Engineered native pathways for high kaempferol and caffeoylquinate production in potato

Unveiling phenylpropanoid regulation: the role of DzMYB activator and repressor in durian (Durio zibethinus) fruit

KEY MESSAGE

DzMYB2 functions as an MYB activator, while DzMYB3 acts as an MYB repressor. They bind to promoters, interact with DzbHLH1, and influence phenolic contents, revealing their roles in phenylpropanoid regulation in durian pulps. Durian fruit has a high nutritional value attributed to its enriched bioactive compounds, including phenolics, carotenoids, and vitamins. While various transcription factors (TFs) regulate phenylpropanoid biosynthesis, MYB (v-myb avian myeloblastosis viral oncogene homolog) TFs have emerged as pivotal players in regulating key genes within this pathway. This study aimed to identify additional candidate MYB TFs from the transcriptome database of the Monthong cultivar at five developmental/postharvest ripening stages. Candidate transcriptional activators were discerned among MYBs upregulated during the ripe stage based on the positive correlation observed between flavonoid biosynthetic genes and flavonoid contents in ripe durian pulps. Conversely, MYBs downregulated during the ripe stage were considered candidate repressors. This study focused on a candidate MYB activator (DzMYB2) and a candidate MYB repressor (DzMYB3) for functional characterization. LC-MS/MS analysis using Nicotiana benthamiana leaves transiently expressing DzMYB2 revealed increased phenolic compound contents compared with those in leaves expressing green fluorescence protein controls, while those transiently expressing DzMYB3 showed decreased phenolic compound contents. Furthermore, it was demonstrated that DzMYB2 controls phenylpropanoid biosynthesis in durian by regulating the promoters of various biosynthetic genes, including phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR). Meanwhile, DzMYB3 regulates the promoters of PAL, 4-coumaroyl-CoA ligase (4CL), CHS, and CHI, resulting in the activation and repression of gene expression. Moreover, it was discovered that DzMYB2 and DzMYB3 could bind to another TF, DzbHLH1, in the regulation of flavonoid biosynthesis. These findings enhance our understanding of the pivotal role of MYB proteins in regulating the phenylpropanoid pathway in durian pulps.

Chemically Mediated Plant-Plant Interactions: Allelopathy and Allelobiosis

Plant-plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant-plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant-plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant-plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant-plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root-soil interactions and plant-soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant-plant interactions.

Integrated transcriptomic and metabolomic analysis revealed altitude-related regulatory mechanisms on flavonoid accumulation in potato tubers

Not least because it is adaptable to a variety of geographies and climates, potato (Solanum tuberosum L.) is grown across much of the world. Pigmented potato tubers have been found to contain large quantities of flavonoids, which have various functional roles and act as antioxidants in the human diet. However, the effect of altitude on the biosynthesis and accumulation of flavonoids in potato tubers is poorly characterized. Here we carried out an integrated metabolomic and transcriptomic study in order to evaluate how cultivation at low (800 m), moderate (1800 m), and high (3600 m) altitude affects flavonoid biosynthesis in pigmented potato tubers. Both red and purple potato tubers grown at a high altitude contained the highest flavonoid content, and the most highly pigmented flesh, followed by those grown at a low altitude. Co-expression network analysis revealed three modules containing genes which were positively correlated with altitude-responsive flavonoid accumulation. The anthocyanin repressors StMYBATV and StMYB3 exhibited a significant positive relationship with altitude-responsive flavonoid accumulation. The repressive function of StMYB3 was further verified in tobacco flowers and potato tubers. The results presented here add to the growing body of knowledge regarding the response of flavonoid biosynthesis to environmental conditions, and should aid in efforts to develop novel varieties of pigmented potatoes for use across different geographies.

Safflower Flavonoid 3′5′Hydroxylase Promotes Methyl Jasmonate-induced Anthocyanin Accumulation in Transgenic Plants

Flavonoids are the most abundant class of secondary metabolites that are ubiquitously involved in plant development and resistance to biotic and abiotic stresses. Flavonoid biosynthesis involves multiple channels of orchestrated molecular regulatory factors. Methyl jasmonate (MeJA) has been demonstrated to enhance flavonoid accumulation in numerous plant species; however, the underlying molecular mechanism of MeJA-induced flavonoid biosynthesis in safflower is still not evident. In the present study, we revealed the underlying molecular basis of a putative F3′5′H gene from safflower imparting MeJA-induced flavonoid accumulation in transgenic plants. The constitutive expression of the CtF3′5′H1 gene was validated at different flowering stages, indicating their diverse transcriptional regulation through flower development in safflower. Similarly, the CtF3′5′H1-overexpressed Arabidopsis plants exhibit a higher expression level, with significantly increased anthocyanins and flavonoid content, but less proanthocyanidins than wild-type plants. In addition, transgenic plants treated with exogenous MeJA revealed the up-regulation of CtF3′5′H1 expression over different time points with significantly enhanced anthocyanin and flavonoid content as confirmed by HPLC analysis. Moreover, CtF3′5′H1- overexpressed Arabidopsis plants under methyl violet and UV-B irradiation also indicated significant increase in the expression level of CtF3′5′H1 with improved anthocyanin and flavonoid content, respectively. Noticeably, the virus-induced gene silencing (VIGS) assay of CtF3′5′H1 in safflower leaves also confirmed reduced anthocyanin accumulation. However, the CtF3′5′H1 suppression in safflower leaves under MeJA elicitation demonstrated significant increase in total flavonoid content. Together, our findings confirmed that CtF3′5′H1 is likely mediating methyl jasmonate-induced flavonoid biosynthesis in transgenic plants via enhanced anthocyanin accumulation.

Cross-Talk and Physiological Role of Jasmonic Acid, Ethylene, and Reactive Oxygen Species in Wound-Induced Phenolic Biosynthesis in Broccoli

Wounding induces phenolic biosynthesis in broccoli. However, there is scarce information about the physiological and molecular mechanisms governing this stress response. In the present study, a chemical-genetics approach was used to elucidate the role of reactive oxygen species (ROS), jasmonic acid (JA), and ethylene (ET) as stress-signaling molecules in the wound-induced phenolic biosynthesis in broccoli. Wounding activated the biosynthesis of ET and JA. Likewise, the wound-induced biosynthesis of ET and JA was regulated by ROS. JA activated primary metabolism, whereas the three signaling molecules activated phenylpropanoid metabolism. The signaling molecules inhibited the wound-induced activation of the hydroxycinnamoyl-CoA quinate hydroxycinnamoyl transferase (HQT) gene, which is involved in caffeoylquinic acids biosynthesis, and the main phenolics accumulated in wounded broccoli, suggesting that an alternative caffeoylquinic biosynthesis pathway is activated in the tissue due to wounding. ROS mediated the biosynthesis of most individual phenolic compounds evaluated. In conclusion, ROS, ET, and JA are essential in activating broccoli's primary and secondary metabolism, resulting in phenolic accumulation.

Integrative analysis of metabolome and transcriptome reveals a dynamic regulatory network of potato tuber pigmentation

Potatoes consist of flavonoids that provide health benefits for human consumers. To learn more about how potato tuber flavonoid accumulation and flesh pigmentation are controlled, we analyzed the transcriptomic and metabolomic profile of potato tubers from three colored potato clones at three developmental phases using an integrated approach. From the 72 flavonoids identified in pigmented flesh, differential abundance was noted for anthocyanins, flavonols, and flavones. Weighted gene co-expression network analysis further allowed modules and candidate genes that positively or negatively regulate flavonoid biosynthesis to be identified. Furthermore, an R2R3-MYB repressor StMYB3 and an R3-MYB repressor StMYBATV involved in the modulation of anthocyanin biosynthesis during tuber development were identified. Both StMYB3 and StMYBATV could interact with the cofactor StbHLH1 and repress anthocyanin biosynthesis. Our results indicate a feedback regulatory mechanism of a coordinated MYB activator-repressor network on fine-tuning of potato tuber pigmentation during tuber development.

