Accumulation of anthocyanins in tomato skin extends shelf life

Tomato pomace food waste from different variants as a high antioxidant potential resource

Pomaces obtained from three San Marzano tomato genotypes including the wild type (WT), Sun Black (SB), and colorless fruit epidermis (CL) were dried at 50 °C and analyzed for nutritional composition, total polyphenol (TPC), flavonoid (TFC) content, polyphenol qualitative profile, total antioxidant capacity (TAC), and antimicrobial activity. Commercial dried tomato powder (CTRP) was included as a control. No differences were detected nutritionally, in TPC and antimicrobial activity, but significant changes were observed for TFC and TAC, underlying variation in the phenolic profile. SB pomace (SBP) had the highest TFC and TAC. LC-HRMS analysis showed a flavonoid-enriched profile in SBP besides the exclusive presence of anthocyanins, with petanin and negretein as the most abundant. Among flavonoids, quercetin-hexose-deoxyhexose-pentose, naringenin, and rutin were the major. Overall, we showed the potential of dried tomato pomace, especially SBP, as an extremely valuable waste product to be transformed into a functional ingredient, reducing the food industry waste.

Genetic and Biotechnological Approaches to Improve Fruit Bioactive Content: A Focus on Eggplant and Tomato Anthocyanins

Anthocyanins are a large group of water-soluble flavonoid pigments. These specialized metabolites are ubiquitous in the plant kingdom and play an essential role not only in plant reproduction and dispersal but also in responses to biotic and abiotic stresses. Anthocyanins are recognized as important health-promoting and chronic-disease-preventing components in the human diet. Therefore, interest in developing food crops with improved levels and compositions of these important nutraceuticals is growing. This review focuses on work conducted to elucidate the genetic control of the anthocyanin pathway and modulate anthocyanin content in eggplant (Solanum melongena L.) and tomato (Solanum lycopersicum L.), two solanaceous fruit vegetables of worldwide relevance. While anthocyanin levels in eggplant fruit have always been an important quality trait, anthocyanin-based, purple-fruited tomato cultivars are currently a novelty. As detailed in this review, this difference in the anthocyanin content of the cultivated germplasm has largely influenced genetic studies as well as breeding and transgenic approaches to improve the anthocyanin content/profile of these two important solanaceous crops. The information provided should be of help to researchers and breeders in devising strategies to address the increasing consumer demand for nutraceutical foods.

In pursuit of purple: anthocyanin biosynthesis in fruits of the tomato clade

Over the past decade, progress has been made in the characterization of anthocyanin synthesis in fruits of plants belonging to the tomato clade. The genomic elements underlying the activation of the process were identified, providing the basis for understanding how the pathway works in these species. In this review we explore the genetic mechanisms that have been characterized to date, and detail the various wild relatives of the tomato, which have been crucial for recovering ancestral traits that were probably lost during evolution from green-purple to yellow and red tomatoes. This knowledge should help developing strategies to further enhance the status of the commercial tomato lines on sale, based on both genome editing and breeding techniques.

Fruits from tomato carotenoid mutants have altered susceptibility to grey mold

The necrotrophic fungus Botritys cinerea takes advantage of the oxidative burst to facilitate tissue infection, leading to substantial losses during tomato postharvest. Tomato fruit is a source of carotenoids, pigments with a wide variety of isomeric configurations that determine their antioxidant capacity. Here, fruit susceptibility to B. cinerea was assessed in Micro-Tom Near Isogenic lines harboring mutations that alter the profile of carotenoids. Wound-inoculated fruit of the mutants Delta carotene (Del) and tangerine (t), which show large variety of carotenoids rather than the major accumulation of trans-lycopene, were less susceptible to the pathogen. Differences in susceptibility between the mutants were only observed in ripe fruit, after the formation of carotenoids, and they were associated with attenuation of damage caused by reactive oxygen species. The greater variety of carotenoid isomers, which in turn contributed to the greater lipophilic antioxidant capacity of fruit, was associated with the less susceptible mutants, Del and t. Together, our data reveals a potential activity of carotenoids in fruit defense, in addition to the well-known and widespread ecological role as attractors of seed dispersers.

Anthocyanins distribution, transcriptional regulation, epigenetic and post-translational modification in fruits

Anthocyanins have indispensable functions in plant resistance, human health, and fruit coloring, which arouse people's favorite. It has been reported that anthocyanins are widely found in fruits, and can be affected by numerous factors. In this review, we systematically summarize anthocyanin functions, classifications, distributions, biosynthesis, decoration, transportation, transcriptional regulation, DNA methylation, and post-translational regulation in fruits.

SlBBX20 attenuates JA signalling and regulates resistance to Botrytis cinerea by inhibiting SlMED25 in tomato

Jasmonic acid (JA) plays an important role in regulating plant growth and defence responses. Here, we show that a transcription factor that belongs to the B-box (BBX) family named SlBBX20 regulates resistance to Botrytis cinerea in tomato by modulating JA signalling. The response to JA was significantly suppressed when SlBBX20 was overexpressed in tomato. By contrast, the JA response was enhanced in SlBBX20 knockout lines. RNA sequencing analysis provided more evidence that SlBBX20 modulates the expression of genes that are involved in JA signalling. We found that SlBBX20 interacts with SlMED25, a subunit of the Mediator transcriptional co-activator complex, and prevents the accumulation of the SlMED25 protein and transcription of JA-responsive genes. JA contributes to the defence response against necrotrophic pathogens. Knocking out SlBBX20 or overexpressing SlMED25 enhanced tomato resistance to B. cinerea. The resistance was impaired when SlBBX20 was overexpressed in plants that also overexpressed SlMED25. These data show that SlBBX20 attenuates JA signalling by regulating SlMED25. Interestingly, in addition to developing enhanced resistance to B. cinerea, SlBBX20-KO plants also produced higher fruit yields. SlBBX20 is a potential target gene for efforts that aim to develop elite crop varieties using gene editing technologies.

