Molecular characterization of mutations in white-flowered torenia plants

Metabolomic and Transcriptomic Analyses of Flavonoid Biosynthesis in Dendrobium devonianum Flowers

BACKGROUND

Dendrobium devonianum is a traditional Chinese medicinal herb with notable ornamental and medicinal value.

METHODS

In this study, transcriptomic and metabolomic approaches were employed to investigate gene expression and secondary metabolite changes during four developmental stages of D. devonianum flowers.

RESULTS

Metabolomic analysis identified 1186 distinct metabolites, with flavonoid compounds being the most abundant category (213 types). Transcriptomic analysis revealed 31 differentially expressed genes associated with flavonoid biosynthesis and flavonoid and flavonol biosynthesis pathways. Among these, key genes regulating flavonol synthesis, including F3H (Unigene0077194) and FLS (Unigene0062137), exhibited high expression levels in the early developmental stage (S1).

CONCLUSIONS

Flavonoids serve as the major active components in D. devonianum flowers, exhibiting a wide range of pharmacological properties. This study provides valuable insights into the molecular mechanisms driving flavonoid accumulation in D. devonianum, offering a foundation for further functional studies and applications in ornamental and medicinal plant research.

Genetic Transformation of Torenia fournieri L. with the Bacillus thuringiensis Cry1Ab Gene Confers Resistance to Mythimna separata (Walker)

Torenia fournieri L. is a popular ornamental plant in the genus Torenia, widely used in commercial landscaping, especially during the summer. Additionally, Torenia has served as a model ornamental plant in many studies exploring ornamental characteristics and pest control through genetic engineering. To date, no research has been reported on developing insect-resistant Torenia expressing genes from Bacillus thuringiensis (Bt). In this study, a recombinant vector carrying the Cry1Ab gene from Bt, pBI121-Cry1Ab, was constructed and transferred into T. fournieri via Agrobacterium tumefaciens-mediated transformation. A total of 13 shoots survived on the kanamycin selection medium, among which four putative transgenic lines, designated L1, L2, L7, and L11, were molecularly confirmed by PCR and Southern blot analysis, indicating successful integration of the Cry1Ab gene into the genomes of these lines. Quantitative real-time PCR and ELISA results further verified the successful expression of the Cry1Ab gene in the leaves of all four transgenic lines. Insect bioassay results demonstrated that all four transgenic lines showed strong resistance to the insect pest, Mythimna separata, with mortality rates ranging from 59.9% to 100.0%, in contrast to a larval mortality rate of 16.2% in the wild-type Torenia. Additionally, these transgenic lines significantly decreased in larval survival rates compared to those fed on wild-type plants. Furthermore, these transgenic lines activated superoxide dismutase (SOD) activity at 12 and 24 h, and catalase (CAT) activity at 72 h, while suppressing SOD activity at 72 h, and peroxidase (POD) activity over time. Our findings indicate that these transgenic lines exhibit high resistance to the insect pest and provide new insights into controlling insect pests in ornamental plants through genetic approaches.

Flower color modification in Torenia fournieri by genetic engineering of betacyanin pigments

BACKGROUND

Betalains are reddish and yellow pigments that accumulate in a few plant species of the order Caryophyllales. These pigments have antioxidant and medicinal properties and can be used as functional foods. They also enhance resistance to stress or disease in crops. Several plant species belonging to other orders have been genetically engineered to express betalain pigments. Betalains can also be used for flower color modification in ornamental plants, as they confer vivid colors, like red and yellow. To date, betalain engineering to modify the color of Torenia fournieri-or wishbone flower-a popular ornamental plant, has not been attempted.

RESULTS

We report the production of purple-reddish-flowered torenia plants from the purple torenia cultivar "Crown Violet."  Three betalain-biosynthetic genes encoding CYP76AD1, dihydroxyphenylalanine (DOPA) 4,5-dioxygenase (DOD), and cyclo-DOPA 5-O-glucosyltransferase (5GT) were constitutively ectopically expressed under the cauliflower mosaic virus (CaMV) 35S promoter, and their expression was confirmed by quantitative real-time PCR (qRT-PCR) analysis. The color traits, measured by spectrophotometric colorimeter and spectral absorbance of fresh petal extracts, revealed a successful flower color modification from purple to reddish. Red pigmentation was also observed in whole plants. LC-DAD-MS and HPLC analyses confirmed that the additional accumulated pigments were betacyanins-mainly betanin (betanidin 5-O-glucoside) and, to a lesser extent, isobetanin (isobetanidin 5-O-glucoside). The five endogenous anthocyanins in torenia flower petals were also detected.