Metabolomic Characterization of Pigmented and Non-Pigmented Potato Cultivars Using a Joint and Individual Variation Explained (JIVE)

Potatoes (Solanum tuberosum L.) are one of the most valuable agricultural crops, and the flesh of these tubers provides various classes of healthy compounds important for human nutrition. This work presents the results of a joint analysis of different chemical classes of compounds which provided insights on the metabolic characterization of pigmented and non-pigmented potato varieties collected from Italy. The identification of common or individual metabolic characteristics across the omic datasets (antioxidants, total polyphenolic content, polyphenols, and sugars) is conducted by Joint and Individual Variation Explained (JIVE), a data fusion multivariate approach. The common part of the multivariate model allowed the separation between non-pigmented and pigmented samples. Polyphenolic compounds were mainly responsible for the separation between purple-fleshed and red-skinned potatoes. An additional detailed analysis of the anthocyanin composition, including the acylated anthocyanins, allowed to pinpoint the diversities between the pigmented potato groups. Furthermore, the presence of an appreciable amount of hydroxycinnamic acids and anthocyanins in the purple-fleshed varieties, which are also characterized by a lower content of sugars, is found. Our results provide scientific evidence for the promotion of promising potato cultivars, which are characterized by a remarkable amount of various health benefit compounds.

Biochemical Characterization and Effects of Cooking Methods on Main Phytochemicals of Red and Purple Potato Tubers, a Natural Functional Food

Potato is a staple food crop and an important source of dietary energy. Its tubers contain several essential amino acids, vitamins, minerals and phytochemicals that contribute to the nutritional value of this important product. Recently, scientific interest has focused on purple and red potatoes that, due to the presence of anthocyanins, may be considered as natural powerful functional food. The aim of this study was to evaluate the characteristics of pigmented varieties, the types of anthocyanins accumulated and the level of both beneficial phytochemicals (vitamin C and chlorogenic acids, CGAs) and anti-nutritional compounds (glycoalkaloids) following various cooking methods. The analyses described the presence of a mix of several acylated anthocyanins in pigmented tubers along with high level of CGA. The amount of antioxidants was differently affected by heat treatments according to the type of molecule and the cooking methods used. In some cases, the beneficial compounds were made more available by heat treatments for the analytical detection as compared to raw materials. Data reported here describe both the agronomic properties of these pigmented varieties and the effects of food processing methods on bioactive molecules contained in this natural functional food. They may provide useful information for breeders aiming to develop new varieties that could include desirable agronomical and industrial processing traits.

Hydroxylation decoration patterns of flavonoids in horticultural crops: chemistry, bioactivity and biosynthesis

Flavonoids are the most widespread polyphenolic compounds and are important dietary constituents present in horticultural crops such as fruits, vegetables, and tea. Natural flavonoids are responsible for important quality traits, such as food colors and beneficial dietary antioxidants and numerous investigations have shown that intake of flavonoids can reduce the incidence of various non-communicable diseases (NCDs). Analysis of the thousands of flavonoids reported so far has shown that different hydroxylation modifications affect their chemical properties and nutritional values. These diverse flavonoids can be classified based on different hydroxylation patterns in the B, C, A rings and multiple structure-activity analyses have shown that hydroxylation decoration at specific positions markedly enhances their bioactivities. This review focuses on current knowledge concerning hydroxylation of flavonoids catalyzed by several different types of hydroxylase enzymes. Flavonoid 3'-hydroxylase (F3'H) and flavonoid 3'5'-hydroxylase (F3'5'H) are important enzymes for the hydroxylation of the B ring of flavonoids. Flavanone 3-hydroxylase (F3H) is key for the hydroxylation of the C ring, while flavone 6-hydroxylase (F6H) and flavone 8-hydroxylase (F8H) are key enzymes for hydroxylation of the A ring. These key hydroxylases in the flavonoid biosynthesis pathway are promising targets for the future bioengineering of plants and mass production of flavonoids with designated hydroxylation patterns of high nutritional importance. In addition, hydroxylation in key places on the ring may help render flavonoids ready for degradation, the catabolic turnover of which may open the door for new lines of inquiry.

Diversity: current and prospective secondary metabolites for nutrition and medicine

Plants have been used as sources of food, feed and medicine for millennia. The ever-increasing population has, however, dramatically increased the burden on our arable land to meet nutritional demand. Concomitantly, and in part due to poor nutrition, we are faced with massive increases in chronic diseases, meaning the need for medicine has also increased. Here, we look back on research in these areas, surveying the polyphenols as a case study for health-conferring metabolites. We conclude that the tools that will allow us to breed more nutritious crops are all at hand. We stress that collaboration between plant and medical research needs to be intensified in order to improve our understanding of the bioactivities. In doing so, we attempt to draw a roadmap for the use of plants for mid-21st Century human health.

Recent Advanced Metabolic and Genetic Engineering of Phenylpropanoid Biosynthetic Pathways

The MYB transcription factors (TFs) are evolving as critical role in the regulation of the phenylpropanoid and tanshinones biosynthetic pathway. MYB TFs relate to a very important gene family, which are involved in the regulation of primary and secondary metabolisms, terpenoids, bioactive compounds, plant defense against various stresses and cell morphology. R2R3 MYB TFs contained a conserved N-terminal domain, but the domain at C-terminal sorts them different regarding their structures and functions. MYB TFs suppressors generally possess particular repressive motifs, such as pdLNLD/ELxiG/S and TLLLFR, which contribute to their suppression role through a diversity of complex regulatory mechanisms. A novel flower specific "NF/YWSV/MEDF/LW" conserved motif has a great potential to understand the mechanisms of flower development. In the current review, we summarize recent advanced progress of MYB TFs on transcription regulation, posttranscriptional, microRNA, conserved motif and propose directions to future prospective research. We further suggest there should be more focus on the investigation for the role of MYB TFs in microalgae, which has great potential for heterologous protein expression system for future perspectives.

A R2R3-MYB transcriptional activator LmMYB15 regulates chlorogenic acid biosynthesis and phenylpropanoid metabolism in Lonicera macranthoides

Lonicera macranthoides Hand-Mazz is an important medicinal plant widely distributed in southern China that has long been used in Chinese traditional medicines. Chlorogenic acid (CGA, 3-caffeoylquinic acid) is the major biologically active ingredient in L. macranthoides. Although key CGA biosynthetic genes have been well documented, their transcriptional regulation remains largely unknown. In this study, we observed that a R2R3 MYB transcription factor LmMYB15 showed a significant correlation with CGA content, indicating its potential role in CGA biosynthesis. A yeast two-hybrid assay suggested that LmMYB15 functions as a transcriptional activator. Overexpression of LmMYB15 in tobacco led to increased accumulation of CGA compared to those in wild-type leaves. To elucidate its functional mechanism, genome-wide DAP-seq was employed and identified the conserved binding motifs of LmMYB15, that is [(C/T) (C/T) (C/T) ACCTA(C/A) (C/T) (A/T)], as well as its direct downstream target genes, including 4CL, MYB3, MYB4, KNAT6/7, IAA26, and ETR2. Subsequently, yeast one-hybrid and dual-luciferase reporter assays verified that LmMYB15 could bind and activate the promoters of 4CL, MYB3 and MYB4, thereby facilitating CGA biosynthesis and phenylpropanoid metabolism. Our findings provide a new track for breeding strategies aiming to enhance CGA content in L. macranthoides that can significantly contribute to better mechanical properties.

