MYB and bHLH transcription factor transgenes increase anthocyanin pigmentation in petunia and lisianthus plants, and the petunia phenotypes are strongly enhanced under field conditions

Comprehensive genomic analysis of SmbHLH genes and the role of SmbHLH93 in eggplant anthocyanin biosynthesis

KEY MESSAGE

SmbHLH93can activate the expression of SmCHS, SmANS, SmDFR and SmF3H.Overexpression of SmbHLH93promotes anthocyanin biosynthesis. SmbHLH93can interact with SmMYB1 to promote anthocyanin accumulation. As an outstanding source of anthocyanins, eggplant (Solanum melongena L.) is extremely beneficial for human health. In the process of anthocyanin biosynthesis in eggplant, the basic helix-loop-helix (bHLH) transcription factor family plays a crucial role. However, the bHLH gene family is extensive, making it difficult to systematically screen and analyze their functions using conventional methods. We studied the phylogeny, gene structure, conserved motifs, promoter element, and chromosomal location of the 166 SmbHLH genes in the recently released eggplant genome. Through the analysis of transcriptomic data of eggplant peel treated with light, it was found that SmbHLH93 was the most responsive to light among those of unknown function. Additionally, it was discovered that SmbHLH93 plays a positive regulatory role in anthocyanin synthesis through dual-luciferase reporter assay(dual-LUC) and genetic transformation in Arabidopsis (Arabidopsis thaliana). Furthermore, experiments involving yeast two-hybrid (Y2H), luciferase complementation assay (Split-LUC), and tobacco transient transformation demonstrated that SmbHLH93 has the ability to interact with SmMYB1 in order to enhance anthocyanin accumulation. This study will serve as a foundation for exploring the role of SmbHLH transcription factors in anthocyanin biosynthesis in the future.

Transcriptomic and Metabolic Analysis Reveals Genes and Pathways Associated with Flesh Pigmentation in Potato (Solanum tuberosum) Tubers

Anthocyanins, flavonoid pigments, are responsible for the purple and red hues in potato tubers. This study analyzed tubers from four potato cultivars-red RR, purple HJG, yellow QS9, and white JZS8-to elucidate the genetic mechanisms underlying tuber pigmentation. Our transcriptomic analysis identified over 2400 differentially expressed genes between these varieties. Notably, genes within the flavonoid biosynthesis pathway were enriched in HJG and RR compared to the non-pigmented JZS8, correlating with their higher levels of anthocyanin precursors and related substances. Hierarchical clustering revealed inverse expression patterns for the key genes involved in anthocyanin metabolism between pigmented and non-pigmented varieties. Among these, several MYB transcription factors displayed strong co-expression with anthocyanin biosynthetic genes, suggesting a regulatory role. Specifically, the expression of 16 MYB genes was validated using qRT-PCR to be markedly higher in pigmented HJG and RR versus JZS8, suggesting that these MYB genes might be involved in tuber pigmentation. This study comprehensively analyzed the transcriptome of diverse potato cultivars, highlighting specific genes and metabolic pathways involved in tuber pigmentation. These findings provide potential molecular targets for breeding programs focused on enhancing tuber color.

Functional identification of DNA demethylase gene CaROS1 in pepper (Capsicum annuum L.) involved in salt stress

Pepper, which is a widely cultivated important vegetable, is sensitive to salt stress, and the continuous intensification of soil salinization has affected pepper production worldwide. However, genes confer to salt tolerance are rarely been cloned in pepper. Since the REPRESSOR OF SILENCING 1 (ROS1) is a DNA demethylase that plays a crucial regulatory role in plants in response to various abiotic stresses, including salt stress. We cloned a ROS1 gene in pepper, named CaROS1 (LOC107843637). Bioinformatic analysis showed that the CaROS1 protein contains the HhH-GPD glycosylase and RRM_DME domains. qRT-PCR analyses showed that the CaROS1 was highly expressed in young and mature fruits of pepper and rapidly induced by salt stress. Functional characterization of the CaROS1 was performed by gene silencing in pepper and overexpressing in tobacco, revealed that the CaROS1 positively regulates salt tolerance ability. More detailly, CaROS1-silenced pepper were more sensitive to salt stress, and their ROS levels, relative conductivity, and malondialdehyde content were significantly higher in leaves than those of the control plants. Besides, CaROS1-overexpressing tobacco plants were more tolerant to salt stress, with a higher relative water content, total chlorophyll content, and antioxidant enzyme activity in leaves compared to those of WT plants during salt stress. These results revealed the CaROS1 dose play a role in salt stress response, providing the theoretical basis for salt tolerance genetic engineering breeding in pepper.

Advancing understanding of Ficus carica: a comprehensive genomic analysis reveals evolutionary patterns and metabolic pathway insights

Ficus carica L. (dioecious), the most significant commercial species in the genus Ficus, which has been cultivated for more than 11,000 years and was one of the first species to be domesticated. Herein, we reported the most comprehensive F. carica genome currently. The contig N50 of the Orphan fig was 9.78 Mb, and genome size was 366.34 Mb with 13 chromosomes. Based on the high-quality genome, we discovered that F. carica diverged from Ficus microcarpa ~34 MYA, and a WGD event took place about 2─3 MYA. Throughout the evolutionary history of F. carica, chromosomes 2, 8, and 10 had experienced chromosome recombination, while chromosome 3 saw a fusion and fission. It is worth proposing that the chromosome 9 experienced both inversion and translocation, which facilitated the emergence of the F. carica as a new species. And the selections of F. carica for the genes of recombination chromosomal fragment are compatible with their goal of domestication. In addition, we found that the F. carica has the FhAG2 gene, but there are structural deletions and positional jumps. This gene is thought to replace the one needed for female common type F. carica to be pollinated. Subsequently, we conducted genomic, transcriptomic, and metabolomic analysis to demonstrate significant differences in the expression of CHS among different varieties of F. carica. The CHS playing an important role in the anthocyanin metabolism pathway of F. carica. Moreover, the CHS gene of F. carica has a different evolutionary trend compared to other Ficus species. These high-quality genome assembly, transcriptomic, and metabolomic resources further enrich F. carica genomics and provide insights for studying the chromosomes evolution, sexual system, and color characteristics of Ficus.

Comparative transcriptome analysis reveals an insight into the candidate genes involved in anthocyanin and scent volatiles biosynthesis in colour changing flowers of Combretum indicum

Combretum indicum is a widely cultivated ornamental species displaying the distinct phenomenon of floral colour change. Flowers display a gradual colour change from white to red, attributed to increased cyanidin 3-O glucoside in petal tissues. The differently coloured flowers also emanate a complex blend of VOCs with trans-linalool oxide (furanoid) as the major compound in the emission profile. To understand molecular mechanisms regulating floral colour shifts and scent biosynthesis, we performed Illumina transcriptome sequencing, including de novo assembly and functional annotation, for the two stages of floral maturation (white and red). Homology analysis with functional classification identified 84 and 42 candidate genes associated with pigment and scent biosynthesis, respectively. Genes encoding transcription factors, such as MYB, ERF, WD40, WRKY, NAC, bHLH and bZIP, that play critical roles in regulating specialized metabolism were also identified in the transcriptome data. Differences in expression of genes were consistent with accumulation patterns of anthocyanins in the two different flower colours. A clear upregulation of flavonoid biosynthesis genes in red flower tissue is associated with increased pigment content. RT-qPCR-based expression analyses gave results consistent with the RNA-Seq data, suggesting the sequencing data are consistent and reliable. This study presents the first report of genetic information for C. indicum. Gene sequences generated from RNA-Seq, along with candidate genes identified by pathway mapping and their expression profiles, provide a valuable resource for subsequent studies towards molecular understanding of specialized metabolism in C. indicum flowers.