Induced mutation in ELONGATED HYPOCOTYL5 abolishes anthocyanin accumulation in the hypocotyl of pepper

The causal gene, CaHY5 of a chemical induced green-hypocotyl mutant was identified by molecular mapping. CaHY5 regulates anthocyanin accumulation by directly binding to the promoter of genes in anthocyanin pathway. Morphological markers at seedling stage are useful indicators for F₁ hybrid seeds screening. Pepper is a worldwide vegetable with diverse uses, and F₁ hybrids are popular in the pepper industry. Hypocotyl color is a useful marker to identify F₁ hybrid seeds. However, most pepper accessions have purple hypocotyl caused by anthocyanin accumulation, while green hypocotyl pepper accessions are rare. In this study, we identified a green hypocotyl mutant (e1898) from a pepper ethylmethanesulfonate (EMS) mutant library. By combining bulked segregant RNA-seq (BSR), genome resequencing and recombinant analysis, it was found that CaHY5 is the causal gene of this mutant. Virus-induced gene silencing (VIGS) of CaHY5 resulted in the decrease of anthocyanin accumulation in pepper hypocotyls. RNA-seq data showed that many genes related to anthocyanin biosynthesis and transport decreased significantly in the mutant. Yeast one-hybrid (Y1H) assays showed that CaHY5 can bind to the promoter of CaF3H, CaF3'5'H, CaDFR, CaANS and CaGST, which are important genes in anthocyanin biosynthesis or transport. Our results indicate that CaHY5 directly regulates anthocyanin biosynthesis and transport, thus governing anthocyanin accumulation in pepper hypocotyl. The mutant and gene identified in this work shall be valuable in the purity control of hybrid pepper seeds.

Transcriptional regulation of fleshy fruit texture

Fleshy fruit texture is a critically important quality characteristic of ripe fruit. Softening is an irreversible process which operates in most fleshy fruits during ripening which, together with changes in color and taste, contributes to improvements in mouthfeel and general attractiveness. Softening results mainly from the expression of genes encoding enzymes responsible for cell wall modifications but starch degradation and high levels of flavonoids can also contribute to texture change. Some fleshy fruit undergo lignification during development and post-harvest, which negatively affects eating quality. Excessive softening can also lead to physical damage and infection, particularly during transport and storage which causes severe supply chain losses. Many transcription factors (TFs) that regulate fruit texture by controlling the expression of genes involved in cell wall and starch metabolism have been characterized. Some TFs directly regulate cell wall targets, while others act as part of a broader regulatory program governing several aspects of the ripening process. In this review, we focus on advances in our understanding of the transcriptional regulatory mechanisms governing fruit textural change during fruit development, ripening and post-harvest. Potential targets for breeding and future research directions for the control of texture and quality improvement are discussed.

Contrasting Roles of Ethylene Response Factors in Pathogen Response and Ripening in Fleshy Fruit

Fleshy fruits are generally hard and unpalatable when unripe; however, as they mature, their quality is transformed by the complex and dynamic genetic and biochemical process of ripening, which affects all cell compartments. Ripening fruits are enriched with nutrients such as acids, sugars, vitamins, attractive volatiles and pigments and develop a pleasant taste and texture and become attractive to eat. Ripening also increases sensitivity to pathogens, and this presents a crucial problem for fruit postharvest transport and storage: how to enhance pathogen resistance while maintaining ripening quality. Fruit development and ripening involve many changes in gene expression regulated by transcription factors (TFs), some of which respond to hormones such as auxin, abscisic acid (ABA) and ethylene. Ethylene response factor (ERF) TFs regulate both fruit ripening and resistance to pathogen stresses. Different ERFs regulate fruit ripening and/or pathogen responses in both fleshy climacteric and non-climacteric fruits and function cooperatively or independently of other TFs. In this review, we summarize the current status of studies on ERFs that regulate fruit ripening and responses to infection by several fungal pathogens, including a systematic ERF transcriptome analysis of fungal grey mould infection of tomato caused by Botrytis cinerea. This deepening understanding of the function of ERFs in fruit ripening and pathogen responses may identify novel approaches for engineering transcriptional regulation to improve fruit quality and pathogen resistance.

Function deficiency of GhOMT1 causes anthocyanidins over-accumulation and diversifies fibre colours in cotton (Gossypium hirsutum)

Naturally coloured cotton (NCC) fibres need little or no dyeing process in textile industry to low-carbon emission and are environment-friendly. Proanthocyanidins (PAs) and their derivatives were considered as the main components causing fibre coloration and made NCCs very popular and healthy, but the monotonous fibre colours greatly limit the wide application of NCCs. Here a G. hirsutum empurpled mutant (HS2) caused by T-DNA insertion is found to enhance the anthocyanidins biosynthesis and accumulate anthocyanidins in the whole plant. HPLC and LC/MS-ESI analysis confirmed the anthocyanidins methylation and peonidin, petunidin and malvidin formation are blocked. The deficiency of GhOMT1 in HS2 was associated with the activation of the anthocyanidin biosynthesis and the altered components of anthocyanidins. The transcripts of key genes in anthocyanidin biosynthesis pathway are significantly up-regulated in HS2, while transcripts of the genes for transport and decoration were at similar levels as in WT. To investigate the potential mechanism of GhOMT1 deficiency in cotton fibre coloration, HS2 mutant was crossed with NCCs. Surprisingly, offsprings of HS2 and NCCs enhanced PAs biosynthesis and increased PAs levels in their fibres from the accumulated anthocyanidins through up-regulated GhANR and GhLAR. As expected, multiple novel lines with improved fibre colours including orange red and navy blue were produced in their generations. Based on this work, a new strategy for breeding diversified NCCs was brought out by promoting PA biosynthesis. This work will help shed light on mechanisms of PA biosynthesis and bring out potential molecular breeding strategy to increase PA levels in NCCs.