Phenolic composition and cell-based biological activities of ten coloured potato peels (Solanum tuberosum L.)

The present study provides an in-depth characterisation of the non-anthocyanin and anthocyanin phenolic compounds of potato peels from ten coloured potato varieties. Furthermore, the underexplored bioactive potential (antioxidant, cytotoxic and anti-inflammatory capacities) of the studied peels is comprehensively analysed. Among non-anthocyanin phenolics, caffeic and a caffeoylquinic acid were found in the highest concentrations in all samples, which also showed the presence of O-glycosylated flavonol derivatives and polyamine derivatives. Acylated anthocyanins were identified in red and purple varieties, being pelargonidin, peonidin, and malvidin the most prominent aglycones. All samples revealed antioxidant and antitumor activities, and no toxic effect. The extract of the Rosemary variety presented the best antioxidant and antitumor outcomes and was the only sample to reveal anti-inflammatory activity. These results are valuable for the food-industry by adding value to an important bio-residue, particularly concerning its potential as natural ingredients in novel food and pharmaceutical formulations.

Auxin-Responsive R2R3-MYB Transcription Factors HcMYB1 and HcMYB2 Activate Volatile Biosynthesis in Hedychium coronarium Flowers

Auxin, an important plant hormone, induces the biosynthesis of various secondary metabolites by modulating the expression of auxin-responsive genes. In the ornamental plant Hedychium coronarium, linalool and methyl benzoate are biosynthesized by the terpene synthase (TPS) HcTPS5 and the benzoic/salicylic acid methyltransferase (BSMT) HcBSMT2, respectively. However, the transcriptional regulation of this process remains unclear. Here, we identified and functionally characterized the R2R3-MYB transcription factors HcMYB1 and HcMYB2 in regulating the biosynthesis of these floral aroma compounds. HcMYB1 and HcMYB2 are specifically expressed in flowers, their expression is correlated with the emission of volatile compounds in flowers, and is induced by auxin. Moreover, HcMYB1 and HcMYB2 interact with the HcBSMT2 promoter region. HcMYB2 activates the expression of the linalool synthase gene HcTPS5. In flowers with HcMYB1 or HcMYB2 silenced, the levels of floral scent compounds were significantly reduced, and HcBSMT2 and HcTPS5 were downregulated compared with the wild type. Moreover, HcMYB1 form protein-protein interaction with key scent-related HcIAA4 protein to regulate floral aroma production. Taken together, these results indicate that HcMYB1 and HcMYB2 play crucial roles in regulating the formation of scent compounds in Hedychium coronarium (H. coronarium) flowers in response to auxin signaling.

MYB57 transcriptionally regulates MAPK11 to interact with PAL2;3 and modulate rice allelopathy

Rice allelopathy is a natural method of weed control that is regarded as an eco-friendly practice in agroecology. The allelopathic potential of rice is regulated by various genes, including those that encode transcription factors. Our study characterized a MYB transcription factor, OsMYB57, to explore its role in the regulation of rice allelopathy. Increasing the expression of OsMYB57 in rice using the transcription activator VP64 resulted in increased inhibitory ratios against barnyardgrass. The gene expression levels of OsPAL, OsC4H, OsOMT, and OsCAD from the phenylpropanoid pathway were also up-regulated, and the content of l-phenylalanine increased. Chromatin immunoprecipitation incorporated with HiSeq demonstrated that OsMYB57 transcriptionally regulated a mitogen-activated protein kinase (OsMAPK11); in addition, OsMAPK11 interacted with OsPAL2;3. The expression of OsPAL2;3was higher in the allelopathic rice PI312777 than in the non-allelopathic rice Lemont, and OsPAL2;3 was negatively regulated by Whirly transcription factors. Moreover, microbes with weed-suppression potential, including Penicillium spp. and Bacillus spp., were assembled in the rhizosphere of the rice accession Kitaake with increased expression of OsMYB57, and were responsible for phenolic acid induction. Our findings suggest that OsMYB57 positively regulates rice allelopathy, providing an option for the improvement of rice allelopathic traits through genetic modification.

Gene expression responses of tomato inoculated with Pectobacterium carotovorum subsp. carotovorum

Defense responses of tomato (Solanum lycopersicum L.) against attack by Pectobacterium carotovorum subsp. carotovorum (Pcc), the causal agent of soft rot diseases, were studied. The expression of some tomato defense genes were evaluated by real‐time PCR quantification analysis, 24 and 72 hr after actively growing tomato plants were inoculated with Pcc. These included: MYB transcriptor factor, ethylene response element‐binding protein, suppressor of the G2 allele of Skp1, cytochrome P450, small Sar1 GTPase, hydroxycinnamoyl‐CoA:quinate hydroxycinnamoyl transferase, pathogenesis‐related protein 1a, endo‐1,3‐beta‐glucanase, chitinase, proteinase inhibitor, defensin, CC‐NBS‐LRR resistance protein, and phenylalanine ammonia lyase. The results showed dynamic transcriptomic changes, with transcripts exhibiting different expression kinetics at 24 and 72 hr to confer resistance to tomato against Pcc infection.

StMYB44 negatively regulates anthocyanin biosynthesis at high temperatures in tuber flesh of potato

High temperatures are known to reduce anthocyanin accumulation in a number of diverse plant species. In potato (Solanum tuberosum L.), high temperature significantly reduces tuber anthocyanin pigment content. However, the mechanism of anthocyanin biosynthesis in potato tuber under heat stress remains unknown. Here we show that high temperature causes reduction of anthocyanin biosynthesis in both potato tuber skin and flesh, with white areas forming between the vasculature and periderm. Heat stress reduced the expression of the R2R3 MYB transcription factors (TFs) StAN1 and StbHLH1, members of the transcriptional complex responsible for coordinated regulation of the skin and flesh pigmentation, as well as anthocyanin biosynthetic pathway genes in white regions. However, the core phenylpropanoid pathway, lignin, and chlorogenic acid (CGA) pathway genes were up-regulated in white areas, suggesting that suppression of the anthocyanin branch may result in re-routing phenylpropanoid flux into the CGA or lignin biosynthesis branches. Two R2R3 MYB TFs, StMYB44-1 and StMYB44-2, were highly expressed in white regions under high temperature. In transient assays, StMYB44 represses anthocyanin accumulation in leaves of Nicotiana tabacum and N. benthamiana by directly suppressing the activity of the dihydroflavonol reductase (DFR) promoter. StMYB44-1 showed stronger repressive capacity than StMYB44-2, with both predicted proteins containing the repression-associated EAR motif with some variation. StMYB44-1 conferred repression without a requirement for a basic helix-loop-helix (bHLH) partner, suggesting a different repression mechanism from that of reported anthocyanin repressors. We propose that temperature-induced reduction of anthocyanin accumulation in potato flesh is caused by down-regulation of the activating anthocyanin regulatory complex, by enhancing the expression of flesh-specific StMYB44 and alteration of phenylpropanoid flux.