Purple stem Brassica napus exhibits higher photosynthetic efficiency, antioxidant potential and anthocyanin biosynthesis related genes expression against drought stress

Purple-stem Brassica napus (B. napus) is a phenotype with unique color because of its high anthocyanins content. Anthocyanins are naturally occurring plant pigments that have antioxidants activity and play important role in plant defense against abiotic and biotic stresses. In the present study, drought induced effects on plants were investigated in hydroponically grown seedlings of green stem (GS) and purple stem (PS) genotypes of B. napus. The results of this study showed that the major function of anthocyanins accumulation during drought was to enhance the antioxidant capability and stress tolerance in B. napus plants. Our results showed that drought significantly inhibited the plant growth in terms of decreased biomass accumulation in both genotypes, although marked decline was observed in GS genotype. The reduction in photosynthetic attributes was more noticeable in the GS genotype, whereas the PS genotype showed better performance under drought stress. Under stressful conditions, both the genotype showed excessive accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as higher levels of antioxidant enzymes activities. Under drought conditions, the GS genotype showed apparent damages on chloroplast deformation like in thylakoid membrane and grana structural distortion and fewer starch grains and bigger plastoglobuli. Moreover, during drought stress, the PS genotype exhibited maximum expression levels of anthocyanins biosynthesis genes and antioxidant enzymes accompanied by higher stress tolerance relative to GS genotype. Based on these findings, it can be concluded that GS genotype found more sensitive to drought stress than the PS genotype. Furthermore this research paper also provides practical guidance for plant biologists who are developing stress-tolerant crops by using anthocyanin biosynthesis or regulatory genes.

Systems biology-based analysis indicates that PHO1;H10 positively modulates high light-induced anthocyanin biosynthesis in Arabidopsis leaves

Arabidopsis PHO1;H10 is a member of the PHO1 gene family with SPX and EXS domains, and its functions remain largely unknown. As shown in PCSD database, the upstream region of PHO1;H10 gene is in the active chromatin states, with high DHS accessibility and binding sites of multiple transcription factors, especially ABI5, SPCH and HY5. Co-expression network and data-mining analyses showed PHO1;H10 and co-expression genes were with activation under high light stress. We did wet-lab experiments, and found that the detached leaves of PHO1;H10 overexpression lines accumulated more anthocyanin than those of WT and mutant under high light treatment. RNA-seq results showed overexpression of PHO1;H10 up-regulated many anthocyanin biosynthetic genes. The GSEA analysis result showed that the functional module related to anthocyanin pathway was significantly enriched. In summary, we conducted systems biology approach, combining dry- and wet-lab analyses, and discovered that PHO1;H10 might play an essential role during modulating high light-induced anthocyanin accumulation in the Arabidopsis detached leaves.

Improving the anthocyanin accumulation of hypocotyls in radish sprouts by hemin-induced NO

BACKGROUND

The health benefits of anthocyanins impel researchers and food producers to explorer new methods to increase anthocyanin contents in plant foods. Our previous studies revealed a positive role of nitric oxide (NO) in anthocyanin accumulation in radish (Raphanus sativus L.) sprouts. The application of hemin, an inducer of heme oxygenase-1 (HO-1), can effectively elevate NO production in vivo. Hemin treatment also improves plant growth and stress tolerance. This study is aimed to assess the effects of hemin treatment on anthocyanin production in radish sprouts, and to investigate whether NO signalling is involved in this process.

RESULTS

The application of hemin significantly up regulated the expressions of many anthocyanins biosynthesis related structure and regulatory genes, leading to increased anthocyanins accumulation in radish hypocotyls. Hemin treatment also raised NO contents in radish sprouts, probably through enhancing nitrate reductase (NR) activity and Nitric Oxide-Associated 1 (NOA1) expression. Comparing the effects of Zinc Protoporphyrin (ZnPP, HO-1 activity inhibitor), Sodium Nitroprusside (SNP, NO donor) and carboxy-PTIO (cPTIO, NO-scavenger) on anthocyanin and NO production, a positive role of NO signalling has been revealed in hemin-derived anthocyanin accumulation. A positive feedback loop between HO-1 and NO may be involved in regulating this process.

CONCLUSIONS

Hemin induced anthocyanin accumulation in radish sprouts through HO-1 and NO signalling network.

Chili Pepper AN2 (CaAN2): A Visible Selection Marker for Nondestructive Monitoring of Transgenic Plants

Selecting transformed plants is generally time consuming and laborious. To develop a method for transgenic plant selection without the need for antibiotics or herbicides, we evaluated the suitability of the R2R3 MYB transcription factor gene CaAN2 from purple chili pepper (Capsicum annuum) for use as a visible selection marker. CaAN2 positively regulates anthocyanin biosynthesis. Transient expression assays in tobacco (Nicotiana tabacum) leaves revealed that CaAN2 actively induced sufficient pigment accumulation for easy detection without the need for a basic helix-loop-helix (bHLH) protein as a cofactor; similar results were obtained for tobacco leaves transiently co-expressing the anthocyanin biosynthesis regulators bHLH B-Peru from maize and R2R3 MYB mPAP1D from Arabidopsis. Tobacco plants harboring CaAN2 were readily selected based on their red color at the shoot regeneration stage due to anthocyanin accumulation without the need to impose selective pressure from herbicides. Transgenic tobacco plants harboring CaAN2 showed strong pigment accumulation throughout the plant body. The ectopic expression of CaAN2 dramatically promoted the transcription of anthocyanin biosynthetic genes as well as regulators of this process. The red coloration of tobacco plants harboring CaAN2 was stably transferred to the next generation. Therefore, anthocyanin accumulation due to CaAN2 expression is a useful visible trait for stable transformation, representing an excellent alternative selection system for transgenic plants.

CRISPR/Cas9-mediated targeted mutation reveals a role for AN4 rather than DPL in regulating venation formation in the corolla tube of Petunia hybrida

Venation is a common anthocyanin pattern displayed in flowers that confers important ornamental traits to plants. An anthocyanin-related R2R3-MYB transcription factor, DPL, has been proposed to regulate corolla tube venation in petunia plants. Here, however, we provide evidence redefining the role of DPL in petunia. A CRISPR/Cas9-mediated mutation of DPL resulted in the absence of the vein-associated anthocyanin pattern above the abaxial surface of the flower bud, but not corolla tube venation, thus indicating that DPL did not regulate the formation of corolla tube venation. Alternately, quantitative real-time PCR analysis demonstrated that the spatiotemporal expression pattern of another R2R3-MYB gene, AN4, coincided with the formation of corolla tube venation in petunia. Furthermore, overexpression of AN4 promoted anthocyanin accumulation by increasing the expression of anthocyanin biosynthesis genes. CRISPR/Cas9-mediated mutation of AN4 led to an absence of corolla tube venation, suggesting that this gene in fact determines this key plant trait. Taken together, the results presented here redefine the prime regulator of corolla tube venation, paving the way for further studies on the molecular mechanisms underlying the various venation patterns in petunia.

