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Cut dahlia (Dahlia Cav.) flowers have recently become popular, but their marketability has been limited due to their poor vase life. The purposes of this study were to clarify the roles of leaves and inflorescences in the senescence of cut dahlias and to discuss the sink-source relationship between vegetative organs and inflorescences. The leaf life was maintained much longer (16.7 days) than the inflorescence life (7.4 days). The inflorescence life was not affected by removal of leaves, while leaf life was prolonged (19.6 days) by removal of inflorescences. Sucrose, glucose, fructose and small quantities of myo-inositol were detected in florets, and in addition to these sugars, nystose and 1-kestose were detected in stems and leaves. Total sugar levels of the middle florets (14.5 mg·g⁻¹ FW on day 0) declined rapidly before their senescence. Total sugar levels of leaves (20.5 mg·g⁻¹ FW on day 0) and stems (19.0–22.5 mg·g⁻¹ FW on day 0) also decreased gradually during the postharvest period, but the levels decreased more slowly in deflowered cut stems. Sugar leakage from stem bases into vase water occurred during the initial few days. Removal of inflorescences increased sugar leakage significantly and promoted callus formation on the stem base. From these results, the inflorescence is considered to be a strong sink for carbohydrates, and stems and leaves serve as source organs. Heat girdling applied to the flower necks and petioles, also increased sugar concentrations of stem bases, thus resulting in higher sugar leakage and callus formation, although both heat girdling treatments shortened the leaf life. The sharp decrease in sugar levels of florets and an insufficient sugar supply are considered to be responsible for the short vase life of cut dahlias. It is suggested that these effects might be partly due to the blockage of sugar flows into petals through abscission layer development in the petal-ovary boundaries. Based on these results, we illustrate the senescin

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.

Betalain is one of four major plant pigments and shares some features with anthocyanin; however, no plant has been found to biosynthesize both pigments. Previous studies have reported that anthocyanin biosynthesis in some plants is regulated by post-transcriptional gene-silencing (PTGS), but the importance of PTGS in betalain biosynthesis remains unclear. In this study, we report the occurrence of PTGS in betalain biosynthesis in bougainvillea (Bougainvillea peruviana) ‘Thimma’, which produces bracts of three different color on the same plant, namely pink, white, and pink-white. This resembles the unstable anthocyanin pigmentation phenotype that is associated with PTGS, and hence we anticipated the presence of PTGS in the betalain biosynthetic pathway. To test this, we analysed pigments, gene expression, small RNAs, and transient overexpression. Our results demonstrated that PTGS of BpCYP76AD1, a gene encoding one of the betalain biosynthesis enzymes, is responsible for the loss of betalain biosynthesis in ‘Thimma’. Neither the genetic background nor DNA methylation in the BpCYP76AD1 sequence could explain the induction of PTGS, implying that another locus controls the unstable pigmentation. Our results indicate that naturally occurring PTGS contributes to the diversification of color patterns not only in anthocyanin biosynthesis but also in betalain biosynthesis.

Yellow color in dahlia flowers is conferred from chalcones, butein and isoliquiritigenin. The color intensity of yellow dahlia cultivars is diverse, but a detailed study on this has not yet been performed. In this study, we first identified structures of flavonoids by nuclear magnetic resonance imaging in ray florets of the red-white bicolor ‘Shukuhai’, which contains chalcones, flavones and anthocyanins. Four anthocyanins, four flavone derivatives, five isoliquiritigenin derivatives and five butein derivatives were identified. Among the identified compounds, butein 4'-malonylsophoroside is considered to be the final product for butein derivatives and the presence of chalcone 4'-glucosyltransferase, chalcone 4'-glucoside glucosyltransferase, and chalcone 4'-glucoside malonyltransferase for isoliquiritigenin and butein modification was predicted. Also, the biosynthetic pathway of butein and isoliquiritigenin derivatives in dahlia with butein 4'-malonylsophoroside as the final product was predicted from the identified compounds. Next, we used nine yellow cultivars and lines with different color intensities and analyzed the correlation between the b* value, an indicator of yellow color, and level of chalcones. There was no difference in the presence or absence of major peaks among the cultivars and lines. Peak area per fresh weight measured by HPLC was high in butein 4'-malonylglucoside, butein 4'-sophoroside and isoliquiritigenin 4'-malonylglucoside, suggesting these three compounds were accumulated abundantly. Among the identified chalcones, the highest correlation coefficient was detected between the b* value and butein 4'-malonylglucoside (r = 0.86), butein 4'-sophoroside (r = 0.82) or isoliquiritigenin 4'-malonylglucoside (r = 0.76). These results suggest that these three chalcones confer yellow color in dahlia ray florets. The findings in this study will contribute not only to efforts at breeding new yellow dahlia cultivars, but also to molecular breeding of yell

Anthocyanin in pepper is beneficial as a food antioxidant compound and as a pigment for ornamentals, while unexpected anthocyanin accumulation in fruit, known as black spots, reduces the commercial quality of some cultivars. Previous studies demonstrated that the Anthocyanin (A) locus determines the anthocyanin accumulation in pepper fruits, and an MYB transcription factor, CaMYBA, was found to be located near the A locus. However, the causal gene sequence of the A locus has not yet been identified. With progress regarding genome information in pepper, two other homologous MYB genes were found to be located near CaMYBA, and they are also considered to be candidate genes for the A locus. In this study, we attempted to identify the causal gene sequence of the A locus by performing linkage analysis, genomic sequence analysis, and gene expression analysis of the three candidate MYB genes. A crossing experiment between pigmented ‘Peruvian Purple’ and non-pigmented cultivars confirmed that anthocyanin accumulation in the pigmented cultivar was controlled by a single locus. Gene expression analysis demonstrated that a basic helix-loop-helix transcription factor, CaMYC, and CaMYBA were expressed abundantly in pigmented cultivars, but the other two MYB genes were not. Genotyping of the F2 population derived from the cross demonstrated that the anthocyanin accumulation phenotype was highly linked to CaMYBA, but not to CaMYC. The DNA sequence of CaMYBA in pigmented cultivars had an insertion of a 4.3 kb retrotransposable element LINE-1 in the first intron, but that of non-pigmented cultivars did not. No pigmented cultivar-specific sequence was found in the promoter region of CaMYBA. Therefore, it was suggested that CaMYBA, but not the other two homologous MYB genes, is the A locus gene, and insertion of LINE-1 in CaMYBA appeared to be important for the regulation of anthocyanin accumulation, although the mechanism by which the LINE-1 insertion induces CaMYBA expression is unkn

Main conclusion: 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.