Combined effect of ultrasound treatment and exogenous phytohormones on the accumulation of bioactive compounds in broccoli florets

Postharvest treatments such as wounding, ultrasound (US) and the exogenous application of ethylene (ET) and methyl jasmonate (MJ) have been studied as an effective tool to improve the content of secondary metabolites in fresh produce. The present study evaluated the immediate and late response (storage for 72 h at 15 °C) to US treatment (20 min, frequency 24 kHz, amplitude 100 μm) alone and combined with exogenous MJ (250 ppm) and/or ET (1000 ppm) on glucosinolates, isothiocyanates, phenolic compounds and ascorbic acid content in broccoli florets. US treatment increased the extractability of glucosinolates [glucoraphanin (795%), 4-hydroxy glucobrassicin (153%), glucobrassicin (78.6%)] and phenolics [1-sinapoyl-2-feruloylgentiobiose (57.23%)] as compared with the control (CT). The combined application of MJ and US in broccoli florets, induced a synergistic effect on the accumulation of 4-hydroxy glucobrassicin (187.1%), glucoerucin (111.92%), gluconasturtiin (755.9%), neoglucobrassicin (232.8%), 3-O-caffeoylquinic acid (73.4%), 1-sinapoyl-2-ferulolylgentiobiose (56.0%), and 1,2,2-trisinapoylgentiobiose (136.7%) at 72 h of storage. Interestingly, when the three stressors were applied together the synergistic effect of US + MJ observed on the accumulation of glucosinolates and phenolics was repressed. In general, the ascorbic acid content was not affected by US treatment and decreased in most samples during storage. However, when MJ + ET were applied, the content of total ascorbic acid was significantly reduced in CT + MJ + ET and US + MJ + ET samples after 72 h of storage by 53.4% and 86.6%, respectively, as compared with CT 0 h samples. Based on the results herein obtained, the application of US can be an effective tool to enhance the extractability of certain glucocosinolate and phenolic compounds in broccoli. Moreover, due to the synergistic effect observed on the accumulation of bioactive compounds, the combined application of US and MJ could be a practical approach to yield higher levels of glucosinolates and phenolic compounds in broccoli during storage.

Subfunctionalization of duplicate MYB genes in Solanum commersonii generated the cold-induced ScAN2 and the anthocyanin regulator ScAN1

Wild potato species are useful sources of allelic diversity and loci lacking in the cultivated potato. In these species, the presence of anthocyanins in leaves has been associated with a greater tolerance to cold stress. However, the molecular mechanisms that allow potatoes to withstand cold exposure remain unclear. Here, we show that the expression of AN2, a MYB transcription factor, is induced by low temperatures in wild, cold-tolerant Solanum commersonii, and not in susceptible Solanum tuberosum varieties. We found that AN2 is a paralog of the potato anthocyanin regulator AN1, showing similar interaction ability with basic helix-loop-helix (bHLH) co-partners. Their sequence diversity resulted in a different capacity to promote accumulation of phenolics when tested in tobacco. Indeed, functional studies demonstrated that AN2 is less able to induce anthocyanins than AN1, but nevertheless it has a strong ability to induce accumulation of hydroxycinnamic acid derivatives. We propose that the duplication of R2R3 MYB genes resulted in subsequent subfunctionalization, where AN1 specialized in anthocyanin production and AN2 conserved the ability to respond to cold stress, inducing mainly the synthesis of hydroxycinnamic acid derivatives. These results contribute to understanding the evolutionary significance of gene duplication on phenolic compound regulation.

A comparative transcriptome analysis of a wild purple potato and its red mutant provides insight into the mechanism of anthocyanin transformation

In this study, a red mutant was obtained through in vitro regeneration of a wild purple potato. High-performance liquid chromatography and Mass spectrometry analysis revealed that pelargonidin-3-O-glucoside and petunidin-3-O-glucoside were main anthocyanins in the mutant and wild type tubers, respectively. In order to thoroughly understand the mechanism of anthocyanin transformation in two materials, a comparative transcriptome analysis of the mutant and wild type was carried out through high-throughput RNA sequencing, and 295 differentially expressed genes (DEGs) were obtained. Real-time qRT-PCR validation of DEGs was consistent with the transcriptome date. The DEGs mainly influenced biological and metabolic pathways, including phenylpropanoid biosynthesis and translation, and biosynthesis of flavone and flavonol. In anthocyanin biosynthetic pathway, the analysis of structural genes expressions showed that three genes, one encoding phenylalanine ammonia-lyase, one encoding 4-coumarate-CoA ligase and one encoding flavonoid 3′,5′-hydroxylasem were significantly down-regulated in the mutant; one gene encoding phenylalanine ammonia-lyase was significantly up-regulated. Moreover, the transcription factors, such as bZIP family, MYB family, LOB family, MADS family, zf-HD family and C2H2 family, were significantly regulated in anthocyanin transformation. Response proteins of hormone, such as gibberellin, abscisic acid and brassinosteroid, were also significantly regulated in anthocyanin transformation. The information contributes to discovering the candidate genes in anthocyanin transformation, which can serve as a comprehensive resource for molecular mechanism research of anthocyanin transformation in potatoes.

Potato miR828 Is Associated With Purple Tuber Skin and Flesh Color

Anthocyanins are plant pigments responsible for the colors of many flowers, fruits and storage organs and have roles in abiotic and biotic stress resistance. Anthocyanins and polyphenols are bioactive compounds in plants including potato (Solanum tuberosum L.) which is the most important non-cereal crop in the world, cultivated for its tubers rich in starch and nutrients. The genetic regulation of the flavonoid biosynthetic pathway is relatively well known leading to the formation of anthocyanins. However, our knowledge of post-transcriptional regulation of anthocyanin biosynthesis is limited. There is increasing evidence that micro RNAs (miRNAs) and other small RNAs can regulate the expression level of key factors in anthocyanin production. In this study we have found strong associations between the high levels of miR828, TAS4 D4(-) and purple/red color of tuber skin and flesh. This was confirmed not only in different cultivars but in pigmented and non-pigmented sectors of the same tuber. Phytochemical analyses verified the levels of anthocyanins and polyphenols in different tissues. We showed that miR828 is able to direct cleavage of the RNA originating from Trans-acting siRNA gene 4 (TAS4) and initiate the production of phased small interfering RNAs (siRNAs) whose production depends on RNA-dependent RNA polymerase 6 (RDR6). MYB transcription factors were predicted as potential targets of miR828 and TAS4 D4(-) and their expression was characterized. MYB12 and R2R3-MYB genes showed decreased expression levels in purple skin and flesh in contrast with high levels of small RNAs in the same tissues. Moreover, we confirmed that R2R3-MYB and MYB-36284 are direct targets of the small RNAs. Overall, this study sheds light on the small RNA directed anthocyanin regulation in potato, which is an important member of the Solanaceae family.

Regulation of chlorogenic acid biosynthesis by hydroxycinnamoyl CoA quinate hydroxycinnamoyl transferase in Lonicera japonica

For many centuries, Lonicera japonica has been used as an effective herb for the treatment of inflammation and swelling because of the presence of bioactive components such as chlorogenic acid (CGA). To clarify the relationship between L. japonica hydroxycinnamoyl CoA quinate hydroxycinnamoyl transferase (HQT) gene expression and CGA content, an HQT eukaryotic expression system was constructed using Gateway cloning. L. japonica callus transformed with HQT was obtained using Agrobacterium tumefaciens-mediated transformation. We found a positive correlation between CGA content, determined by High-Performance Liquid Chromatography (HPLC), and the expression of HQT, analyzed by semi-quantitative RT-PCR. This study demonstrates that the HQT gene positively regulates CGA synthesis and lays the foundation for further study into enhancing efficacious components of medicinal plants.

Hydroxycinnamic acids in cooked potato tubers from Solanum tuberosum group Phureja

Hydroxycinnamic acids are phenolic compounds and are considered to have health promotion properties due to their antioxidant activity. Potato tubers of 113 genotypes of Solanum tuberosum group Phureja belonging to the Colombian Central Collection, landraces of potatoes, and commercial cultivars were evaluated for their hydroxycinnamic acids content. The composition of these compounds was analyzed using cooked tubers in two different agro-climatic conditions. The genotypes were analyzed for chlorogenic acid, neo-chlorogenic acid, crypto-chlorogenic acid, and caffeic acid by ultrahigh-performance liquid chromatography (UHPLC). Chlorogenic acid was the major representative and varied between 0.77 to 7.98 g kg-1 DW (dry weight) followed by crypto-chlorogenic acid (from 0.09 to 1.50 g kg-1 DW). Under moorland agro-climatic conditions even though the chlorogenic acid levels increased with respect to flatland agro-climatic conditions, the related isomer neo-chlorogenic acid decreased as compared to flatland conditions. The correlation between chlorogenic acid with the isomers, and with caffeic acid was positive. This study demonstrated that there is a wide variation in hydroxycinnamic acids contents in the germplasm studied, which can be exploited in breeding programs to contribute to human health.