Increased substrate availability reveals the potential of scentless lisianthus flowers in producing fragrant benzenoid-phenylpropanoids

Lisianthus (Eustoma grandiflorum), a leading plant in the cut flower industry, is scentless. Here we show that lisianthus flowers have potential to produce several fragrant benzenoid-phenylpropanoids when substrate availability is not limited. To enable hyperaccumulation of substrates for the production of volatile benzenoid-phenylpropanoids, lisianthus commercial hybrid "Excalibur Pink" was transformed via floral dipping with a feedback-insensitive Escherichia coli DAHP synthase (AroG*) and Clarkia breweri benzyl alcohol acetyltransferase (BEAT), under constitutive promoters. The T1 progeny of "Excalibur Pink" plants segregated into four visual phenotypes, with pink or white colored petals and multiple or single petal layers. Interestingly, transformation with AroG* and BEAT caused no significant effect in the pigment composition among phenotypes, but did increase the levels of down-stream fragrant volatile benzenoids. All the transgenic lines exclusively accumulated methyl benzoate, a fragrant benzenoid, either in their petals or leaves. Furthermore, feeding with benzyl alcohol resulted in the accumulation of two novel benzenoids, benzyl acetate (the product of BEAT) and benzoate, as well as a dramatic increase in the concentrations of additional benzenoid-phenylpropanoid volatiles. Presumably, the degree of benzaldehyde overproduction after benzyl alcohol feeding in both leaves and flowers revealed their reverse conversion in lisianthus plants. These findings demonstrate the concealed capability of lisianthus plants to produce a wide array of fragrant benzenoid-phenylpropanoids, given high substrate concentrations, which could in turn open opportunities for future scent engineering.

Cyanidin based anthocyanin biosynthesis in orange carrot is restored by expression of AmRosea1 and AmDelila, MYB and bHLH transcription factors

The simultaneous expression of AmRosea1 and AmDelila transcription factors from snapdragon can activate the anthocyanin pathway in orange carrots, leading to the synthesis and accumulation of anthocyanins in the taproots. Anthocyanins are phenolic compounds produced in various parts of plants. They are used as natural food dyes and are reported as beneficial antioxidants for humans. Black carrot is an important source for anthocyanins; however, the reason for the lack of anthocyanin production in the orange carrot is unknown. Anthocyanins are synthesized by a specific branch of the phenylpropanoid pathway that has previously been reported to be activated by a triad of R2R3-MYB, basic helix-loop helix (bHLH) and WD40 transcription factors (TFs). In the current study, orange carrots were turned purple by simultaneous expression of R2R3-MYB and bHLH TFs, i.e. AmRosea1 and AmDelila from snapdragon (Antirrhinum majus). Simultaneous transgenic expression of the TFs under a constitutive promoter in the orange carrot cultivar 'Danvers 126' lead to consistent upregulation of anthocyanin-related biosynthetic genes and significant accumulation of anthocyanins in leaves, stems and taproots. Highest overall content of soluble anthocyanins in the taproot among the transformants amounted to 44.38 mg g^-1 dry weight. The anthocyanin profile of the transformants were significantly different from the profile in the reference black carrot 'Deep Purple'. The main anthocyanins present in the transformed taproots were cyanidin 3-xylosyl(sinapoylglucosyl)galactoside, whereas the main anthocyanin present in Deep Purple was cyanidin 3-xylosyl(feruloylglucosyl)galactoside. This study confirms the presence of the necessary biosynthetic genes in orange carrots for production of anthocyanins and demonstrates the absence of suitable R2R3-MYB and bHLH TFs for stimulating anthocyanin biosynthesis in the orange carrot.

The control of red colour by a family of MYB transcription factors in octoploid strawberry (Fragaria × ananassa) fruits

Octoploid strawberry (Fragaria × ananassa Duch.) is a model plant for research and one of the most important non-climacteric fruit crops throughout the world. The associations between regulatory networks and metabolite composition were explored for one of the most critical agricultural properties in octoploid strawberry, fruit colour. Differences in the levels of flavonoids are due to the differences in the expression of structural and regulatory genes involved in flavonoid biosynthesis. The molecular mechanisms underlying differences in fruit colour were compared between red and white octoploid strawberry varieties. FaMYB genes had combinatorial effects in determining the red colour of fruit through the regulation of flavonoid biosynthesis in response to the increase in endogenous ABA at the final stage of fruit development. Analysis of alleles of FaMYB10 and FaMYB1 in red and white strawberry varieties led to the discovery of a white-specific variant allele of FaMYB10, FaMYB10-2. Its coding sequence possessed an ACTTATAC insertion in the genomic region encoding the C-terminus of the protein. This insertion introduced a predicted premature termination codon, which suggested the loss of intact FaMYB10 protein playing a critical role in the loss of red colour in white octoploid strawberry.

MYB94 and MYB96 additively inhibit callus formation via directly repressing LBD29 expression in Arabidopsis thaliana

Plant somatic cells can be reprogrammed during in vitro culture. Callus induction is the initial step of a typical plant regeneration system. Recent studies showed that auxin-induced callus formation in multiple organs occurs from the pericycle or pericycle-like cells via a root developmental pathway. However, the molecular control of callus formation is largely unknown. Here, two MYB transcription factors, MYB94 and MYB96, were shown to play negative roles in auxin-induced callus formation in Arabidopsis. MYB94 and MYB96 were expressed in the newly formed callus. myb96, myb94, and myb94 myb96 generated more calli than the WT, with myb94 myb96 producing the most. MYB94 and MYB96 repressed expression of LATERAL ORGAN BOUNDARIES-DOMAIN 29 (LBD29) via directly binding to the gene's promoter. The loss of function of LBD29 partly rescued the callus formation defect of myb94 myb96. Our findings found MYB94 and MYB96 to be important repressors of callus formation and MYB94/96-LBD29 as a new regulatory pathway acting in parallel with ARF7/19-LBDs' pathway to modulate in vitro callus formation.

Overview and detectability of the genetic modifications in ornamental plants

The market of ornamental plants is extremely competitive, and for many species genetic engineering can be used to introduce original traits of high commercial interest. However, very few genetically modified (GM) ornamental varieties have reached the market so far. Indeed, the authorization process required for such plants has a strong impact on the profitability of the development of such products. Considering the numerous scientific studies using genetic modification on ornamental species of interest, a lot of transformed material has been produced, could be of commercial interest and could therefore be unintentionally released on the market. The unintentional use of GM petunia in breeding programs has indeed recently been observed. This review lists scientific publications using GM ornamental plants and tries to identify whether these plants could be detected by molecular biology tools commonly used by control laboratories.

Ectopic Expression of PAP1 Leads to Anthocyanin Accumulation and Novel Floral Color in Genetically Engineered Goldenrod (Solidago canadensis L.)

Floral pigmentation is of major importance to the ornamental industry, which is constantly searching for cultivars with novel colors. Goldenrod (Solidago canadensis) has monochromatic yellow carotenoid-containing flowers that cannot be modified using classical breeding approaches due to a limited gene pool. To generate Solidago with novel colors through metabolic engineering, we first developed a procedure for its regeneration and transformation. Applicability of different cytokinins for adventitious regeneration was examined in the commercial cv. Tara, with zeatin yielding higher efficiency than 6-benzylaminopurine or thidiazuron. A comparison of regeneration of commercial cvs. Tara, Golden Glory and Ivory Glory revealed Tara to be the most potent, with an efficiency of 86% (number of shoots per 100 leaf explants). Agrobacterium-based transformation efficiency was highest for cv. Golden Glory (5 independent transgenic shoots per 100 explants) based on kanamycin selection and the GUS reporter gene. In an attempt to promote anthocyanin biosynthesis, we generated transgenic Solidago expressing snapdragon (Antirrhinum majus) Rosea1 and Delila, as well as Arabidopsis thaliana PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) transcription factors. Transgenic cv. Golden Glory expressing cauliflower mosaic virus 35S-driven PAP1 generated red flowers that accumulated delphinidin and its methylated derivatives, as compared to control yellow flowers in the GUS-expressing plants. The protocol described here allows efficient engineering of Solidago for novel coloration and improved agricultural traits.