CONCLUSIONS

This study demonstrates the possibility of foreign betacyanin accumulation in addition to native pigments in torenia, a popular garden bedding plant. To our knowledge, this is the first report presenting engineered expression of betalain pigments in the family Linderniaceae. Genetic engineering of betalains would be valuable in increasing the flower color variation in future breeding programs for torenia.

Functional Characterization of F3H Gene and Optimization of Dihydrokaempferol Biosynthesis in Saccharomyces cerevisiae

The 1092 bp F3H gene from Trapa bispinosa Roxb., which was named TbF3H, was cloned and it encodes 363 amino acids. Bioinformatic and phylogenetic tree analyses revealed the high homology of TbF3H with flavanone 3-hydroxylase from other plants. A functional analysis showed that TbF3H of Trapa bispinosa Roxb. encoded a functional flavanone 3-hydroxylase; it catalyzed the formation of dihydrokaempferol (DHK) from naringenin in S. cerevisiae. The promoter strengths were compared by fluorescence microscopy and flow cytometry detection of the fluorescence intensity of the reporter genes initiated by each constitutive promoter (FITC), and DHK production reached 216.7 mg/L by the promoter adjustment strategy and the optimization of fermentation conditions. The results presented in this study will contribute to elucidating DHK biosynthesis in Trapa bispinosa Roxb.

Molecular characterization of a flavanone 3-hydroxylase gene from citrus fruit reveals its crucial roles in anthocyanin accumulation

BACKGROUND

Flavanone 3-hydroxylase (F3H), a key enzyme in the flavonoid biosynthetic pathway, plays an important role in the regulation of flavonols and anthocyanidins accumulation. Citrus fruit is a rich source of flavonoids with varied flavonoid compositions among different varieties. To date, the study on F3H is limited in citrus, and its roles in regulating flavonoid accumulation in citrus fruit are still unclear.

RESULTS

In this study, we isolated a CitF3H from three different citrus varieties, Satsuma mandarin (Citrus unshiu Marc.), Ponkan mandarin (C. reticulata Blanco) and blood orange 'Moro' (C. sinensis Osbeck). Functional analysis showed that CitF3H encoded a functional flavanone 3-hydroxylase. It catalyzed the hydroxylation of naringenin to yield dihydrokaempferol, which was a precursor of anthocyanins in flavonoid biosynthetic pathway. In the juice sacs, CitF3H was differentially expressed among the three citrus varieties, and its expression level was positively correlated with the accumulation of anthocyanins during the ripening process. In the juice sacs of Satsuma mandarin and Ponkan mandarin the expression of CitF3H kept constant at an extremely low level, and no anthocyanin was accumulated during the ripening process. In contrast, the expression of CitF3H increased rapidly along with the accumulation of anthocyanin in the juice sacs of blood orange 'Moro' during the ripening process. In addition, we found that blue light irradiation was effective to up-regulate the expression of CitF3H and improve anthocyanin accumulation in the juice sacs of blood orange 'Moro' in vitro.

CONCLUSION

CitF3H was a key gene regulating anthocyanin accumulation in the juice sacs of citrus fruit. The results presented in this study will contribute to elucidating anthocyanin biosynthesis in citrus fruit, and provide new strategies to improve the nutritional and commercial values of citrus fruit.

Integrated metabolome and transcriptome analysis unveils novel pathway involved in the fruit coloration of Nitraria tangutorum Bobr

BACKGROUND

The desert shrub Nitraria tangutorum Bobr. is important for its resistance to salt and alkali in Northwest China. It is an ecologically important species in this region and provides edible and medicinal berries. This study showed a mutant of N. tangutorum (named Jincan, JC) that has a strong yellow pericarp vs red in a wild type (represented by NT).

RESULTS

In this study, the secondary metabolic and molecular mechanisms responsible for Nitraria fruit coloration were investigated using LC-MS-based widely targeted metabolomics and transcriptomics data. As a result of our study, 122 and 104 flavonoid metabolites were differentially expressed throughout the mature and transition stages between JC and NT, respectively. Furthermore, two cyanidin derivatives (cyanidin 3-O-glucoside and cyanidin-3-O-(2''-O-glucosyl) glucoside) and one pelargonidin derivative (pelargonidin-3-O-glucoside) were identified only in the NT phenotype. The functional genes F3H (flavanone 3-hydroxylase), F3'H (flavonoid 3'-hydroxylase) and UFGT (flavonoid 3-O-glucosyltransferase) and the transcription factors MYB, bHLH, NAC and bZIP were significantly downregulated in JC. Meanwhile, the activity of UFGT was extremely low in both periods of JC, with a five-fold higher enzymatic activity of UFGT in RT than in YT. In summary, due to the lack of catalysis of UGFT, yellow fruit of JC could not accumulate sufficient cyanidin and pelargonidin derivatives during fruit ripening.