Ethylene Inhibits Anthocyanin Biosynthesis by Repressing the R2R3-MYB Regulator SlAN2-like in Tomato

Fruit ripening is usually accompanied by anthocyanin accumulation. Ethylene is key in ripening-induced anthocyanin production in many fruits. However, the effects of fruit ripening and ethylene on anthocyanin biosynthesis in purple tomato fruits are unclear. This study shows that bagged fruits of the purple tomato cultivar ‘Indigo Rose’ failed to produce anthocyanins at the red ripening stage after bag removal. In contrast, the bagged immature fruits accumulated a significant amount of anthocyanins after removing the bags. The transcriptomic analyses between immature and red ripening fruit before and after bag removal revealed that anthocyanin-related genes, including the key positive R2R3-MYB regulator SlAN2-like, were repressed in the red ripening fruit. The 86 identified transcription factors, including 13 AP2/ERF, 7 bZIP, 8 bHLH and 6 MYB, showed significantly different expressions between immature and red ripening fruits. Moreover, subjecting bagged immature fruits to exogenous ethylene treatment significantly inhibited anthocyanin accumulation and the expression of anthocyanin-related genes, including the anthocyanin structure genes and SlAN2-like. Thus, ethylene inhibits anthocyanin biosynthesis by repressing the transcription of SlAN2-like and other anthocyanin-related genes. These findings provide new insights into anthocyanin regulation in purple tomato fruit.

High CO2 Reduces Spoilage Caused by Botrytis cinerea in Strawberry Without Impairing Fruit Quality

High CO₂ (> 20 kPa) conditions are beneficial for suppressing spoilage caused by Botrytis cinerea in strawberry fruit; however, these conditions are often accompanied by discoloration, off-flavors, and faster softening. Stepwise increments of CO₂ concentrations have been proposed to alleviate injuries in fruits caused by high CO₂. In this study, we investigated whether stepwise increments of CO₂, up to 30 kPa and under a reduced O₂ concentration, are beneficial for reducing fungal spoilage without inducing CO₂ injury symptoms in strawberry fruit. Based on recommended settings (5-10 kPa O₂ with 15-20 kPa CO₂), we first selected optimal O₂ and CO₂ concentrations that best-reduced spoilage caused by B. cinerea in red ripe "Sonsation" strawberry fruit. We found that higher O₂ (10 kPa) and CO₂ (20 kPa) concentrations were most beneficial for prolonging strawberry fruit shelf life. Subsequently, we studied the performance of red ripe "Arabella" strawberry fruit stored at 5°C under different controlled atmosphere (CA) conditions (10 kPa O₂ with either 0, 20, or 30 kPa CO₂). The CO₂ concentrations were achieved either within 8 h or in a stepwise manner within the first 4 days of storage. As a control, 21 kPa O₂ and 0 kPa CO₂ were used. Following storage for up to 11 days, the spoilage incidence was assessed at 12°C for 5 days. The application of high CO₂ (20 and 30 kPa) combined with 10 kPa O₂ greatly suppressed fruit spoilage during storage and subsequent shelf life. High CO₂ suppressed respiration as well as maintained a higher pH and firmness in treated fruit. The level of total sugars did not change, but during storage, a substantial part of sucrose was converted into glucose and fructose, especially under high CO₂ conditions. High CO₂ did not affect ascorbic acid and anthocyanin levels. The stepwise increments of CO₂ did not result in beneficial effects compared to the static application of high CO₂. Our results show that "Arabella" strawberry fruit are highly tolerant to elevated CO₂ and can be stored under 30 kPa CO₂ to prolong the shelf life.

Integrated LC-MS/MS and Transcriptome Sequencing Analysis Reveals the Mechanism of Color Formation During Prickly Ash Fruit Ripening

Prickly ash peel is one of the eight major condiments in China and is widely used in cooking because of its unique fragrance and numbing taste. The color of prickly ash fruit is the most intuitive quality that affects consumer choice. However, the main components and key biosynthetic genes responsible for prickly ash fruit color have not yet been determined. To better understand the biosynthetic mechanisms and accumulation of prickly ash fruit color components, we performed an integrated transcriptomic and metabolomic analysis of red and green prickly ash fruit at different growth periods. The transcriptome analysis identified 17,269 differentially expressed genes (DEGs) between fruit of red and green prickly ash: 7,236 upregulated in green fruit and 10,033 downregulated. Liquid chromatography tandem mass spectrometry (LC-MS/MS) identified 214 flavonoids of 10 types. Flavonoids and flavonols are the main flavonoids in prickly ash, and the total flavonoid content of red prickly ash is higher than that of green prickly ash. Comprehensive analysis showed that the main colored metabolites that differed between green and red prickly ash were cyanidin-3-O-galactoside and cyanidin-3-O-glucoside, and differences in the contents of these metabolites were due mainly to differences in the expression of ANS and UFGT. Our results provide insight into the mechanisms underlying color differences in red and green prickly ash and will be useful for improving the quality of prickly ash fruit.

Genetic Manipulation and Bioreactor Culture of Plants as a Tool for Industry and Its Applications

In recent years, there has been a considerable increase in interest in the use of transgenic plants as sources of valuable secondary metabolites or recombinant proteins. This has been facilitated by the advent of genetic engineering technology with the possibility for direct modification of the expression of genes related to the biosynthesis of biologically active compounds. A wide range of research projects have yielded a number of efficient plant systems that produce specific secondary metabolites or recombinant proteins. Furthermore, the use of bioreactors allows production to be increased to industrial scales, which can quickly and cheaply deliver large amounts of material in a short time. The resulting plant production systems can function as small factories, and many of them that are targeted at a specific operation have been patented. This review paper summarizes the key research in the last ten years regarding the use of transgenic plants as small, green biofactories for the bioreactor-based production of secondary metabolites and recombinant proteins; it simultaneously examines the production of metabolites and recombinant proteins on an industrial scale and presents the current state of available patents in the field.