Enhanced Salt Tolerance of Rhizobia-inoculated Soybean Correlates with Decreased Phosphorylation of the Transcription Factor GmMYB183 and Altered Flavonoid Biosynthesis

Soybean (Glycine max (L.) Merrill) is an important component of the human diet and animal feed, but soybean production is limited by abiotic stresses especially salinity. We recently found that rhizobia inoculation enhances soybean tolerance to salt stress, but the underlying mechanisms are unaddressed. Here, we used quantitative phosphoproteomic and metabonomic approaches to identify changes in phosphoproteins and metabolites in soybean roots treated with rhizobia inoculation and salt. Results revealed differential regulation of 800 phosphopeptides, at least 32 of these phosphoproteins or their homologous were reported be involved in flavonoid synthesis or trafficking, and 27 out of 32 are transcription factors. We surveyed the functional impacts of all these 27 transcription factors by expressing their phospho-mimetic/ablative mutants in the roots of composite soybean plants and found that phosphorylation of GmMYB183 could affect the salt tolerance of the transgenic roots. Using data mining, ChIP and EMSA, we found that GmMYB183 binds to the promoter of the soybean GmCYP81E11 gene encoding for a Cytochrome P450 monooxygenase which contributes to the accumulation of ononin, a monohydroxy B-ring flavonoid that negatively regulates soybean tolerance to salinity. Phosphorylation of GmMYB183 was inhibited by rhizobia inoculation; overexpression of GmMYB183 enhanced the expression of GmCYP81E11 and rendered salt sensitivity to the transgenic roots; plants deficient in GmMYB183 function are more tolerant to salt stress as compared with wild-type soybean plants, these results correlate with the transcriptional induction of GmCYP81E11 by GmMYB183 and the subsequent accumulation of ononin. Our findings provide molecular insights into how rhizobia enhance salt tolerance of soybean plants.

A novel R2R3-MYB from grape hyacinth, MaMybA, which is different from MaAN2, confers intense and magenta anthocyanin pigmentation in tobacco

BACKGROUND

The primary pigments in flowers are anthocyanins, the biosynthesis of which is mainly regulated by R2R3-MYBs. Muscari armeniacum is an ornamental garden plant with deep cobalt blue flowers containing delphinidin-based anthocyanins. An anthocyanin-related R2R3-MYB MaAN2 has previously been identified in M. armeniacum flowers; here, we also characterized a novel R2R3-MYB MaMybA, to determine its function and highlight similarities and differences between MaMybA and MaAN2.

RESULTS

In this study, a novel anthocyanin-related R2R3-MYB gene was isolated from M. armeniacum flowers and functionally identified. A sequence alignment showed that MaMybA contained motifs typically conserved with MaAN2 and its orthologs. However, the shared identity of the entire amino acid sequence between MaMybA and MaAN2 was 43.5%. Phylogenetic analysis showed that they were both clustered into the AN2 subgroup of the R2R3-MYB family, but not in the same branch. We also identified a IIIf bHLH protein, MabHLH1, in M. armeniacum flowers. A bimolecular fluorescence complementation assay showed that MabHLH1 interacted with MaMybA or MaAN2 in vivo; a dual luciferase assay indicated that MaMybA alone or in interaction with MabHLH1 could regulate the expression of MaDFR and AtDFR, but MaAN2 required MabHLH1 to do so. When overexpressing MaMybA in Nicotiana tabacum 'NC89', the leaves, petals, anthers, and calyx of transgenic tobacco showed intense and magenta anthocyanin pigments, whereas those of OE-MaAN2 plants had lighter pigmentation. However, the ovary wall and seed skin of OE-MaMybA tobacco were barely pigmented, while those of OE-MaAN2 tobacco were reddish-purple. Moreover, overexpressing MaMybA in tobacco obviously improved anthocyanin pigmentation, compared to the OE-MaAN2 and control plants, by largely upregulating anthocyanin biosynthetic and endogenous bHLH genes. Notably, the increased transcription of NtF3'5'H in OE-MaMybA tobacco might lead to additional accumulation of delphinidin 3-rutinoside, which was barely detected in OE-MaAN2 and control plants. We concluded that the high concentration of anthocyanin and the newly produced Dp3R caused the darker color of OE-MaMybA compared to OE-MaAN2 tobacco.

CONCLUSION

The newly identified R2R3-MYB transcription factor MaMybA functions in anthocyanin biosynthesis, but has some differences from MaAN2; MaMybA could also be useful in modifying flower color in ornamental plants.

Ethylene Induces a Rapid Degradation of Petal Anthocyanins in Cut Vanda 'Sansai Blue' Orchid Flowers

Ethylene plays a major role in the regulation of flower senescence, including in the ethylene-sensitive Vanda 'Sansai Blue' orchid flowers. This cut flower is popular in Thailand due to its light blue big size florets possessing a beautiful shape pattern. In the present study, we further examined the rapid ethylene-induced process of active anthocyanin degradation in cut Vanda 'Sansai Blue' flowers, which occurred much before detection of other typical senescence-related symptoms. For this purpose, the cut inflorescences were exposed to air (control), 1 or 10 μl L-1 ethylene for 24 h, or to 0.2 μl L-1 1-methylcyclopropene (1-MCP) for 6 h followed by 10 μl L-1 ethylene for 24 h at 21°C, and the effects of these treatments on various parameters were assayed. While the fading-induced effect of ethylene was not concentration-dependent in this range, the ethylene treatment significantly reduced the flower vase life in a concentration-dependent manner, further confirming the separation of the bleaching process from senescence. Exposure of the inflorescences to 1-MCP pre-treatment followed by 10 μl L-1 ethylene, recovered both inflorescence color and anthocyanin content to control levels. Quantification of total anthocyanin content, performed by HPLC analysis on the basis of cyanidin-3-glocuside equivalents, showed that ethylene reduced and 1-MCP recovered the anthocyanins profile in non-hydrolyzed anthocyanin samples of Vanda 'Sansai Blue' florets, assayed at half bloom and bloom developmental stages. The results showed that the ethylene-induced color fading, observed immediately after treatment, resulted from a significant reduction in the levels of the two main anthocyanidins, cyanidin and delphinidin, as well as of other anthocyanidins present in low abundance, but not from changes in the levels of flavonols, such as kaempferol. This anthocyanin degradation process seems to operate via ethylene-increased peroxidase activity, detected at the bud stage. Taken together, our results suggest that the ethylene-induced rapid color bleaching in petals of cut Vanda 'Sansai Blue' flowers is an outcome of in-planta anthocyanin degradation, partially mediated by increased peroxidase activity, and proceeds independently of the flower senescence process.

Metabolic and molecular analysis of nonuniform anthocyanin pigmentation in tomato fruit under high light

Pigment intensity and patterns are important factors that determine the nutritional and market values of tomato fruits. The acropetal manner of light-dependent anthocyanin accumulation with the highest levels at the stem end of the fruit makes Pro35S:BrTT8 tomato plants an ideal system for investigating the effects of light intensity on anthocyanin biosynthesis. Extensive transcript analyses indicate that anthocyanin pigmentation in Pro35S:BrTT8 plants under high light might be coordinately regulated by the exogenous protein BrTT8 and endogenous proteins SlAN2 and SlMYBL2. Furthermore, yeast two-hybrid assays showed that BrTT8 could interact efficiently with SlAN2, SlMYBL2, and SlAN11. Moreover, the physical interaction between BrTT8 and SlAN2 was validated by FRET. Simultaneous overexpression of SlAN2 and BrTT8 activated significant anthocyanin biosynthesis in infiltrated tobacco leaves. In addition, the ability of SlMYBL2 to suppress anthocyanin accumulation was also demonstrated in infiltrated tobacco leaves. Altogether, these results prove that tissue-specific assemblage of the heterogeneous MYB-bHLH-WD40 complex consisting of SlAN2, BrTT8 and SlAN11 triggers nonuniform anthocyanin accumulation in tomato fruit under high light. Additionally, it is proposed that a negative-feedback loop fulfilled by SlMYBL2 also participates in the regulation of anthocyanin production.