CONCLUSION

Taken together, our data provide insights into the mechanism for the regulation of anthocyanin synthesis and N. tangutorum fruit coloration and provide a theoretical basis to develop new strategies for developing bioactive compounds from N. tangutorum fruits.

Stability of petal color polymorphism: the significance of anthocyanin accumulation in photosynthetic tissues

BACKGROUND

Anthocyanins are the primary source of colour in flowers and also accumulate in vegetative tissues, where they have multiple protective roles traditionally attributed to early compounds of the metabolic pathway (flavonols, flavones, etc.). Petal-specific loss of anthocyanins in petals allows plants to escape from the negative pleiotropic effects of flavonoid and anthocyanins loss in vegetative organs, where they perform a plethora of essential functions. Herein, we investigate the degree of pleiotropy at the biochemical scale in a pink-white flower colour polymorphism in the shore campion, Silene littorea. We report the frequencies of pink and white individuals across 21 populations and underlying biochemical profiles of three flower colour variants: anthocyanins present in all tissues (pink petals), petal-specific loss of anthocyanins (white petals), and loss of anthocyanins in all tissues (white petals).

RESULTS

Individuals lacking anthocyanins only in petals represent a stable polymorphism in two populations at the northern edge of the species range (mean frequency 8-21%). Whereas, individuals lacking anthocyanins in the whole plant were found across the species range, yet always at very low frequencies (< 1%). Biochemically, the flavonoids detected were anthocyanins and flavones; in pigmented individuals, concentrations of flavones were 14-56× higher than anthocyanins across tissues with differences of > 100× detected in leaves. Loss of anthocyanin pigmentation, either in petals or in the whole plant, does not influence the ability of these phenotypes to synthesize flavones, and this pattern was congruent among all sampled populations.

CONCLUSIONS

We found that all colour variants showed similar flavone profiles, either in petals or in the whole plant, and only the flower colour variant with anthocyanins in photosynthetic tissues persists as a stable flower colour polymorphism. These findings suggest that anthocyanins in photosynthetic tissues, not flavonoid intermediates, are the targets of non-pollinator mediated selection.

Application of the CRISPR/Cas9 system for modification of flower color in Torenia fournieri

BACKGROUND

CRISPR/Cas9 technology is one of the most powerful and useful tools for genome editing in various living organisms. In higher plants, the system has been widely exploited not only for basic research, such as gene functional analysis, but also for applied research such as crop breeding. Although the CRISPR/Cas9 system has been used to induce mutations in genes involved in various plant developmental processes, few studies have been performed to modify the color of ornamental flowers. We therefore attempted to use this system to modify flower color in the model plant torenia (Torenia fournieri L.).

RESULTS

We attempted to induce mutations in the torenia flavanone 3-hydroxylase (F3H) gene, which encodes a key enzyme involved in flavonoid biosynthesis. Application of the CRISPR/Cas9 system successfully generated pale blue (almost white) flowers at a high frequency (ca. 80% of regenerated lines) in transgenic torenia T0 plants. Sequence analysis of PCR amplicons by Sanger and next-generation sequencing revealed the occurrence of mutations such as base substitutions and insertions/deletions in the F3H target sequence, thus indicating that the obtained phenotype was induced by the targeted mutagenesis of the endogenous F3H gene.

CONCLUSIONS

These results clearly demonstrate that flower color modification by genome editing with the CRISPR/Cas9 system is easily and efficiently achievable. Our findings further indicate that this system may be useful for future research on flower pigmentation and/or functional analyses of additional genes in torenia.