Chlorogenic acid, anthocyanin and flavan-3-ol biosynthesis in flesh and skin of Andean potato tubers (Solanum tuberosum subsp. andigena)

Natural variation of Andean potato was used to study the biosynthesis of phenolic compounds. Levels of phenolic compounds and corresponding structural gene transcripts were examined in flesh and skin of tubers. Phenolic acids, mainly chlorogenic acid (CGA), represent the major compounds, followed by anthocyanins and flavan-3-ols. High-anthocyanin varieties have high levels of CGA. Both metabolite and transcript levels were higher in skin than in flesh and showed a good correspondence. Two hydroxycinnamoyl-CoA transferases (HCT/HQT) have been involved in CGA production, of which HCT reflects CGA levels. Catechin was found in pigmented tissues whereas epicatechin was restricted to tuber skin. Transcripts of leucoanthocyanidin reductase (LCR), which generates catechin, could not be detected. Anthocyanidin reductase (ANR) transcripts, the enzyme responsible for epicatechin production, showed similar levels among samples. These data suggest that the biosynthesis of flavan-3-ols in potato tuber would require ANR but not LCR and that an epimerization process is involved.

Phenylpropanoids Accumulation in Eggplant Fruit: Characterization of Biosynthetic Genes and Regulation by a MYB Transcription Factor

Phenylpropanoids are major secondary metabolites in eggplant (Solanum melongena) fruits. Chlorogenic acid (CGA) accounts for 70-90% of total phenolics in flesh tissues, while anthocyanins are mainly present in the fruit skin. As a contribution to the understanding of the peculiar accumulation of these health-promoting metabolites in eggplant, we report on metabolite abundance, regulation of CGA and anthocyanin biosynthesis, and characterization of candidate CGA biosynthetic genes in S. melongena. Higher contents of CGA, Delphinidin 3-rutinoside, and rutin were found in eggplant fruits compared to other tissues, associated to an elevated transcript abundance of structural genes such as PAL, HQT, DFR, and ANS, suggesting that active in situ biosynthesis contributes to anthocyanin and CGA accumulation in fruit tissues. Putative orthologs of the two CGA biosynthetic genes PAL and HQT, as well as a variant of a MYB1 transcription factor showing identity with group six MYBs, were isolated from an Occidental S. melongena traditional variety and demonstrated to differ from published sequences from Asiatic varieties. In silico analysis of the isolated SmPAL1, SmHQT1, SmANS, and SmMyb1 promoters revealed the presence of several Myb regulatory elements for the biosynthetic genes and unique elements for the TF, suggesting its involvement in other physiological roles beside phenylpropanoid biosynthesis regulation. Transient overexpression in Nicotiana benthamiana leaves of SmMyb1 and of a C-terminal SmMyb1 truncated form (SmMyb1Δ9) resulted in anthocyanin accumulation only of SmMyb1 agro-infiltrated leaves. A yeast two-hybrid assay confirmed the interaction of both SmMyb1 and SmMyb1Δ9 with an anthocyanin-related potato bHLH1 TF. Interestingly, a doubled amount of CGA was detected in both SmMyb1 and SmMyb1Δ9 agro-infiltrated leaves, thus suggesting that the N-terminal region of SmMyb1 is sufficient to activate its synthesis. These data suggest that a deletion of the C-terminal region of SmMyb1 does not limit its capability to regulate CGA accumulation, but impairs anthocyanin biosynthesis. To our knowledge, this is the first study reporting a functional elucidation of the role of the C-term conserved domain in MYB activator proteins.

Comparative Transcriptome Analysis of White and Purple Potato to Identify Genes Involved in Anthocyanin Biosynthesis

INTRODUCTION

The potato (Solanum tuberosum) cultivar 'Xin Daping' is tetraploid with white skin and white flesh, while the cultivar 'Hei Meiren' is also tetraploid with purple skin and purple flesh. Comparative transcriptome analysis of white and purple cultivars was carried out using high-throughput RNA sequencing in order to further understand the mechanism of anthocyanin biosynthesis in potato.

METHODS AND RESULTS

By aligning transcript reads to the recently published diploid potato genome and de novo assembly, 209 million paired-end Illumina RNA-seq reads from these tetraploid cultivars were assembled on to 60,930 transcripts, of which 27,754 (45.55%) are novel transcripts and 9393 alternative transcripts. Using a comparison of the RNA-sequence datasets, multiple versions of the genes encoding anthocyanin biosynthetic steps and regulatory transcription factors were identified. Other novel genes potentially involved in anthocyanin biosynthesis in potato tubers were also discovered. Real-time qPCR validation of candidate genes revealed good correlation with the transcriptome data. SNPs (Single Nucleotide Polymorphism) and indels were predicted and validated for the transcription factors MYB AN1 and bHLH1 and the biosynthetic gene anthocyanidin 3-O-glucosyltransferase (UFGT).

CONCLUSIONS

These results contribute to our understanding of the molecular mechanism of white and purple potato development, by identifying differential responses of biosynthetic gene family members together with the variation in structural genes and transcription factors in this highly heterozygous crop. This provides an excellent platform and resource for future genetic and functional genomic research.

Chlorogenic Acid Biosynthesis Appears Linked with Suberin Production in Potato Tuber (Solanum tuberosum)

Potato (Solanum tuberosum L.) is a good source of dietary antioxidants. Chlorogenic acid (CGA) and caffeic acid (CA) are the most abundant phenolic acid antioxidants in potato and are formed by the phenylpropanoid pathway. A number of CGA biosynthetic routes that involve hydroxycinnamoyl-CoA quinate hydroxycinnamoyl transferase (HQT) and/or hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (HCT) have been proposed, but little is known about their path in potato. CA production requires a caffeoyl shikimate esterase (CSE), and CA serves as a substrate of lignin precursor ferulic acid via the action of caffeic/5-hydroxyferulic acid O-methyltransferase (COMT I). CGA is precursor of caffeoyl-CoA and, via caffeoyl-CoA O-methyltransferase (CCoAOMT), of feruloyl-CoA. Feruloyl-CoA is required for lignin and suberin biosynthesis, crucial for tuber development. Here, metabolite and transcript levels of the mentioned and related enzymes, such as cinnamate 4-hydroxylase (C4H), were determined in the flesh and skin of fresh and stored tubers. Metabolite and transcript levels were higher in skin than in flesh, irrespective of storage. CGA and CA production appear to occur via p-coumaroyl-CoA, using HQT and CSE, respectively. HCT is likely involved in CGA remobilization toward suberin. The strong correlation between CGA and CA, the correspondence with C4H, HQT, CCoAOMT2, and CSE, and the negative correlation of HCT and COMT I in potato tubers suggest a major flux toward suberin.