RNA sequencing and anthocyanin synthesis-related genes expression analyses in white-fruited Vaccinium uliginosum

BACKGROUND

Vaccinium uliginosum (Ericaceae) is an important wild berry having high economic value. The white-fruited V. uliginosum variety found in the wild lacks anthocyanin and bears silvery white fruits. Hence, it is a good resource for investigating the mechanism of fruit color development. This study aimed to verify the differences in the expression levels of some structural genes and transcription factors affecting the anthocyanin biosynthesis pathway by conducting high-throughput transcriptome sequencing and real-time PCR analysis by using the ripening fruits of V. uliginosum and the white-fruited variety.

RESULTS

We annotated 42,837 unigenes. Of the 325 differentially expressed genes, 41 were up-regulated and 284 were down-regulated. Further, 11 structural genes of the flavonoid pathway were up-regulated, whereas two were down-regulated. Of the seven genes encoding transcription factors, five were up-regulated and two were down-regulated. The structural genes VuCHS, VuF3'H, VuFHT, VuDFR, VuANS, VuANR, and VuUFGT and the transcription factors VubHLH92, VuMYB6, VuMYBPA1, VuMYB11, and VuMYB12 were significantly down-regulated. However, the expression of only VuMYB6 and VuMYBPA1 rapidly increased during the last two stages of V. uliginosum when the fruit was ripening, consistent with anthocyanin accumulation.

CONCLUSIONS

VuMYB6 was annotated as MYB1 by the BLAST tool. Thus, the white fruit color in the V. uliginosum variant can be attributed to the down-regulation of transcription factors VuMYB1 and VuMYBPA1, which leads to the down-regulation of structural genes associated with the anthocyanin synthesis pathway.

Transcriptional activation of anthocyanin structural genes in Torenia 'Kauai Rose' via overexpression of anthocyanin regulatory transcription factors

This study was conducted to examine the role of the transcription factors (TFs), RsMYB1 and mPAP1 together with B-Peru (mPAP1 + B-Peru), in regulating anthocyanin biosynthesis in the ornamental torenia (Torenia fournieri) cultivar Kauai Rose using Agrobacterium-mediated transformation. Expression levels of RsMYB1 were the highest in the lines RS5 and RS3, followed by RS4, RS2, and RS1, while transcript levels of mPAP1 + B-Peru increased in the order of PB-6 > PB-5 > PB-7 > PB-8 > PB-2. Moreover, transcript levels of the anthocyanin structural genes in transgenic lines were significantly higher than those in wild-type (WT) plants. Anthocyanin structural gene expression was specifically altered by TF overexpression: the highest expression of anthocyanidin synthase (ANS) was observed in transgenic lines with RsMYB1, while expression of dihydroflavonol-4-reductase (DFR) was the highest in lines with mPAP1 + B-Peru. We expect that enhanced expression of these anthocyanin structural genes will improve anthocyanin content in the flowers of transgenic torenia. Moreover, these results indicate that RsMYB1 and mPAP1 + B-Peru can be exploited as anthocyanin regulatory TFs to enhance anthocyanin content in other horticultural plants.

Successful floral-dipping transformation of post-anthesis lisianthus (Eustoma grandiflorum) flowers

The adaptation of the Agrobacterium-mediated floral-dipping technique is limited, to date, to a small number of plants. In this paper, we present the efficient transformation of one of the leading plants in the cut flower industry, lisianthus (Eustoma grandiflorum). This method is approximately 18 months shorter than the known tissue culture-based transformation. The Excalibur Pink cultivar and two additional breeding lines, X-1042 and X-2541, were transformed using three different marker genes (benzyl alcohol acetyltransferase (BEAT) originating from Clarkia breweri, the feedback-insensitive bacterial gene AroG*, and the empty pART27 vector expressing a kanamycin-resistance cassette (nptII)). Genomic transformation was successful in all tested cases with transformation efficiency ranked from 0.2 to 2.9%, which is well in the range of results from Arabidopsis studies. Unlike Arabidopsis, in which floral-dipping transformation was efficient only at a pre-anthesis stage before ovary sealing, lisianthus flowers were transformed when dipping occurred 4 days pre-anthesis or 3-5 days post-anthesis with 1.5 and 3.7% efficiencies, respectively. Post-anthesis transformation occurred when the flower ovaries were sealed. Flower dipping of Excalibur Pink flowers with fluorescent Agrobacterium containing a GFP marker gene demonstrated Agrobacterium entrance into the sealed flower ovary through the open stigma and style tube. In this study, we demonstrated floral-dipping transformation of a commercial plant, lisianthus Excalibur Pink, occurring after sealing of the ovaries, probably via the stigma and wide open style tunnel.

Roles of R2R3-MYB transcription factors in transcriptional regulation of anthocyanin biosynthesis in horticultural plants

This review contains functional roles of MYB transcription factors in the transcriptional regulation of anthocyanin biosynthesis in horticultural plants. This review describes potential uses of MYB TFs as tools for metabolic engineering for anthocyanin production. Anthocyanins (ranging from red to blue) are controlled by specific branches of the anthocyanin biosynthetic pathway and are mostly visible in ornamentals, fruits, and vegetables. In the present review, we describe which R2R3-MYB transcription factors (TFs) control the transcriptional regulation of anthocyanin structural genes involved in the specific branches of the anthocyanin biosynthetic pathway in various horticultural plants (e.g., ornamentals, fruits, and vegetables). In addition, some MYBs responsible for anthocyanin accumulation in specific tissues are described. Moreover, we highlight the phylogenetic relationships of the MYBs that suppress or promote anthocyanin synthesis in horticultural crops. Enhancement of anthocyanin synthesis via metabolic genetic engineering of anthocyanin MYBs, which is described in the review, is indicative of the potential use of the mentioned anthocyanin-related MYBs as tools for anthocyanin production. Therefore, the MYBs would be suitable for metabolic genetic engineering for improvement of flower colors, fruit quality, and vegetable nutrients.

Overexpression of Rosea1 From Snapdragon Enhances Anthocyanin Accumulation and Abiotic Stress Tolerance in Transgenic Tobacco

The co-expression of Rosea1 (Ros1) and Delila (Del) regulates anthocyanin levels in snapdragon flowers, as well as in tomato, petunia, and tobacco. However, there is little information on how Ros1 expression alone controls anthocyanin regulation and whether it is involved in the mechanism that leads to abiotic stress tolerance. In the present study, tobacco (Nicotiana tabacum 'Xanthi') transgenic plants overexpressing Ros1 (T2-Ros1-1, T2-Ros1-2, T2-Ros1-3, and T2-Ros1-4) promoted accumulation of anthocyanin in leaves and flowers by elevating the transcription of all key genes involved in the biosynthesis of this pigment. This promotion largely occurred through the upregulation of dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase genes in leaves and upregulation of DFR in flowers. Under normal conditions, the transgenic lines and wild type (WT) plants showed well-developed broad leaves and regular roots, whereas a reduction in plant growth was observed under cold and drought stresses. However, the transgenic T2-Ros1 lines were able to tolerate the stresses better than the WT line by inducing reactive oxygen species scavenging activities, and the expression of antioxidant-related and stress-responsive genes. In addition, phylogenetic analysis clustered Ros1 with many transcription factors (TFs) that confer tolerance to different abiotic stresses. Overall, the results obtained here suggest that Ros1 overexpression upregulates anthocyanin biosynthetic, antioxidant-related, and stress-responsive genes thereby enhancing anthocyanin accumulation and abiotic stress tolerance.