The CYCLOIDEA-RADIALIS module regulates petal shape and pigmentation, leading to bilateral corolla symmetry in Torenia fournieri (Linderniaceae)

The diverse pigmentation patterns of flower corollas probably result from pollinator-mediated selection. Previous studies demonstrated that R2R3-MYB factors may have been recruited in the regulation of corolla pigmentation. However, how R2R3-MYBs became so diverse in their regulation of different pigmentation patterns remains unclear. Here, we studied a Lamiales species, Torenia fournieri, which has elaborate zygomorphic flowers with dorsal-ventral asymmetries in corolla pigmentation. We found recent gene duplication events in CYCLOIDEA-like (CYC-like) and RADIALIS-like (RAD-like) genes, and functionally analyzed three dorsal-specific expression factors: TfCYC1, TfCYC2, and TfRAD1. We found that the CYC-RAD module coordinates petal shape and corolla pigmentation, as ectopic expression of TfCYC2 or TfRAD1 disrupted the asymmetric corolla pigmentation pattern and produced strongly dorsalized flowers. Dorsal petal identity was lost when TfCYC2 was down-regulated or when TfRAD1 was knocked out. In T. fournieri, the diversified CYC and RAD genes have evolved regulatory loops, and TfCYC2 binds directly to the regulatory regions of an R2R3-MYB factor gene, TfMYB1, which might lead to its asymmetric expression and ultimately establish the asymmetric pigmentation pattern. These findings support the existence of a regulatory module that integrates dorsal-ventral patterning and asymmetric corolla pigmentation in T. fournieri.

Molecular characterization of flavanone 3-hydroxylase gene and flavonoid accumulation in two chemotyped safflower lines in response to methyl jasmonate stimulation

BACKGROUND

Among secondary metabolites, flavonoids are particularly crucial for plant growth, development, and reproduction, as well as beneficial for maintenance of human health. As a flowering plant, safflower has synthesized a striking variety of flavonoids with various pharmacologic properties. However, far less research has been carried out on the genes involved in the biosynthetic pathways that generate these amazing flavonoids, especially characterized quinochalcones. In this study, we first cloned and investigated the participation of a presumed flavanone 3-hydroxylase gene (F3H) from safflower (CtF3H) in a flavonoid biosynthetic pathway.

RESULTS

Bioinformation analysis showed that CtF3H shared high conserved residues and confidence with F3H from other plants. Subcellular localization uncovered the nuclear and cytosol localization of CtF3H in onion epidermal cells. The functional expressions of CtF3H in Escherichia coli BL21(DE3)pLysS cells in the pMAL-C5x vector led to the production of dihydrokaempferol when naringenin was the substrate. Furthermore, the transcriptome expression of CtF3H showed a diametrically opposed expression pattern in a quinochalcone-type safflower line (with orange-yellow flowers) and a flavonol-type safflower line (with white flowers) under external stimulation by methyl jasmonate (MeJA), which has been identified as an elicitor of flavonoid metabolites. Further metabolite analysis showed the increasing tendency of quinochalcones and flavonols, such as hydroxysafflor yellow A, kaempferol-3-O-β-D-glucoside, kaempferol-3-O-β-rutinoside, rutin, carthamin, and luteolin, in the quinochalcone-type safflower line. Also, the accumulation of kaempferol-3-O-β-rutinoside and kaempferol-3-O-β-D-glucoside in flavonols-typed safflower line showed enhanced accumulation pattern after MeJA treatment. However, other flavonols, such as kaempferol, dihydrokaempferol and quercetin-3-O-β-D-glucoside, in flavonols-typed safflower line presented down accumulation respond to MeJA stimulus.

CONCLUSIONS

Our results showed that the high expression of CtF3H in quinochalcone-type safflower line was associated with the accumulation of both quinochalcones and flavonols, whereas its low expression did not affect the increased accumulation of glycosylated derivatives (kaempferol-3-O-β-rutinoside and rutin) in flavonols-typed safflower line but affect the upstream precursors (D-phenylalanine, dihydrokaempferol, kaempferol), which partly revealed the function of CtF3H in different phenotypes and chemotypes of safflower lines.

Assembly of the draft genome of buckwheat and its applications in identifying agronomically useful genes

Buckwheat (Fagopyrum esculentum Moench; 2n = 2x = 16) is a nutritionally dense annual crop widely grown in temperate zones. To accelerate molecular breeding programmes of this important crop, we generated a draft assembly of the buckwheat genome using short reads obtained by next-generation sequencing (NGS), and constructed the Buckwheat Genome DataBase. After assembling short reads, we determined 387,594 scaffolds as the draft genome sequence (FES_r1.0). The total length of FES_r1.0 was 1,177,687,305 bp, and the N50 of the scaffolds was 25,109 bp. Gene prediction analysis revealed 286,768 coding sequences (CDSs; FES_r1.0_cds) including those related to transposable elements. The total length of FES_r1.0_cds was 212,917,911 bp, and the N50 was 1,101 bp. Of these, the functions of 35,816 CDSs excluding those for transposable elements were annotated by BLAST analysis. To demonstrate the utility of the database, we conducted several test analyses using BLAST and keyword searches. Furthermore, we used the draft genome as a reference sequence for NGS-based markers, and successfully identified novel candidate genes controlling heteromorphic self-incompatibility of buckwheat. The database and draft genome sequence provide a valuable resource that can be used in efforts to develop buckwheat cultivars with superior agronomic traits.