Synthesis and regulation of chlorogenic acid in potato: Rerouting phenylpropanoid flux in HQT-silenced lines

Chlorogenic acid (CGA) is the major phenolic sink in potato tubers and can constitute over 90% of total phenylpropanoids. The regulation of CGA biosynthesis in potato and the role of the CGA biosynthetic gene hydroxycinnamoyl CoA:quinate hydroxycinnamoyl transferase (HQT) was characterized. A sucrose induced accumulation of CGA correlated with the increased expression of phenylalanine ammonia-lyase (PAL) rather than HQT. Transient expression of the potato MYB transcription factor StAN1 (anthocyanin 1) in tobacco increased CGA. RNAi suppression of HQT resulted in over a 90% reduction in CGA and resulted in early flowering. The reduction in total phenolics and antioxidant capacity was less than the reduction in CGA, suggesting flux was rerouted into other phenylpropanoids. Network analysis showed distinct patterns in different organs, with anthocyanins and phenolic acids showing negative correlations in leaves and flowers and positive in tubers. Some flavonols increased in flowers, but not in leaves or tubers. Anthocyanins increased in flowers and showed a trend to increase in leaves, but not tubers. HQT suppression increased biosynthesis of caffeoyl polyamines, some of which are not previously reported in potato. Decreased PAL expression and enzyme activity was observed in HQT suppressed lines, suggesting the existence of a regulatory loop between CGA and PAL. Electrophysiology detected no effect of CGA suppression on potato psyllid feeding. Collectively, this research showed that CGA in potatoes is synthesized through HQT and HQT suppression altered phenotype and redirected phenylpropanoid flux.

MYB Transcription Factors as Regulators of Phenylpropanoid Metabolism in Plants

Phenylpropanoid-derived compounds represent a diverse family of secondary metabolites that originate from phenylalanine. These compounds have roles in plant growth and development, and in defense against biotic and abiotic stress. Many of these compounds are also beneficial to human health and welfare. V-myb myeloblastosis viral oncogene homolog (MYB) proteins belong to a large family of transcription factors and are key regulators of the synthesis of phenylpropanoid-derived compounds. This review summarizes the current understanding of MYB proteins and their roles in the regulation of phenylpropanoid metabolism in plants.

Location of chlorogenic acid biosynthesis pathway and polyphenol oxidase genes in a new interspecific anchored linkage map of eggplant

BACKGROUND

Eggplant is a powerful source of polyphenols which seems to play a key role in the prevention of several human diseases, such as cancer and diabetes. Chlorogenic acid is the polyphenol most present in eggplant, comprising between the 70% and 90% of the total polyphenol content. Introduction of the high chlorogenic acid content of wild relatives, such as S. incanum, into eggplant varieties will be of great interest. A potential side effect of the increased level polyphenols could be a decrease on apparent quality due to browning caused by the polyphenol oxidase enzymes mediated oxidation of polyphenols. We report the development of a new interspecific S. melongena × S. incanum linkage map based on a first backcross generation (BC1) towards the cultivated S. melongena as a tool for introgressing S. incanum alleles involved in the biosynthesis of chlorogenic acid in the genetic background of S. melongena.

RESULTS

The interspecific genetic linkage map of eggplant developed in this work anchor the most informative previously published genetic maps of eggplant using common markers. The 91 BC1 plants of the mapping population were genotyped with 42 COSII, 99 SSRs, 88 AFLPs, 9 CAPS, 4 SNPs and one morphological polymorphic markers. Segregation marker data resulted in a map encompassing 1085 cM distributed in 12 linkage groups. Based on the syntheny with tomato, the candidate genes involved in the core chlorogenic acid synthesis pathway in eggplant (PAL, C4H, 4CL, HCT, C3'H, HQT) as well as five polyphenol oxidase (PPO1, PPO2, PPO3, PPO4, PPO5) were mapped. Except for 4CL and HCT chlorogenic acid genes were not linked. On the contrary, all PPO genes clustered together. Candidate genes important in domestication such as fruit shape (OVATE, SISUN1) and prickliness were also located.

CONCLUSIONS

The achievements in location of candidate genes will allow the search of favorable alleles employing marker-assisted selection in order to develop new varieties with higher chlorogenic content alongside a lower polyphenol oxidase activity. This will result into an enhanced product showing a lower fruit flesh browning with improved human health properties.

High AN1 variability and interaction with basic helix-loop-helix co-factors related to anthocyanin biosynthesis in potato leaves

AN1 is a regulatory gene that promotes anthocyanin biosynthesis in potato tubers and encodes a R2R3 MYB transcription factor. However, no clear evidence implicates AN1 in anthocyanin production in leaves, where these pigments might enhance environmental stress tolerance. In our study we found that AN1 displays intraspecific sequence variability in both coding/non-coding regions and in the promoter, and that its expression is associated with high anthocyanin content in leaves of commercial potatoes. Expression analysis provided evidence that leaf pigmentation is associated to AN1 expression and that StJAF13 acts as putative AN1 co-regulator for anthocyanin gene expression in leaves of the red leaf variety 'Magenta Love,' while a concomitant expression of StbHLH1 may contribute to anthocyanin accumulation in leaves of 'Double Fun.' Yeast two-hybrid experiments confirmed that AN1 interacts with StbHLH1 and StJAF13 and the latter interaction was verified and localized in the cell nucleus by bimolecular fluorescence complementation assays. In addition, transgenic tobacco (Nicotiana tabacum) overexpressing a combination of either AN1 with StJAF13 or AN1 with StbHLH1 showed deeper purple pigmentation with respect to AN1 alone. This further confirmed AN1/StJAF13 and AN1/StbHLH1 interactions. Our findings demonstrate that the classical loci identified for potato leaf anthocyanin accumulation correspond to AN1 and may represent an important step to expand our knowledge on the molecular mechanisms underlying anthocyanin biosynthesis in different plant tissues.

Cloning and characterization of a potato StAN11 gene involved in anthocyanin biosynthesis regulation

Anthocyanins are a class of products of plant secondary metabolism and are responsible for tubers color in potato. The biosynthesis of anthocyanins is a complex biological process, in which multiple genes are involved including structural genes and regulatory genes. In this study, StAN11, a WD40-repeat gene, was cloned from potato cultivar Chieftain (Solanum tuberosum L.). StAN11 (HQ599506) contained no intron and its open reading frame (ORF) was 1,029 bp long, encoding a putative protein of 342 amino acids. In order to verify its role in anthocyanin biosynthesis, StAN11 was inserted behind the CaMV-35S promoter of pCMBIA1304 and the recombination vector was introduced into the potato cultivar Désirée plants by Agrobacterium-mediated transformation. The color of transgenic tuber skin was significantly deepened, compared to the wild-type control, which was highly consistent with the accumulation of anthocyanin and expression of StAN11 in transgenic lines tuber skin. Further analysis on the expression of Flavonone-3-hydroxylase (F3H), Dihydroflavonol reductase (DFR), Anthocyanidin synthase (ANS), and Flavonoid 3-O-glucosyl transferase (3GT) in transgenic plants revealed that only DFR was upregulated. This result suggested that StAN11 regulated anthocyanin biosynthesis in potato by controlling DFR expression and accumulation of anthocyanin could be increased through overexpression of StAN11 in the tubers with the genetic background of anthocyanin biosynthesis.