Quantitative Phosphoproteomic and Metabolomic Analyses Reveal GmMYB173 Optimizes Flavonoid Metabolism in Soybean under Salt Stress

Salinity causes osmotic stress to crops and limits their productivity. To understand the mechanism underlying soybean salt tolerance, proteomics approach was used to identify phosphoproteins altered by NaCl treatment. Results revealed that 412 of the 4698 quantitatively analyzed phosphopeptides were significantly up-regulated on salt treatment, including a phosphopeptide covering the serine 59 in the transcription factor GmMYB173. Our data showed that GmMYB173 is one of the three MYB proteins differentially phosphorylated on salt treatment, and a substrate of the casein kinase-II. MYB recognition sites exist in the promoter of flavonoid synthase gene GmCHS5 and one was found to mediate its recognition by GmMYB173, an event facilitated by phosphorylation. Because GmCHS5 catalyzes the synthesis of chalcone, flavonoids derived from chalcone were monitored using metabolomics approach. Results revealed that 24 flavonoids of 6745 metabolites were significantly up-regulated after salt treatment. We further compared the salt tolerance and flavonoid accumulation in soybean transgenic roots expressing the 35S promoter driven cds and RNAi constructs of GmMYB173 and GmCHS5, as well as phospho-mimic (GmMYB173S59D ) and phospho-ablative (GmMYB173S59A ) mutants of GmMYB173 Overexpression of GmMYB173S59D and GmCHS5 resulted in the highest increase in salt tolerance and accumulation of cyaniding-3-arabinoside chloride, a dihydroxy B-ring flavonoid. The dihydroxy B-ring flavonoids are more effective as anti-oxidative agents when compared with monohydroxy B-ring flavonoids, such as formononetin. Hence the salt-triggered phosphorylation of GmMYB173, subsequent increase in its affinity to GmCHS5 promoter and the elevated transcription of GmCHS5 likely contribute to soybean salt tolerance by enhancing the accumulation of dihydroxy B-ring flavonoids.

Transcriptome profiling of genes related to light-induced anthocyanin biosynthesis in eggplant (Solanum melongena L.) before purple color becomes evident

Background

The anthocyanins are highly enriched in eggplants (Solanum melongena L.) with purple peel. However, our previous study showed that anthocyanins biosynthesis in eggplant cultivar ‘Lanshan Hexian’ was completely regulated by light and color becomes evident at most 2 days after exposure to light. In the present investigation, transcriptome study was made to explore the underlying molecular mechanisms of light-induced anthocyanin biosynthesis in eggplant (Solanum melongena L.) before color becomes evident.

Results

RNA-Seq was performed for four time points (0, 0.5, 4 and 8 h after bags removal) where concerted changes happened. A total of 32,630 genes or transcripts were obtained by transcriptome sequencing, from which 1956 differentially expressed genes (DEGs) were found. Gene Ontology analysis showed that the 1956 DEGs covered a wide range of cellular components, molecular functions and biological processes. All the DEGs were further divided into 26 clusters based on their distinct expression patterns. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis found out 24 structural anthocyanin biosynthesis genes which distributing in seven clusters. In addition, 102 transcription factors, which exhibited highly dynamic changes in response to light, were found in the seven clusters. Three photoreceptors, UV Resistance Locus 8 (UVR8), Cryptochrome 3 (CRY3) and UVR3, were identified as DEGs. The light signal transduction elements, COP1 and two SPAs, might be responsible for anthocyanin biosynthesis regulation.

Conclusion

Based on the transcriptome data, the anthocyanin biosynthesis structural genes, transcription factors, photoreceptors and light signal transduction elements were quickly screened which may act as the key regulatory factors in anthocyanin biosynthesis pathway. By comparing the transcriptome data with our previous studies, 869 genes were confirmed to participate in the light-induced anthocyanin biosynthesis. These results expand our knowledge of light-induced anthocyanin biosynthesis in plants, which allowing for fruit coloration to be improved under low-light conditions in future.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4587-z) contains supplementary material, which is available to authorized users.

Enhancing Flower Color through Simultaneous Expression of the B-peru and mPAP1 Transcription Factors under Control of a Flower-Specific Promoter

Flower color is a main target for flower breeding. A transgenic approach for flower color modification requires a transgene and a flower-specific promoter. Here, we expressed the B-peru gene encoding a basic helix loop helix (bHLH) transcription factor (TF) together with the mPAP1 gene encoding an R2R3 MYB TF to enhance flower color in tobacco (Nicotiana tabacum L.), using the tobacco anthocyanidin synthase (ANS) promoter (PANS) to drive flower-specific expression. The transgenic tobacco plants grew normally and produced either dark pink (PANSBP_DP) or dark red (PANSBP_DR) flowers. Quantitative real time polymerase chain reaction (qPCR) revealed that the expression of five structural genes in the flavonoid biosynthetic pathway increased significantly in both PANSBP_DP and PANSBP_DR lines, compared with the non-transformed (NT) control. Interestingly, the expression of two regulatory genes constituting the active MYB-bHLH-WD40 repeat (WDR) (MBW) complex decreased significantly in the PANSBP_DR plants but not in the PANSBP_DP plants. Total flavonol and anthocyanin abundance correlated with flower color, with an increase of 1.6-43.2 fold in the PANSBP_DP plants and 2.0-124.2 fold in the PANSBP_DR plants. Our results indicate that combinatorial expression of B-peru and mPAP1 genes under control of the ANS promoter can be a useful strategy for intensifying flower color without growth retardation.

AgFNS overexpression increase apigenin and decrease anthocyanins in petioles of transgenic celery

Apigenin and anthocyanin biosyntheses share common precursors in plants. Flavone synthase (FNS) converts naringenin into apigenin in higher plants. Celery is an important edible and medical vegetable crop that contains apigenin in its tissues. However, the effect of high AgFNS gene expression on the apigenin and anthocyanins contents of purple celery remains to be elucidated. In this study, the AgFNS gene was cloned from purple celery ('Nanxuan liuhe purple celery') and overexpressed in this purple celery to determine its influence on anthocyanins and apigenin contents. Results showed that the AgFNS gene was 1068bp, which encodes 355 amino acid residues. Evolution analysis showed that the AgFNS protein belongs to the FSN I type. In AgFNS transgenic celery, the anthocyanins content in petioles was lower than that wild-type celery plants. Apigenin content increased in the petioles of AgFNS transgenic celery. The transcript levels of the AgPAL, AgC4H, AgCHS, and AgCHI genes were up-regulated, whereas those of the AgF3H, AgF3'H, AgDFR, AgANS, and Ag3GT genes were down-regulated in the petioles of AgFNS transgenic plants compared with wild-type celery plants. This work provides basic knowledge about the function of the AgFNS gene in the anthocyanin and apigenin biosyntheses of celery.