Transcriptome and Biochemical Analysis of a Flower Color Polymorphism in Silene littorea (Caryophyllaceae)

Flower color polymorphisms are widely used as model traits from genetics to ecology, yet determining the biochemical and molecular basis can be challenging. Anthocyanin-based flower color variations can be caused by at least 12 structural and three regulatory genes in the anthocyanin biosynthetic pathway (ABP). We use mRNA-Seq to simultaneously sequence and estimate expression of these candidate genes in nine samples of Silene littorea representing three color morphs (dark pink, light pink and white) across three developmental stages in hopes of identifying the cause of flower color variation. We identified 29 putative paralogs for the 15 candidate genes in the ABP. We assembled complete coding sequences for 16 structural loci and nine of ten regulatory loci. Among these 29 putative paralogs, we identified 622 SNPs, yet only nine synonymous SNPs in Ans had allele frequencies that differentiated pigmented petals (dark pink and light pink) from white petals. These Ans allele frequency differences were further investigated with an expanded sequencing survey of 38 individuals, yet no SNPs consistently differentiated the color morphs. We also found one locus, F3h1, with strong differential expression between pigmented and white samples (>42x). This may be caused by decreased expression of Myb1a in white petal buds. Myb1a in S. littorea is a regulatory locus closely related to Subgroup 7 Mybs known to regulate F3h and other loci in the first half of the ABP in model species. We then compare the mRNA-Seq results with petal biochemistry which revealed cyanidin as the primary anthocyanin and five flavonoid intermediates. Concentrations of three of the flavonoid intermediates were significantly lower in white petals than in pigmented petals (rutin, quercetin and isovitexin). The biochemistry results for rutin, quercetin, luteolin and apigenin are consistent with the transcriptome results suggesting a blockage at F3h, possibly caused by downregulation of Myb1a.

Transcriptome sequencing of purple petal spot region in tree peony reveals differentially expressed anthocyanin structural genes

The pigmented cells in defined region of a petal constitute the petal spots. Petal spots attract pollinators and are found in many angiosperm families. Several cultivars of tree peony contain a single red or purple spot at the base of petal that makes the flower more attractive for the ornamental market. So far, the understanding of the molecular mechanism of spot formation is inadequate. In this study, we sequenced the transcriptome of the purple spot and the white non-spot of tree peony flower. We assembled and annotated 67,892 unigenes. Comparative analyses of the two transcriptomes showed 1,573 differentially expressed genes, among which 933 were up-regulated, and 640 were down-regulated in the purple spot. Subsequently, we examined four anthocyanin structural genes, including PsCHS, PsF3'H, PsDFR, and PsANS, which expressed at a significantly higher level in the purple spot than in the white non-spot. We further validated the digital expression data using quantitative real-time PCR. Our result uncovered transcriptome variance between the spot and non-spot of tree peony flower, and revealed that the co-expression of four anthocyanin structural genes was responsible for spot pigment in tree peony. The data will further help to unravel the genetic mechanism of peony flower spot formation.

Ecological transition predictably associated with gene degeneration

Gene degeneration or loss can significantly contribute to phenotypic diversification, but may generate genetic constraints on future evolutionary trajectories, potentially restricting phenotypic reversal. Such constraints may manifest as directional evolutionary trends when parallel phenotypic shifts consistently involve gene degeneration or loss. Here, we demonstrate that widespread parallel evolution in Penstemon from blue to red flowers predictably involves the functional inactivation and degeneration of the enzyme flavonoid 3',5'-hydroxylase (F3'5'H), an anthocyanin pathway enzyme required for the production of blue floral pigments. Other types of genetic mutations do not consistently accompany this phenotypic shift. This pattern may be driven by the relatively large mutational target size of degenerative mutations to this locus and the apparent lack of associated pleiotropic effects. The consistent degeneration of F3'5'H may provide a mechanistic explanation for the observed asymmetry in the direction of flower color evolution in Penstemon: Blue to red transitions are common, but reverse transitions have not been observed. Although phenotypic shifts in this system are likely driven by natural selection, internal constraints may generate predictable genetic outcomes and may restrict future evolutionary trajectories.