Volatile Metabolism of Wine Grape Trincadeira: Impact of Infection with Botrytis cinerea

The aroma of grapes is cultivar dependent and is influenced by terroir, vineyard practices, and abiotic and biotic stresses. Trincadeira is a non-aromatic variety associated with low phenolic content and high sugar and organic acid levels. This cultivar, widely used in Portuguese wines, presents high susceptibility to Botrytis cinerea. This work aimed to characterise the volatile profile of Trincadeira grapes and how it changes under infection with B. cinerea. Thirty-six volatile organic compounds were identified, from different functional groups, namely alcohols, ester acetates, fatty acid esters, fatty acids, aldehydes, and products of the lipoxygenase pathway. Both free and glycosidic volatile organic compounds were analysed by Gas Chromatography and Gas Chromatography coupled to Mass Spectrometry for component quantification and identification, respectively. A multivariance analysis showed a clear discrimination between healthy and infected grapes with 2-trans-hexenal and isoamyl-acetate among the compounds identified as negative and positive markers of infection, respectively. Ester acetates such as 2-phenylethyl acetate, isoamyl acetate, and 2-methylbutyl acetate were present in higher contents in infected samples, whereas the contents of several fatty acid esters, such as ethyl decanoate and ethyl dodecanoate, decreased. These data were integrated with quantitative PCR data regarding genes involved in volatile metabolism and showed up-regulation of a gene coding for Hydroperoxide Lyase 2 in infected grapes. Altogether, these changes in volatile metabolism indicate an impact on the grape quality and may be related to defence against B. cinerea. The presence/absence of specific compounds might be used as infection biomarkers in the assessment of Trincadeira grapes' quality.

Genomic prediction of strawberry resistance to postharvest fruit decay caused by the fungal pathogen Botrytis cinerea

Gray mold, a disease of strawberry (Fragaria × ananassa) caused by the ubiquitous necrotroph Botrytis cinerea, renders fruit unmarketable and causes economic losses in the postharvest supply chain. To explore the feasibility of selecting for increased resistance to gray mold, we undertook genetic and genomic prediction studies in strawberry populations segregating for fruit quality and shelf life traits hypothesized to pleiotropically affect susceptibility. As predicted, resistance to gray mold was heritable but quantitative and genetically complex. While every individual was susceptible, the speed of symptom progression and severity differed. Narrow-sense heritability ranged from 0.38 to 0.71 for lesion diameter (LD) and 0.39 to 0.44 for speed of emergence of external mycelium (EM). Even though significant additive genetic variation was observed for LD and EM, the phenotypic ranges were comparatively narrow and genome-wide analyses did not identify any large-effect loci. Genomic selection (GS) accuracy ranged from 0.28 to 0.59 for LD and 0.37 to 0.47 for EM. Additive genetic correlations between fruit quality and gray mold resistance traits were consistent with prevailing hypotheses: LD decreased as titratable acidity increased, whereas EM increased as soluble solid content decreased and firmness increased. We concluded that phenotypic and GS could be effective for reducing LD and increasing EM, especially in long shelf life populations, but that a significant fraction of the genetic variation for resistance to gray mold was caused by the pleiotropic effects of fruit quality traits that differ among market and shelf life classes.

Effect of Elevated Temperature on Tomato Post-Harvest Properties

The fleshy fruit of tomato (Solanum lycopersicum) is a commodity used worldwide as a fresh or processed product. Like many crops, tomato plants and harvested fruits are susceptible to the onset of climate change. Temperature plays a key role in tomato fruit production and ripening, including softening, development of fruit colour, flavour and aroma. The combination of climate change and the drive to reduce carbon emission and energy consumption is likely to affect tomato post-harvest storage conditions. In this study, we investigated the effect of an elevated storage temperature on tomato shelf life and fungal susceptibility. A collection of 41 genotypes with low and high field performance at elevated temperature, including different growth, fruit and market types, was used to assess post-harvest performances. A temperature increase from 18–20 °C to 26 °C reduced average shelf life of fruit by 4 days ± 1 day and increased fungal susceptibility by 11% ± 5% across all genotypes. We identified tomato varieties that exhibit both favourable post-harvest fruit quality and high field performance at elevated temperature. This work contributes to efforts to enhance crop resilience by selecting for thermotolerance combined with traits suitable to maintain and improve fruit quality, shelf life and pathogen susceptibility under changing climate conditions.

Calcium Positively Mediates Blue Light-Induced Anthocyanin Accumulation in Hypocotyl of Soybean Sprouts

Soybean sprouts are a flavorful microgreen that can be eaten all year round and are widely favored in Southeast Asia. In this study, the regulatory mechanism of calcium on anthocyanin biosynthesis in soybean sprouts under blue light was investigated. The results showed that blue light, with a short wavelength, effectively induced anthocyanin accumulation in the hypocotyl of soybean sprout cultivar "Dongnong 690." Calcium supplementation further enhanced anthocyanin content, which was obviously inhibited by LaCl₃ and neomycin treatment. Moreover, exogenous calcium changed the metabolism of anthocyanins, and seven anthocyanin compounds were detected. The trend of calcium fluorescence intensity in hypocotyl cells, as well as that of the inositol 1,4,5-trisphosphate and calmodulin content, was consistent with that of anthocyanins content. Specific spatial distribution patterns of calcium antimonate precipitation were observed in the ultrastructure of hypocotyl cells under different conditions. Furthermore, calcium application upregulated the expression of genes related to anthocyanin biosynthesis, and calcium inhibitors suppressed these genes. Finally, transcriptomics was performed to gain global insights into the molecular regulation mechanism of calcium-associated anthocyanin production. Genes from the flavonoid biosynthesis pathway were distinctly enriched among the differentially expressed genes, and weighted gene co-expression network analysis showed that two MYBs were related to the accumulation of anthocyanins. These results indicated that calcium released from apoplast and intracellular stores in specific spatial-temporal features promote blue light-induced anthocyanin accumulation by upregulation of the expression of genes related to anthocyanin synthesis of "Dongnong 690" hypocotyl. The findings deepen the understanding of the calcium regulation mechanism of blue light-induced anthocyanin accumulation in soybean sprouts, which will help growers produce high-quality foods beneficial for human health.