Transcription factors, sucrose, and sucrose metabolic genes interact to regulate potato phenylpropanoid metabolism

Much remains unknown about how transcription factors and sugars regulate phenylpropanoid metabolism in tuber crops like potato (Solanum tuberosum). Based on phylogeny and protein similarity to known regulators of phenylpropanoid metabolism, 15 transcription factors were selected and their expression was compared in white, yellow, red, and purple genotypes with contrasting phenolic and anthocyanin profiles. Red and purple genotypes had increased phenylalanine ammonia lyase (PAL) enzyme activity, markedly higher levels of phenylpropanoids, and elevated expression of most phenylpropanoid structural genes, including a novel anthocyanin O-methyltransferase. The transcription factors Anthocyanin1 (StAN1), basic Helix Loop Helix1 (StbHLH1), and StWD40 were more strongly expressed in red and purple potatoes. Expression of 12 other transcription factors was not associated with phenylpropanoid content, except for StMYB12B, which showed a negative relationship. Increased expression of AN1, bHLH1, and WD40 was also associated with environmentally mediated increases in tuber phenylpropanoids. Treatment of potato plantlets with sucrose induced hydroxycinnamic acids, flavonols, anthocyanins, structural genes, AN1, bHLH1, WD40, and genes encoding the sucrose-hydrolysing enzymes SUSY1, SUSY4, and INV2. Transient expression of StAN1 in tobacco leaves induced bHLH1, structural genes, SUSY1, SUSY4, and INV1, and increased phenylpropanoid amounts. StAN1 infiltration into tobacco leaves decreased sucrose and glucose concentrations. In silico promoter analysis revealed the presence of MYB and bHLH regulatory elements on sucrolytic gene promoters and sucrose-responsive elements on the AN1 promoter. These findings reveal an interesting dynamic between AN1, sucrose, and sucrose metabolic genes in modulating potato phenylpropanoids.

GMOs in animal agriculture: time to consider both costs and benefits in regulatory evaluations

In 2012, genetically engineered (GE) crops were grown by 17.3 million farmers on over 170 million hectares. Over 70% of harvested GE biomass is fed to food producing animals, making them the major consumers of GE crops for the past 15 plus years. Prior to commercialization, GE crops go through an extensive regulatory evaluation. Over one hundred regulatory submissions have shown compositional equivalence, and comparable levels of safety, between GE crops and their conventional counterparts. One component of regulatory compliance is whole GE food/feed animal feeding studies. Both regulatory studies and independent peer-reviewed studies have shown that GE crops can be safely used in animal feed, and rDNA fragments have never been detected in products (e.g. milk, meat, eggs) derived from animals that consumed GE feed. Despite the fact that the scientific weight of evidence from these hundreds of studies have not revealed unique risks associated with GE feed, some groups are calling for more animal feeding studies, including long-term rodent studies and studies in target livestock species for the approval of GE crops. It is an opportune time to review the results of such studies as have been done to date to evaluate the value of the additional information obtained. Requiring long-term and target animal feeding studies would sharply increase regulatory compliance costs and prolong the regulatory process associated with the commercialization of GE crops. Such costs may impede the development of feed crops with enhanced nutritional characteristics and durability, particularly in the local varieties in small and poor developing countries. More generally it is time for regulatory evaluations to more explicitly consider both the reasonable and unique risks and benefits associated with the use of both GE plants and animals in agricultural systems, and weigh them against those associated with existing systems, and those of regulatory inaction. This would represent a shift away from a GE evaluation process that currently focuses only on risk assessment and identifying ever diminishing marginal hazards, to a regulatory approach that more objectively evaluates and communicates the likely impact of approving a new GE plant or animal on agricultural production systems.

In nutrition, can we "see" what is good for us?

The selection of foods to eat is a complex interplay of vision, taste, smell, and texture. In addition to micro- and macronutrients, plant-based foods also contain several classes of phytochemicals. In many cases, the phytochemicals account for the various colors of foods. Although aesthetically pleasing, the color of foods may mislead consumers as to their phytochemical content, which is particularly true with regard to polyphenols. Polyphenols are a broad class of compounds with antioxidant and other health benefits. Human vision is limited to a small window (390-765 nm) of the electromagnetic spectrum. Many important phytochemicals (e.g., vitamin C) have no absorbance in this range. Therefore, the human eye cannot directly judge the vitamin C content of foods. Being able to see in the ultraviolet range allows bees to locate the pollen-rich region of flowers, whereas pit vipers locate their prey by being able to "see" them in the infrared range. Assessing the impact of phytochemicals on human health depends on several factors. Colorless phytochemicals in unprocessed foods may be lost during the cooking process because no visual guide exists to ensure their retention. The molecular structures of phytochemicals influence the extent to which they are altered by cooking processes and the methods by which they are absorbed from the gastrointestinal tract. Extensive metabolism by phase I/II enzymes and by the gut microbiome may also create compounds that the eye is never allowed to appreciate.

Analysis of genetically modified red-fleshed apples reveals effects on growth and consumer attributes

Consumers of whole foods, such as fruits, demand consistent high quality and seek varieties with enhanced health properties, convenience or novel taste. We have raised the polyphenolic content of apple by genetic engineering of the anthocyanin pathway using the apple transcription factor MYB10. These apples have very high concentrations of foliar, flower and fruit anthocyanins, especially in the fruit peel. Independent lines were examined for impacts on tree growth, photosynthesis and fruit characteristics. Fruit were analysed for changes in metabolite and transcript levels. Fruit were also used in taste trials to study the consumer perception of such a novel apple. No negative taste attributes were associated with the elevated anthocyanins. Modification with this one gene provides near isogenic material and allows us to examine the effects on an established cultivar, with a view to enhancing consumer appeal independently of other fruit qualities.

Changes in potato phenylpropanoid metabolism during tuber development

Phenylpropanoid metabolite and transcript expression during different developmental stages were examined in field grown potatoes. Carbohydrate and shikimic acid metabolism was assessed to determine how tuber primary metabolism influences phenylpropanoid metabolism. Phenylpropanoid concentrations were highest in immature tubers, as were some transcript levels and enzyme activities including phenylalanine ammonia lyase (PAL). Phenylpropanoid concentration differences between mature and immature tubers varied by genotype, but in some cases were approximately three-fold. The most abundant phenylpropanoid was chlorogenic acid (5CGA), which decreased during tuber maturation. Hydroxycinnamoyl-CoA:quinate hydroxycinnamoyl transferase (HQT) transcripts were highly expressed relative to other phenylpropanoid genes, but were not well correlated with 5CGA concentrations (r = -0.16), whereas HQT enzyme activity was. In contrast to 5CGA, less abundant chlorogenic isomers increased during development. Concentrations of hydroxycinnamic acid amides were higher in immature tubers, as was expression of arginine- and ornithine decarboxylases. Expression of several genes involved in carbohydrate or shikimate metabolism, including sucrose synthase and DAHP, showed similar developmental patterns to phenylpropanoid pools, as did shikimate dehydrogenase enzyme activity. Sucrose, glucose and fructose concentrations were highest in immature tubers. Exogenous treatment of potatoes with sugars stimulated phenylpropanoid biosynthesis, suggesting sugars contribute to the higher phenylpropanoid concentrations in immature tubers. These changes in phenylpropanoid expression suggest the nutritional value of potatoes varies during development.

Altered leaf colour is associated with increased superoxide-scavenging activity in aureusidin-producing transgenic plants

The health-promoting property of diets rich in fruits and vegetables is based, in part, on the additive and synergistic effects of multiple antioxidants. In an attempt to further enhance food quality, we introduced into crops the capability to synthesize a yellow antioxidant, aureusidin, that is normally produced only by some ornamental plants. For this purpose, the snapdragon (Antirrhinum majus) chalcone 4'-O-glucosyltransferase (Am4'CGT) and aureusidin synthase (AmAs1) genes, which catalyse the synthesis of aureusidin from chalcone, were expressed in tobacco (Nicotiana tabacum) and lettuce (Lactuca sativa) plants that displayed a functionally active chalcone/flavanone biosynthetic pathway. Leaves of the resulting transgenic plants developed a yellow hue and displayed higher superoxide dismutase (SOD) inhibiting and oxygen radical absorbance capacity (ORAC) activities than control leaves. Our results suggest that the nutritional qualities of leafy vegetables can be enhanced through the introduction of aurone biosynthetic pathways.