High accumulation of anthocyanins via the ectopic expression of AtDFR confers significant salt stress tolerance in Brassica napus L

The ectopic expression of AtDFR results in increased accumulation of anthocyanins leading to enhanced salinity and drought stress tolerance in B. napus plants. Flavonoids with antioxidant effects confer many additional benefits to plants. Evidence indicates that flavonoids, including anthocyanins, protect tissues against oxidative stress from various abiotic stressors. We determined whether increases in anthocyanins increased abiotic stress tolerance in Brassica napus, because the values of B. napus L. and its cultivation area are increasing worldwide. We overexpressed Arabidopsis dihydroflavonol-4-reductase (DFR) in B. napus. Increased DFR transcript levels for AtDFR-OX B. shoots correlated with higher anthocyanin accumulation. AtDFR-OX Brassica shoots exhibited lower reactive oxygen species (ROS) accumulation than wild-type (WT) shoots under high NaCl and mannitol concentrations. This was corroborated by 3,3-diaminobenzidine staining for ROS scavenging activity in 1,1-diphenyl-2-picryl-hydrazyl assays. Shoots of the AtDFR-OX B. napus lines grown in a high salt medium exhibited enhanced salt tolerance and higher chlorophyll content than similarly grown WT plants. Our observations suggested that the AtDFR gene can be effectively manipulated to modulate salinity and drought stress tolerance by directing to high accumulation of anthocyanins in oilseed plants.

Biotechnological Advancements for Improving Floral Attributes in Ornamental Plants

Developing new ornamental cultivars with improved floral attributes is a major goal in floriculture. Biotechnological approach together with classical breeding methods has been used to modify floral color, appearance as well as for increasing disease resistance. Transgenic strategies possess immense potential to produce novel flower phenotypes that are not found in nature. Adoption of Genetic engineering has supported the idea of floral trait modification. Ornamental plant attributes like floral color, fragrance, disease resistance, and vase life can be improved by means of genetic manipulation. Therefore, we witness transgenic plant varieties of high aesthetic and commercial value. This review focuses on biotechnological advancements in manipulating key floral traits that contribute in development of diverse ornamental plant lines. Data clearly reveals that regulation of biosynthetic pathways related to characteristics like pigment production, flower morphology and fragrance is both possible and predictable. In spite of their great significance, small number of genetically engineered varieties of ornamental plants has been field tested. Today, novel flower colors production is regarded as chief commercial benefit obtained from transgenic plants. But certain other floral traits are much more important and have high commercial potential. Other than achievements such as novel architecture, modified flower color, etc., very few reports are available regarding successful transformation of other valuable horticultural characteristics. Our review also summarized biotechnological efforts related to enhancement of fragrance and induction of early flowering along with changes in floral anatomy and morphology.

Identification of Norway Spruce MYB-bHLH-WDR Transcription Factor Complex Members Linked to Regulation of the Flavonoid Pathway

Transcription factors (TFs) forming MYB-bHLH-WDR complexes are known to regulate the biosynthesis of specialized metabolites in angiosperms through an intricate network. These specialized metabolites participate in a wide range of biological processes including plant growth, development, reproduction as well as in plant immunity. Studying the regulation of their biosynthesis is thus essential. While MYB (TFs) have been previously shown to control specialized metabolism (SM) in gymnosperms, the identity of their partners, in particular bHLH or WDR members, has not yet been revealed. To gain knowledge about MYB-bHLH-WDR transcription factor complexes in gymnosperms and their regulation of SW, we identified two bHLH homologs of AtTT8, six homologs of the MYB transcription factor AtTT2 and one WDR ortholog of AtTTG1 in Norway spruce. We investigated the expression levels of these genes in diverse tissues and upon treatments with various stimuli including methyl-salicylate, methyl-jasmonate, wounding or fungal inoculation. In addition, we also identified protein-protein interactions among different homologs of MYB, bHLH and WDR. Finally, we generated transgenic spruce cell lines overexpressing four of the Norway spruce AtTT2 homologs and observed differential regulation of genes in the flavonoid pathway and flavonoid contents.

Overexpression of AmRosea1 Gene Confers Drought and Salt Tolerance in Rice

Ectopic expression of the MYB transcription factor of AmROSEA1 from Antirrhinum majus has been reported to change anthocyanin and other metabolites in several species. In this study, we found that overexpression of AmRosea1 significantly improved the tolerance of transgenic rice to drought and salinity stresses. Transcriptome analysis revealed that a considerable number of stress-related genes were affected by exogenous AmRosea1 during both drought and salinity stress treatments. These affected genes are involved in stress signal transduction, the hormone signal pathway, ion homeostasis and the enzymes that remove peroxides. This work suggests that the AmRosea1 gene is a potential candidate for genetic engineering of crops.

Sucrose-induced anthocyanin accumulation in vegetative tissue of Petunia plants requires anthocyanin regulatory transcription factors

The effects of three different sucrose concentrations on plant growth and anthocyanin accumulation were examined in non-transgenic (NT) and transgenic (T₂) specimens of the Petunia hybrida cultivar 'Mirage rose' that carried the anthocyanin regulatory transcription factors B-Peru+mPAP1 or RsMYB1. Anthocyanin accumulation was not observed in NT plants in any treatments, whereas a range of anthocyanin accumulation was observed in transgenic plants. The anthocyanin content detected in transgenic plants expressing the anthocyanin regulatory transcription factors (B-Peru+mPAP1 or RsMYB1) was higher than that in NT plants. In addition, increasing sucrose concentration strongly enhanced anthocyanin content as shown by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, wherein increased concentrations of sucrose enhanced transcript levels of the transcription factors that are responsible for the induction of biosynthetic genes involved in anthocyanin synthesis; this pattern was not observed in NT plants. In addition, sucrose affected plant growth, although the effects were different between NT and transgenic plants. Taken together, the application of sucrose could enhance anthocyanin production in vegetative tissue of transgenic Petunia carrying anthocyanin regulatory transcription factors, and this study provides insights about interactive effects of sucrose and transcription factors in anthocyanin biosynthesis in the transgenic plant.

Floral traits and pollination ecology of European Arum hybrids

Hybridisation is common in plants and can affect the genetic diversity and ecology of sympatric parental populations. Hybrids may resemble the parental species in their ecology, leading to competition and/or gene introgression; alternatively, they may diverge from the parental phenotypes, possibly leading to the colonisation of new ecological niches and to speciation. Here, we describe inflorescence morphology, ploidy levels, pollinator attractive scents, and pollinator guilds of natural hybrids of Arum italicum and A. maculatum (Araceae) from a site with sympatric parental populations in southern France to determine how these traits affect the hybrid pollination ecology. Hybrids were characterised by inflorescences with a size and a number of flowers more similar to A. italicum than to A. maculatum. In most cases, hybrid stamens were purple, as in A. maculatum, and spadix appendices yellow, as in A. italicum. Hybrid floral scent was closer to that of A. italicum, but shared some compounds with A. maculatum and comprised unique compounds. Also, the pollinator guild of the hybrids was similar to that of A. italicum. Nevertheless, the hybrids attracted a high proportion of individuals of the main pollinator of A. maculatum. We discuss the effects of hybridisation in sympatric parental zones in which hybrids exhibit low levels of reproductive success, the establishment of reproductive barriers between parental species, the role of the composition of floral attractive scents in the differential attraction of pollinators and in the competition between hybrids and their parental species, and the potential of hybridisation to give rise to new independent lineages.