Multifaceted roles of nitric oxide in tomato fruit ripening: NO-induced metabolic rewiring and consequences for fruit quality traits

Nitric oxide (NO) has been implicated as part of the ripening regulatory network in fleshy fruits. However, very little is known about the simultaneous action of NO on the network of regulatory events and metabolic reactions behind ripening-related changes in fruit color, taste, aroma and nutritional value. Here, we performed an in-depth characterization of the concomitant changes in tomato (Solanum lycopersicum) fruit transcriptome and metabolome associated with the delayed-ripening phenotype caused by NO supplementation at the pre-climacteric stage. Approximately one-third of the fruit transcriptome was altered in response to NO, including a multilevel down-regulation of ripening regulatory genes, which in turn restricted the production and tissue sensitivity to ethylene. NO also repressed hydrogen peroxide-scavenging enzymes, intensifying nitro-oxidative stress and S-nitrosation and nitration events throughout ripening. Carotenoid, tocopherol, flavonoid and ascorbate biosynthesis were differentially affected by NO, resulting in overaccumulation of ascorbate (25%) and flavonoids (60%), and impaired lycopene production. In contrast, the biosynthesis of compounds related to tomato taste (sugars, organic acids, amino acids) and aroma (volatiles) was slightly affected by NO. Our findings indicate that NO triggers extensive transcriptional and metabolic rewiring at the early ripening stage, modifying tomato antioxidant composition with minimal impact on fruit taste and aroma.

Can gene editing reduce postharvest waste and loss of fruit, vegetables, and ornamentals?

Postharvest waste and loss of horticultural crops exacerbates the agricultural problems facing humankind and will continue to do so in the next decade. Fruits and vegetables provide us with a vast spectrum of healthful nutrients, and along with ornamentals, enrich our lives with a wide array of pleasant sensory experiences. These commodities are, however, highly perishable. Approximately 33% of the produce that is harvested is never consumed since these products naturally have a short shelf-life, which leads to postharvest loss and waste. This loss, however, could be reduced by breeding new crops that retain desirable traits and accrue less damage over the course of long supply chains. New gene-editing tools promise the rapid and inexpensive production of new varieties of crops with enhanced traits more easily than was previously possible. Our aim in this review is to critically evaluate gene editing as a tool to modify the biological pathways that determine fruit, vegetable, and ornamental quality, especially after storage. We provide brief and accessible overviews of both the CRISPR-Cas9 method and the produce supply chain. Next, we survey the literature of the last 30 years, to catalog genes that control or regulate quality or senescence traits that are "ripe" for gene editing. Finally, we discuss barriers to implementing gene editing for postharvest, from the limitations of experimental methods to international policy. We conclude that in spite of the hurdles that remain, gene editing of produce and ornamentals will likely have a measurable impact on reducing postharvest loss and waste in the next 5-10 years.

Metabolic engineering of tomato fruit enriched in L-DOPA

L-DOPA, also known as Levodopa or L-3,4-dihydroxyphenylalanine, is a non-standard amino acid, and the gold standard drug for the treatment for Parkinson's Disease (PD). Recently, a gene encoding the enzyme that is responsible for its synthesis, as a precursor of the coloured pigment group betalains, was identified in beetroot, BvCYP76AD6. We have engineered tomato fruit enriched in L-DOPA through overexpression of BvCYP76AD6 in a fruit specific manner. Analysis of the transgenic fruit revealed the feasibility of accumulating L-DOPA in a non-naturally betalain-producing plant. Fruit accumulating L-DOPA also showed major effects on the fruit metabolome. Some of these changes included elevation of amino acids levels, changes in the levels of intermediates of the TCA and glycolysis pathways and reductions in the levels of phenolic compounds and nitrogen-containing specialised metabolites. Furthermore, we were able to increase the L-DOPA levels further by elevating the expression of the metabolic master regulator, MYB12, specifically in tomato fruit, together with BvCYP76AD6. Our study elucidated new roles for L-DOPA in plants, because it impacted fruit quality parameters including antioxidant capacity and firmness. The L-DOPA levels achieved in tomato fruit were comparable to the levels in other non-seed organs of L-DOPA - accumulating plants, offering an opportunity to develop new biological sources of L-DOPA by widening the repertoire of L-DOPA-accumulating plants. These tomato fruit could be used as an alternative source of this important pharmaceutical.

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Tomato fruit were engineered to synthesise and accumulate L-DOPA.

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Co-expression of the transcription factor, MYB12, doubled the levels of L-DOPA in tomato fruit.

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The accumulation of L-DOPA resulted in additional changes in the profile of primary and secondary metabolites in tomatoes.

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The L-DOPA tomato fruit exhibited improved shelf life and reduced susceptibility to Botrytis cinerea.

Anthocyanin Accumulation and Transcriptional Regulation of Anthocyanin Biosynthesis in Purple Pepper

Pepper (Capsicum annuum) is among the important horticultural crops with economic value, and more and more colorful varieties have been marketed. The purple pepper is becoming increasingly popular on the consumer market because of its anthocyanin richness. Here, two cyanidin-based anthocyanins were separated and identified from peels of purple cultivars by HPLC-LC-MS. To study the molecular mechanism of anthocyanin accumulation, the differential expression of genes related to anthocyanin biosynthesis was examined by qRT-PCR and RNA-Seq in peel from green and purple cultivars. These results show that CaANT1, CaANT2, CaAN1, and CaTTG1 are involved in anthocyanin accumulation of pepper. Further investigation suggested that CaANT1, CaANT2, CaAN1, and CaTTG1 can activate anthocyanin accumulation via forming a new MMBW transcription complex.

