4, and other flavonoid biosynthetic genes had almost the same expression levels. Small RNAs from the white part of a bicolor petal were mapped onto DvCHS1 and DvCHS2, while small RNAs from a red single-colored petal were not mapped onto any of the four CHS genes. A relationship between petal color and leaf flavonoid accumulation has previously been demonstrated, whereby red petal-producing plants accumulate flavonoids in their leaves, while bicolor petal-producing plants tend not to. The expression level of DvCHS2 was down-regulated in flavonoid-poor leaves and small RNAs from flavonoid-poor leaves were mapped onto DvCHS2, suggesting that the down-regulation of DvCHS2 in flavonoid-poor leaves occurs post-transcriptionally. Genomic analysis also suggested that DvCHS2 is the key gene involved in bicolor formation. Together, these results suggest that post-transcriptional gene silencing of DvCHS2 plays a key role in phenotypic lability in this bicolor dahlia.

Extensive Transcriptome Changes Underlying the Flower Color Intensity Variation in Paeonia ostii

Tree peonies are a group of traditional ornamental plants, especially in East Asia, with Paeonia ostii as one of the most important ancestral species. P. ostii has flowers with varying colors, ranging from nearly white, light pink to deep pink. However, few studies have been done to unravel the molecular mechanisms underlying the flower color intensity variation in plants. Based on comparative analyses of the pigment composition and transcriptomes of P. ostii with different flower color intensities, we found that the anthocyanin concentration was significantly correlated with the flower color intensity in P. ostii. Transcriptome analysis by RNA-Sequencing revealed 7187 genes that were differentially expressed between flowers with different color intensities. Functional enrichment analysis of differentially expressed genes revealed multiple pathways possibly responsible for color intensity variation in P. ostii, including flavonoid biosynthesis, fatty acid oxidation, carbohydrate metabolism, and hormone-mediated signaling. Particularly, while anthocyanin biosynthesis genes showing positive correlations between their expression and anthocyanin concentration in flowers, two transcription factors, PoMYB2 and PoSPL1, seem to negatively regulate anthocyanin accumulation by affecting the activation capacity of the MYB-bHLH-WDR complex, exhibiting an inverse relationship between their expression and anthocyanin accumulation. Our results showed that, although anthocyanin biosynthesis had a direct effect on the pigmentation of the P. ostii flower, other metabolic and hormone-mediated signaling pathways were also contributed to the flower color intensity variation in P. ostii, suggesting complex coordinated changes in the transcriptional network. Differential expression of genes encoding anthocyanin repressors seems to be the major factor responsible for the intensity variation in anthocyanin pigmentation in P. ostii.

A Novel bHLH Transcription Factor Involved in Regulating Anthocyanin Biosynthesis in Chrysanthemums (Chrysanthemum morifolium Ramat.)

Chrysanthemums (Chrysanthemum morifolium Ramat.) exhibit a variety of flower colors due to their differing abilities to accumulate anthocyanins. One MYB member, CmMYB6, has been verified as a transcription regulator of chrysanthemum genes involved in anthocyanin biosynthesis; however, the co-regulators for CmMYB6 remain unclear in chrysanthemum. Here, the expression pattern of CmbHLH2, which is clustered in the IIIf bHLH subgroup, was shown to be positively correlated with the anthocyanin content of cultivars with red, pink and yellow flower colors, respectively. CmbHLH2 significantly upregulated the CmDFR promoter and triggered anthocyanin accumulation when co-expressed with CmMYB6. Yeast one-hybrid analyses indicated that CmbHLH2 was able to bind directly to the CmDFR promoter. Moreover, yeast two-hybrid assays indicated protein-protein interaction between CmbHLH2 and CmMYB6. These results suggest that CmbHLH2 is the essential partner for CmMYB6 in regulating anthocyanin biosynthesis in chrysanthemum.