Tastier and healthier alternatives to French fries

The effect of both the origin and shape of potato cuts on fry quality was investigated in this study. Linear strips from the inner core of tubers were compared to those from outer tissues, both before and after processing, and strips from either specific tissues or whole peeled tubers were also evaluated against ring-shaped cuts. Both strips and rings had 0.7 cm sides and, in most cases, a volume of 4.9 cm(3). They were analyzed for moisture content, antioxidants, asparagine, and reducing sugars. The material was then blanched, dipped in 0.5% disodium acid pyrophosphate and 0.3% glucose, dried at 77 degrees C, par-fried in soybean oil at 191 degrees C, and finish-fried at 168 degrees C. The fried product was analyzed for sensory characteristics and oil, salt, and acrylamide content. Our results showed that strips from the inner core absorbed 28% more oil and exhibited inferior sensory characteristics compared to strips from the outer parts. The extended drying and frying times needed to match the crispness and flavor of inner strips to those of regularly fried outer strips resulted in a further increased absorption of oil and, importantly, triggered a 163% increase in levels of the toxic Maillard reaction product acrylamide. Potato rings consisted of higher dry matter material, contained more antioxidants, and had a lower surface-to-volume ratio than the conventional linear strips. Upon processing, they also absorbed 22% less oil, contained 26% less salt, and displayed superior sensory properties. Thus, ring fries may represent an attractive alternative to French fries as processed staple food.

The sweet potato IbMYB1 gene as a potential visible marker for sweet potato intragenic vector system

MYB transcription factors play important roles in transcriptional regulation of many secondary metabolites including anthocyanins. We cloned the R2R3-MYB type IbMYB1 complementary DNAs from the purple-fleshed sweet potato (Ipomoea batatas L. cv Sinzami) and investigated the expression patterns of IbMYB1 gene with IbMYB1a and IbMYB1b splice variants in leaf and root tissues of various sweet potato cultivars by reverse transcription-polymerase chain reaction. The transcripts of IbMYB1 were predominantly expressed in the purple-fleshed storage roots and they were also detectable in the leaf tissues accumulating anthocyanin pigments. In addition, transcript levels of IbMYB1 gene were up-regulated by treatment with methyl jasmonate or salicylic acid in leaf and root tissues of cv. White Star. To set up the intragenic vector system in sweet potato, we first evaluated the utilization of the IbMYB1 gene as a visible selectable marker. The IbMYB1a was transiently expressed in tobacco leaves under the control of a constitutive cauliflower mosaic virus 35S promoter, a root-specific and sucrose-inducible sporamin promoter, and an oxidative stress-inducible sweet potato anionic peroxidase2 promoter. We also showed that overexpression of IbMYB1a induced massive anthocyanin pigmentation in tobacco leaves and up-regulated the transcript levels of the structural genes in anthocyanin biosynthetic pathway. Furthermore, high-performance liquid chromatography analysis revealed that the expression of IbMYB1a led to production of cyanidin as a major core molecule of anthocyanidins in tobacco leaves. These results suggest that the IbMYB1 gene can be applicable to a visible marker for sweet potato transformation with intragenic vectors, as well as the production of anthocyanin as important nutritive value in other plant species.

Flavonoid profiling and transcriptome analysis reveals new gene-metabolite correlations in tubers of Solanum tuberosum L

Anthocyanin content of potato tubers is a trait that is attracting increasing attention as the potential nutritional benefits of this class of compound become apparent. However, our understanding of potato tuber anthocyanin accumulation is not complete. The aim of this study was to use a potato microarray to investigate gene expression patterns associated with the accumulation of purple tuber anthocyanins. The advanced potato selections, CO97216-3P/PW and CO97227-2P/PW, developed by conventional breeding procedures, produced tubers with incomplete expression of tuber flesh pigmentation. This feature permits sampling pigmented and non-pigmented tissues from the same tubers, in essence, isolating the factors responsible for pigmentation from confounding genetic, environmental, and developmental effects. An examination of the transcriptome, coupled with metabolite data from purple pigmented sectors and from non-pigmented sectors of the same tuber, was undertaken to identify these genes whose expression correlated with elevated or altered polyphenol composition. Combined with a similar study using eight other conventional cultivars and advanced selections with different pigmentation, it was possible to produce a refined list of only 27 genes that were consistently differentially expressed in purple tuber tissues compared with white. Within this list are several new candidate genes that are likely to impact on tuber anthocyanin accumulation, including a gene encoding a novel single domain MYB transcription factor.

Barriers and paths to market for genetically engineered crops

Each year, billions of dollars are invested in efforts to improve crops through genetic engineering (GE). These activities have resulted in a surge of publications and patents on technologies and genes: a momentum in basic research that, unfortunately, is not sustained throughout the subsequent phases of product development. After more than two decades of intensive research, the market for transgenic crops is still dominated by applications of just a handful of methods and genes. This discrepancy between research and development reflects difficulties in understanding and overcoming seven main barriers-to-entry: (1) trait efficacy in the field, (2) critical product concepts, (3) freedom-to-operate, (4) industry support, (5) identity preservation and stewardship, (6) regulatory approval and (7) retail and consumer acceptance. In this review, I describe the various roadblocks to market for transgenic crops and also discuss methods and approaches on how to overcome these, especially in the United States.

Levels and Stability of Expression of Transgenes

It is well known that in a given cell, at a particular time, only a fraction of the entire genome is expressed. Expression of a gene, nuclear, or organellar starts with the onset of transcription and ends in the synthesis of the functional protein. The regulation of gene expression is a complex process that requires the coordinated activity of different proteins and nucleic acids that ultimately determine whether a gene is transcribed, and if transcribed, whether it results in the production of a protein that develops a phenotype. The same also holds true for transgenic crops, which lie at the very core of insert design.

There are multiple checkpoints at which the expression of a gene can be regulated and controlled. Much of the emphasis of studies related to gene expression has been on regulation of gene transcription, and a number of methods are used to effect the control of gene expression. Controlling transgene expression for a commercially valuable trait is necessary to capture its value. Many gene functions are either lethal or produce severe deformity (resulting in loss of value) if over-expressed. Thus, expression of a transgene at a particular site or in response to a particular elicitor is always desirable.

The potato developer (D) locus encodes an R2R3 MYB transcription factor that regulates expression of multiple anthocyanin structural genes in tuber skin

A dominant allele at the D locus (also known as I in diploid potato) is required for the synthesis of red and purple anthocyanin pigments in tuber skin. It has previously been reported that D maps to a region of chromosome 10 that harbors one or more homologs of Petunia an2, an R2R3 MYB transcription factor that coordinately regulates the expression of multiple anthocyanin biosynthetic genes in the floral limb. To test whether D acts similarly in tuber skin, RT-PCR was used to evaluate the expression of flavanone 3-hydroxylase (f3h), dihydroflavonol 4-reductase (dfr) and flavonoid 3',5'-hydroxylase (f3'5'h). All three genes were expressed in the periderm of red- and purple-skinned clones, while dfr and f3'5'h were not expressed, and f3h was only weakly expressed, in white-skinned clones. A potato cDNA clone with similarity to an2 was isolated from an expression library prepared from red tuber skin, and an assay developed to distinguish the two alleles of this gene in a diploid potato clone known to be heterozygous Dd. One allele was observed to cosegregate with pigmented skin in an F(1) population of 136 individuals. This allele was expressed in tuber skin of red- and purple-colored progeny, but not in white tubers, while other parental alleles were not expressed in white or colored tubers. The allele was placed under the control of a doubled 35S promoter and transformed into the light red-colored cultivar Désirée, the white-skinned cultivar Bintje, and two white diploid clones known to lack the functional allele of D. Transformants accumulated pigment in tuber skin, as well as in other tissues, including young foliage, flower petals, and tuber flesh.