Phenotypic Variation of Botrytis cinerea Isolates Is Influenced by Spectral Light Quality

Botrytis cinerea, a fungal pathogen that causes gray mold, displays a high degree of phenotypic diversity. Light emitting diodes (LEDs) with specific light spectrum are increasingly used as lighting resource for plant greenhouse production. The chosen light spectrum can also have an effect on the pathogens in this production system. In this study, we investigated the phenological diversity in 15 B. cinerea isolates upon different light treatments. Daylight, darkness, and LED lights with different wavelengths (white, blue, red, blue+red) were chosen as treatments. The 15 Botrytis isolates differed in their mycelial growth rate, conidia production, and sclerotia formation. Light quality had a limited effect on growth rate. All isolates sporulated under daylight treatment, red light resulted in lower sporulation, while white, blue, and blue+red light inhibited sclerotia formation in all isolates, and sporulation in most, but not all isolates. Pathogenicity of the Botrytis isolates was studied on 2-week-old strawberry (Fragaria × ananassa 'Elsanta') leaves grown under white, blue, and red LED lights. The isolates differed in virulence on strawberry leaves, and this was positively correlated to oxalic acid production by B. cinerea in vitro. Red LED light improved leaf basal resistance to all the tested Botrytis isolates. Blue light pretreatment resulted in decreased leaf resistance to some isolates. Furthermore, we used image analysis to quantify the virulence of the different Botrytis isolates based on changes in photosynthetic performance of the strawberry leaves: chlorophyll fluorescence (Fv/Fm), chlorophyll index (ChlIdx) and anthocyanin content (modified anthocyanin reflection index, mAriIdx). Fv/Fm showed a strong negative correlation with disease severity and can be an indicator for the early detection of gray mold on strawberry leaves.

Comparative transcriptome analysis of differentially expressed genes between the fruit peel and flesh of the purple tomato cultivar 'Indigo Rose'

Anthocyanins are considered health-promoting phytonutrients; however, anthocyanins strictly occurr in the fruit peel of purple tomato cultivars, making the total anthocyanin content limited per tomato fruit. In this study, we performed a transcriptome analysis between the fruit peel and flesh of a purple tomato cultivar 'Indigo Rose' at both the mature green stage and breaking stage. In total, 1,945 differently expressed genes, including 165 transcription factors, were detected between the fruit peel and flesh, both at and after the mature green stage. We further analyzed the transcription of anthocyanin biosynthesis genes and the regulatory genes composing the MYB-bHLH-WD40 (MBW) complex between the fruit peel and flesh at both development stages. In addition, several light-sensing genes and other transcription factor genes, including BBX family genes and WRKY genes, showed different expression patterns between the fruit peel and flesh. These findings deepen our understanding of anthocyanin biosynthesis in tomato fruit peels and facilitate the identification of genes limiting the anthocyanin biosynthesis in tomato fruit flesh.

Impact of Paraburkholderia phytofirmans PsJN on Grapevine Phenolic Metabolism

Phenolic compounds are implied in plant-microorganisms interaction and may be induced in response to plant growth-promoting rhizobacteria (PGPRs). Among PGPR, the beneficial bacterium Paraburkholderia phytofirmans PsJN was previously described to stimulate the growth of plants and to induce a better adaptation to both abiotic and biotic stresses. This study aimed to investigate the impact of PsJN on grapevine secondary metabolism. For this purpose, gene expression (qRT-PCR) and profiling of plant secondary metabolites (UHPLC-UV/DAD-MS QTOF) from both grapevine root and leaves were compared between non-bacterized and PsJN-bacterized grapevine plantlets. Our results showed that PsJN induced locally (roots) and systemically (leaves) an overexpression of PAL and STS and specifically in leaves the overexpression of all the genes implied in phenylpropanoid and flavonoid pathways. Moreover, the metabolomic approach revealed that relative amounts of 32 and 17 compounds in roots and leaves, respectively, were significantly modified by PsJN. Once identified to be accumulated in response to PsJN by the metabolomic approach, antifungal properties of purified molecules were validated in vitro for their antifungal effect on Botrytis cinerea spore germination. Taking together, our findings on the impact of PsJN on phenolic metabolism allowed us to identify a supplementary biocontrol mechanism developed by this PGPR to induce plant resistance against pathogens.

Nutraceutical Characterization of Anthocyanin-Rich Fruits Produced by "Sun Black" Tomato Line

Tomato (Solanum lycopersicum L.) is one of the most cultivated vegetable in the world and it represents a large source of bioactive compounds, including carotenoids and polyphenols (phenolic acids and flavonoids). However, the concentration of flavonoids in tomato is considered sub-optimal, particularly because anthocyanins are not generally present. Therefore, this crop has been the object of an intense metabolic engineering in order to obtain anthocyanin-enriched tomatoes by using either breeding or transgenic strategies. Some wild tomato species, such as S. chilense and S. cheesmaniae, biosynthesize anthocyanins in the fruit sub-epidermal tissue, and some alleles from those genotypes have been introgressed into a new developed purple tomato line, called “Sun Black” (SB). It is a tomato line with a purple skin color, both in green and in red fruit stages, due to the biosynthesis of anthocyanins in the peel, and a normal red color pulp, with a taste just like a traditional tomato. SB is the result of a breeding programme and it is not a genetically modified (GM) product. We report the chemical characterization and structure elucidation of the attractive anthocyanins found in the peel of SB tomato, as well as other bioactive compounds (carotenoids, polyphenols, vitamin C) of the whole fruit. Using one- and two-dimensional NMR experiments, the two main anthocyanins were identified to be petunidin 3-O-[6″-O-(4^‴-O-E-p-coumaroyl-α-rhamnopyranosyl) -β-glucopyranoside]-5-O-β-glucopyranoside (petanin) and malvidin 3-O-[6″-O-(4^‴-O-E-p-coumaroyl-α-rhamnopyranosyl)-β-glucopyranoside]-5-O-β-glucopyranoside (negretein). The total anthocyanins in the whole ripe fruit was 1.2 mg/g dry weight (DW); 7.1 mg/100 g fresh weight (FW). Chlorogenic acid (the most abundant phenolic acid) was 0.6 mg/g DW; 3.7 mg/100 g FW. The main flavonol, rutin was 0.8 mg/g DW; 5 mg/100 g FW. The total carotenoid content was 211.3 μg/g DW; 1,268 μg/100 g FW. The total phenolic content was 8.6 mg/g DW; 52.2 mg/100 g FW. The vitamin C content was 37.3 mg/100 g FW. The antioxidant activities as measured by the TEAC and ORAC assays were 31.6 and 140.3 μmol TE/g DW, respectively (193 and 855.8 μmol TE/100 g FW, respectively). The results show the unique features of this new tomato genotype with nutraceutical properties.