Anthocyanin accumulation enhanced in Lc-transgenic cotton under light and increased resistance to bollworm

Breeding of naturally colored cotton fiber has been hampered by the limited germplasm, an alternative way is to use transgenic approach to create more germplasm for breeding. Here, we report our effort to engineer anthocyanin production in cotton. The maize Lc gene, under the control of the constitutive 35S promoter, was introduced into cotton through genetic transformation. Our data showed that the expression of the Lc gene alone is sufficient to trigger the accumulation of anthocyanin in a variety of cell types including fiber cells in cotton. However, the accumulation of colored anthocyanin in cotton fibers requires the participation of light signaling. These data indicate that it is feasible to engineer colored fibers through transgenic approach in cotton. Furthermore, we showed that the Lc-transgenic cotton plants are resistant to cotton bollworm. These transgenic plants are, therefore, potentially useful for cotton breeding against cotton bollworm.

The Arabidopsis Transcription Factor MYB112 Promotes Anthocyanin Formation during Salinity and under High Light Stress

MYB transcription factors (TFs) are important regulators of flavonoid biosynthesis in plants. Here, we report MYB112 as a formerly unknown regulator of anthocyanin accumulation in Arabidopsis (Arabidopsis thaliana). Expression profiling after chemically induced overexpression of MYB112 identified 28 up- and 28 down-regulated genes 5 h after inducer treatment, including MYB7 and MYB32, which are both induced. In addition, upon extended induction, MYB112 also positively affects the expression of PRODUCTION OF ANTHOCYANIN PIGMENT1, a key TF of anthocyanin biosynthesis, but acts negatively toward MYB12 and MYB111, which both control flavonol biosynthesis. MYB112 binds to an 8-bp DNA fragment containing the core sequence (A/T/G)(A/C)CC(A/T)(A/G/T)(A/C)(T/C). By electrophoretic mobility shift assay and chromatin immunoprecipitation coupled to quantitative polymerase chain reaction, we show that MYB112 binds in vitro and in vivo to MYB7 and MYB32 promoters, revealing them as direct downstream target genes. We further show that MYB112 expression is up-regulated by salinity and high light stress, environmental parameters that both require the MYB112 TF for anthocyanin accumulation under these stresses. In contrast to several other MYB TFs affecting anthocyanin biosynthesis, MYB112 expression is not controlled by nitrogen limitation or an excess of carbon. Thus, MYB112 constitutes a regulator that promotes anthocyanin accumulation under abiotic stress conditions.

Failure to launch: the self-regulating Md-MYB10 R6 gene from apple is active in flowers but not leaves of Petunia

The Md - MYB10 R6 gene from apple is capable of self-regulating in heterologous host species and enhancing anthocyanin pigmentation, but the activity of MYB10 is dependent on endogenous protein partners. Coloured foliage due to anthocyanin pigments (bronze/red/black) is an attractive trait that is often lacking in many bedding, ornamental and horticultural plants. Apples (Malus × domestica) containing an allelic variant of the anthocyanin regulator, Md-MYB10 R6 , are highly pigmented throughout the plant, due to autoregulation by MYB10 upon its own promoter. We investigated whether Md-MYB10 R6 from apple is capable of functioning within the heterologous host Petunia hybrida to generate plants with novel pigmentation patterns. The Md-MYB10 R6 transgene (MYB10-R6 pro :MYB10:MYB10 term ) activated anthocyanin synthesis when transiently expressed in Antirrhinum rosea (dorsea) petals and petunia leaf discs. Stable transgenic petunias containing Md-MYB10 R6 lacked foliar pigmentation but had coloured flowers, complementing the an2 phenotype of 'Mitchell' petunia. The absence of foliar pigmentation was due to the failure of the Md-MYB10 R6 gene to self-activate in vegetative tissues, suggesting that additional protein partners are required for Md-MYB10 to activate target genes in this heterologous system. In petunia flowers, where endogenous components including MYB-bHLH-WDR (MBW) proteins were present, expression of the Md-MYB10 R6 promoter was initiated, allowing auto-regulation to occur and activating anthocyanin production. Md-MYB10 is capable of operating within the petunia MBW gene regulation network that controls the expression of the anthocyanin biosynthesis genes, AN1 (bHLH) and MYBx (R3-MYB repressor) in petals.

Promotion of flavonoid biosynthesis in leaves and calli of ornamental crabapple (Malus sp.) by high carbon to nitrogen ratios

Flavonoids are secondary metabolites that play important roles in plant physiology. Despite numerous studies examined the effects of available carbon (C) or nitrogen (N) on flavonoid biosynthesis, the mechanism of C/N interactive effects on flavonoid metabolism is still unclear. In this study, we analyzed the composition of flavonoids and the expression levels of flavonoid-related genes in leaves and calli of crabapple (Malus sp.) cultivars with different leaf colors grown on media with different C/N ratios. Our results show that high C/N ratios induce anthocyanin pigmentation in leaves of the ever-red cultivar 'Royalty' and the spring-red cultivar 'Prairifire,' as well as in three types of calli derived from the ever-green cultivar 'Spring Snow,' but not in the leaves of the ever-green cultivar 'Flame.' This phenomenon therefore correlated with anthocyanin content in these different samples. In addition, high C/N ratios in the growth media resulted in an increase in the concentration of flavones and flavonols in the leaves of the three crabapple cultivars. The transcript levels of the general flavonoid pathway genes [from chalcone synthase (CHS) to uridine diphosphat-glucose: flavonoid 3-O-glycosyltransferase (UFGT) and flavonol synthase (FLS)] increased in response to high C/N ratios, and this in turn was correlated with the concentration of anthocyanins, flavones and flavonols in the leaves and calli. Expression of the late flavonoid/anthocyanin biosynthetic genes, anthocyanidin synthase (ANS), UFGT and FLS in particular, was more strongly influenced by C/N ratios than other structural genes, and the increased expression of the structural genes under high C/N ratios coincided with a coordinated increase in transcript levels of a MYB transcription factor, MYB10. These results are likely to be useful for future generation of plants with an optimized flavonoid/anthocyanin content or desirable organ coloration.

Comparing Gene Expression Profiles Between Bt and non-Bt Rice in Response to Brown Planthopper Infestation

Bt proteins are the most widely used insecticidal proteins in transgenic crops for improving insect resistance. We previously observed longer nymphal developmental duration and lower fecundity in brown planthopper (BPH) fed on Bt rice line KMD2, although Bt insecticidal protein Cry1Ab could rarely concentrate in this non-target rice pest. In the present study, we performed microarray analysis in an effort to detect Bt-independent variation, which might render Bt rice more defensive and/or less nutritious to BPH. We detected 3834 and 3273 differentially expressed probe-sets in response to BPH infestation in non-Bt parent Xiushui 11 and Bt rice KMD2, respectively, only 439 of which showed significant differences in expression between rice lines. Our analysis revealed a shift from growth to defense responses in response to BPH infestation, which was also detected in many other studies of plants suffering biotic and abiotic stresses. Chlorophyll biosynthesis and basic metabolism pathways were inhibited in response to infestation. IAA and GA levels decreased as a result of the repression of biosynthesis-related genes or the induction of inactivation-related genes. In accordance with these observations, a number of IAA-, GA-, BR-signaling genes were downregulated in response to BPH. Thus, the growth of rice plants under BPH attack was reduced and defense related hormone signaling like JA, SA and ET were activated. In addition, growth-related hormone signaling pathways, such as GA, BR, and auxin signaling pathways, as well as ABA, were also found to be involved in BPH-induced defense. On the other side, 51 probe-sets (represented 50 genes) that most likely contribute to the impact of Bt rice on BPH were identified, including three early nodulin genes, four lipid metabolic genes, 14 stress response genes, three TF genes and genes with other functions. Two transcription factor genes, bHLH and MYB, together with lipid transfer protein genes LTPL65 and early nodulin gene ENOD93, are the most likely candidates for improving herbivore resistance in plants.