A "White" Anthocyanin-less Pomegranate (Punica granatum L.) Caused by an Insertion in the Coding Region of the Leucoanthocyanidin Dioxygenase (LDOX; ANS) Gene

Color is an important determinant of pomegranate fruit quality and commercial value. To understand the genetic factors controlling color in pomegranate, chemical, molecular and genetic characterization of a "white" pomegranate was performed. This unique accession is lacking the typical pomegranate color rendered by anthocyanins in all tissues of the plant, including flowers, fruit (skin and arils) and leaves. Steady-state gene-expression analysis indicated that none of the analyzed "white" pomegranate tissues are able to synthesize mRNA corresponding to the PgLDOX gene (leucoanthocyanidin dioxygenase, also called ANS, anthocyanidin synthase), which is one of the central structural genes in the anthocyanin-biosynthesis pathway. HPLC analysis revealed that none of the "white" pomegranate tissues accumulate anthocyanins, whereas other flavonoids, corresponding to biochemical reactions upstream of LDOX, were present. Molecular analysis of the "white" pomegranate revealed the presence of an insertion and an SNP within the coding region of PgLDOX. It was found that the SNP does not change amino acid sequence and is not fully linked with the "white" phenotype in all pomegranate accessions from the collection. On the other hand, genotyping of pomegranate accessions from the collection and segregating populations for the "white" phenotype demonstrated its complete linkage with the insertion, inherited as a recessive single-gene trait. Taken together, the results indicate that the insertion in PgLDOX is responsible for the "white" anthocyanin-less phenotype. These data provide the first direct molecular, genetic and chemical evidence for the effect of a natural modification in the LDOX gene on color accumulation in a fruit-bearing woody perennial deciduous tree. This modification can be further utilized to elucidate the physiological role of anthocyanins in protecting the tree organs from harmful environmental conditions, such as temperature and UV radiation.

Tobacco streak virus (strain dahlia) suppresses post-transcriptional gene silencing of flavone synthase II in black dahlia cultivars and causes a drastic flower color change

Tobacco streak virus suppressed post-transcriptional gene silencing and caused a flower color change in black dahlias, which supported the role of cyanidin-based anthocyanins for black flower appearance. Black flower color of dahlia (Dahlia variabilis) has been attributed, in part, to the high accumulation of cyanidin-based anthocyanins that occurs when flavone synthesis is reduced because of post-transcriptional gene silencing (PTGS) of flavone synthase II (DvFNS). There are also purple-flowering plants that have emerged from a black cultivar 'Kokucho'. We report that the purple color is not caused by a mutation, as previously thought, but by infection with tobacco streak virus (TSVdahlia), which suppresses the PTGS of DvFNS. When TSVdahlia was eliminated from the purple-flowering 'Kokucho' by leaf primordia-free shoot apical meristem culture, the resulting flowers were black. TSVdahlia-infected purple flowers had lower numbers of siRNAs to DvFNS than black flowers, suggesting that TSVdahlia has a silencing suppressor. The graft inoculation of other black cultivars with TSVdahlia altered their flower color drastically except for 'Fidalgo Blacky', a very deep black cultivar with the highest amount of cyanidin-based anthocyanins. The flowers of all six TSVdahlia-infected cultivars accumulated increased amounts of flavones and reduced amounts of cyanidin-based anthocyanins. 'Fidalgo Blacky' remained black despite the change in pigment accumulation, and the amounts of cyanidin-based anthocyanins in its TSVdahlia-infected plants were still higher than those of other cultivars. We propose that black flower color in dahlia is controlled by two different mechanisms that increase the amount of cyanidin-based anthocyanins: DvFNS PTGS-dependent and -independent mechanisms. If both mechanisms occur simultaneously, the flower color will be blacker than if only a single mechanism is active.

Sequencing and de novo assembly of a Dahlia hybrid cultivar transcriptome

Dahlia variabilis, with an exceptionally high diversity of floral forms and colors, is a popular flower amongst both commercial growers and hobbyists. Recently, some genetic controls of pigment patterns have been elucidated. These studies have been limited, however, by the lack of comprehensive transcriptomic resources for this species. Here we report the sequencing, assembly, and annotation of the transcriptome of the developing leaves, stems, and floral buds of D. variabilis. This resulted in 35,638 contigs, most of which seem to contain the complete coding sequence, and of which 20,881 could be successfully annotated by similarity to UniProt. Furthermore, we conducted a preliminary investigation to identify contigs with expression patterns consistent with tissue-specificity. These results will accelerate research into the genetic controls of pigmentation and floral form of D. variabilis.