Identification of miRNAs involved in fruit ripening by deep sequencing of Olea europaea L. transcriptome

BACKGROUND

The ripening process of olive fruits is associated with chemical and/or enzymatic specific transformations, making them particularly attractive to animals and humans. In olive drupes, including 'Cassanese' ones, ripening is usually accompanied by progressive chromatic change, resulting in a final red-brown colourization of both epidermis and mesocarp. This event has an exception in the 'Leucocarpa', in which we observed the destabilization in the equilibrium between the chlorophyll metabolism and that of the other pigments, particularly the anthocyanins, whose switch-off during maturation promotes the white colouration of the fruits. Recently, transcription profiling of 'Leucocarpa' and 'Cassanese' olives along ripening, performed through an Illumina RNA-seq approach, has provided useful insights on genes functions involved in fruit maturation such as those related to the biosynthesis of flavonoids and anthocyanins.

METHODOLOGY

To assess expression alterations of genes involved in flavonoids and anthocyanins biosynthetic pathways during ripening, possibly caused by small nuclear RNA (snRNA) in olive drupes, snRNA libraries from 'Leucocarpa' and 'Cassanese' were constructed with RNAs extracted at 100 and 130 Days After Flowering (DAF) and sequenced by an Illumina approach. 130 conserved microRNAs (miRNA) in the Viridiplantae belonging to 14 miRNA families were identified. Regarding the 130 conserved miRNAs, approximately the 48% were identified in all libraries, 5 and 18 miRNAs were shared between the "Cassanese" (C100, C130) and "Leucocarpa" (L100, L130) libraries, respectively.

CONCLUSION

For the remaining reads not-matching with known miRNAs in the Viridiplantae, we combined secondary structure and minimum free energy to discover novel olive miRNAs. Based on these analyses, 492 sequences were considered as putative novel miRNAs. The putative target genes of identified miRNA were computationally predicted by alignment with the olive drupe transcripts obtained from the same samples. A total of 218 transcripts were predicted as targets of 130 known and 492 putative novel miRNAs. Interestingly, some identified target genes are involved in negative regulation of anthocyanin metabolic process. Quantification of the expression pattern of three miRNA and their target transcripts by qRT-PCR assay confirmed the results of Illumina sequencing.

Grey mould of strawberry, a devastating disease caused by the ubiquitous necrotrophic fungal pathogen Botrytis cinerea

The fungal pathogen Botrytis cinerea causes grey mould, a commercially damaging disease of strawberry. This pathogen affects fruit in the field, storage, transport and market. The presence of grey mould is the most common reason for fruit rejection by growers, shippers and consumers, leading to significant economic losses. Here, we review the biology and epidemiology of the pathogen, mechanisms of infection and the genetics of host plant resistance. The development of grey mould is affected by environmental and genetic factors; however, little is known about how B. cinerea and strawberry interact at the molecular level. Despite intensive efforts, breeding strawberry for resistance to grey mould has not been successful, and the mechanisms underlying tolerance to B. cinerea are poorly understood and under-investigated. Current control strategies against grey mould include pre- and postharvest fungicides, yet they are generally ineffective and expensive. In this review, we examine available research on horticultural management, chemical and biological control of the pathogen in the field and postharvest storage, and discuss their relevance for integrative disease management. Additionally, we identify and propose approaches for increasing resistance to B. cinerea in strawberry by tapping into natural genetic variation and manipulating host factors via genetic engineering and genome editing.

Looking at Flavonoid Biodiversity in Horticultural Crops: A Colored Mine with Nutritional Benefits

Flavonoids represent a wide group of plant secondary metabolites implicated in many physiological roles, from the attraction of pollinators to the protection against biotic or abiotic stresses. Flavonoids are synthetized in a number of horticultural crops that are important components of our daily diet. In the last decades, the consumption of vegetables rich in antioxidants has been strongly promoted from the perspective of prevention/protection against chronic diseases. Therefore, due to their nutritional importance, several attempts have been made to enhance flavonoid levels in species of agronomic interest. In this review, we focus on the flavonoid biodiversity among the major horticultural species, which is responsible of differences among closely related species and influences the qualitative/quantitative composition. We also review the role of flavonoids in the nutritional quality of plant products, contributing to their organoleptic and nutritional properties, and the main strategies of biofortification to increase their content.

Optimizing shelf life conditions for anthocyanin-rich tomatoes

Shelf life is the time a product can be stored without losing its qualitative characteristics. It represents one of the most critical quality traits for food products, particularly for fleshy fruits, including tomatoes. Tomatoes' shelf life is usually shortened due to fast over-ripening caused by several different factors, among which changes in temperature, respiration and pathogen exposure. Although tomatoes usually do not contain anthocyanins, varieties enriched in these antioxidant compounds have been recently developed. The anthocyanin-rich tomatoes have been shown to possess a significantly extended shelf life by delayed over-ripening and reduction of the susceptibility to certain pathogens. In the present work, we compared different conditions of postharvest storage of anthocyanin-rich tomato fruits with the aim to understand if the added value represented by the presence of the anthocyanins in the fruit peel can be affected in postharvest. For this purpose we used an anthocyanin-enriched tomato line derived from conventional breeding and took into consideration different light and temperature conditions, known to affect fruit physiology during postharvest as well as anthocyanin production. Several quality traits related to the fruit ripening were measured, including anthocyanin and carotenoid content, pH, titratable acidity and total soluble solids. In this way we identified that the most suitable fruit storage and postharvest anthocyanin accumulation were obtained through exposure to cool temperature (12° C), particularly in the presence of light. Under these parameters, tomato fruits showed increased anthocyanin content and unchanged flavour-related features up to three weeks after harvesting.

Anthocyanin Biosynthesis and Degradation Mechanisms in Solanaceous Vegetables: A Review

Anthocyanins are a group of polyphenolic pigments that are ubiquitously found in the plant kingdom. In plants, anthocyanins play a role not only in reproduction, by attracting pollinators and seed dispersers, but also in protection against various abiotic and biotic stresses. There is accumulating evidence that anthocyanins have health-promoting properties, which makes anthocyanin metabolism an interesting target for breeders and researchers. In this review, the state of the art knowledge concerning anthocyanins in the Solanaceous vegetables, i.e., pepper, tomato, eggplant, and potato, is discussed, including biochemistry and biological function of anthocyanins, as well as their genetic and environmental regulation. Anthocyanin accumulation is determined by the balance between biosynthesis and degradation. Although the anthocyanin biosynthetic pathway has been well-studied in Solanaceous vegetables, more research is needed on the inhibition of biosynthesis and, in particular, the anthocyanin degradation mechanisms if we want to control anthocyanin content of Solanaceous vegetables. In addition, anthocyanin metabolism is distinctly affected by environmental conditions, but the molecular regulation of these effects is poorly understood. Existing knowledge is summarized and current gaps in our understanding are highlighted and discussed, to create opportunities for the development of anthocyanin-rich crops through breeding and environmental management.

A MYB transcription factor, DcMYB6, is involved in regulating anthocyanin biosynthesis in purple carrot taproots

Carrots are widely grown and enjoyed around the world. Purple carrots accumulate rich anthocyanins in the taproots, while orange, yellow, and red carrots accumulate rich carotenoids in the taproots. Our previous studies indicated that variation in the activity of regulatory genes may be responsible for variations in anthocyanin production among various carrot cultivars. In this study, an R2R3-type MYB gene, designated as DcMYB6, was isolated from a purple carrot cultivar. In a phylogenetic analysis, DcMYB6 was grouped into an anthocyanin biosynthesis-related MYB clade. Sequence analyses revealed that DcMYB6 contained the conserved bHLH-interaction motif and two atypical motifs of anthocyanin regulators. The expression pattern of DcMYB6 was correlated with anthocyanin production. DcMYB6 transcripts were detected at high levels in three purple carrot cultivars but at much lower levels in six non-purple carrot cultivars. Overexpression of DcMYB6 in Arabidopsis led to enhanced anthocyanin accumulation in both vegetative and reproductive tissues and upregulated transcript levels of all seven tested anthocyanin-related structural genes. Together, these results show that DcMYB6 is involved in regulating anthocyanin biosynthesis in purple carrots. Our results provide new insights into the regulation of anthocyanin synthesis in purple carrot cultivars.

A label-free differential proteomics analysis reveals the effect of melatonin on promoting fruit ripening and anthocyanin accumulation upon postharvest in tomato

To better understand the function of melatonin in tomato fruit ripening and quality improvement, a label-free quantitation method was used to investigate the proteins that differ between the control (CK) and 50 μm melatonin treatment (M50) fruits. Proteomics data identified 241 proteins that were significantly influenced by melatonin. These proteins were involved in several ripening-related pathways, including cell wall metabolism, oxidative phosphorylation, carbohydrate, and fatty acid metabolism. Moreover, the application of exogenous melatonin increased eight proteins that are related to anthocyanin accumulation during fruit ripening. Additionally, the affected protein levels correlated with the corresponding gene transcript levels. Further, the total anthocyanin content from M50 increased by 52%, 48%, and 50% at 5, 8, and 13 DAT (day after melatonin treatment), respectively. The melatonin-mediated promotion of fruit ripening and quality might be due to the altered proteins involved in processes associated with ripening. In this work, we indicated that a senescence-related protein was downregulated in the M50 fruit, while a cell apoptosis inhibitor (API5) protein was upregulated. In addition, peroxidases (POD9, POD12, peroxidase p7-like) and catalase (CAT3) significantly increased in the M50 fruits. Based on the previous studies and our data, we inferred that melatonin might be positively related to fruit ripening but negatively related to fruit senescence. This research provides insights into the physiological and molecular mechanisms underlying melatonin-mediated fruit ripening as well as the anthocyanin formation process in tomato fruit at the protein concentration level, and we reveal possible candidates for regulation of anthocyanin formation during fruit ripening.

Comparative Leaves Transcriptome Analysis Emphasizing on Accumulation of Anthocyanins in Brassica: Molecular Regulation and Potential Interaction with Photosynthesis

The purple leaf pigmentation mainly associated with anthocyanins accumulation is common in Brassica but the mechanisms of its production and its potential physiological functions are poorly understood. Here, we performed the phenotypic, cytological, physiological, and comparative leaves transcriptome analyses of 11 different varieties belonging to five Brassica species with purple or green leaves. We observed that the anthocyanin was accumulated in most of vegetative tissues in all species and also in reproduction organs of B. carinata. Anthocyanin accumulated in different part of purple leaves including adaxial and abaxial epidermal cells as well as palisade and spongy mesophyll cells. Leave transcriptome analysis showed that almost all late biosynthetic genes (LBGs) of anthocyanin, especially Dihydroflavonol 4-Reductase (DFR), Anthocyanidin Synthase (ANS) and Transparent Testa 19 (TT19), were highly up-regulated in all purple leaves. However, only one of transcript factors in anthocyanin biosynthesis pathway, Transparent Testa 8 (TT8), was up regulated along with those genes in all purple leaves, indicating its pivotal role for anthocyanin production in Brassica. Interestingly, with the up-regulation of genes for anthocyanin synthesis, Cytosolic 6-phosphogluconolactonase (PLG5) which involved in the oxidative pentose-phosphate pathway was up-regulated in all purple leaves and three genes FTSH PROTEASE 8 (FTS8), GLYCOLATE OXIDASE 1 (GOX1), and GLUTAMINE SYNTHETASE 1;4 (GLN1;4) related to degradation of photo-damaged proteins in photosystem II and light respiration were down-regulated. These results highlighted the potential physiological functions of anthocyanin accumulation related to photosynthesis which might be of great worth in future.

The Tomato Hoffman's Anthocyaninless Gene Encodes a bHLH Transcription Factor Involved in Anthocyanin Biosynthesis That Is Developmentally Regulated and Induced by Low Temperatures

Anthocyanin pigments play many roles in plants, including providing protection against biotic and abiotic stresses. Many of the genes that mediate anthocyanin accumulation have been identified through studies of flowers and fruits; however, the mechanisms of genes involved in anthocyanin regulation in seedlings under low-temperature stimulus are less well understood. Genetic characterization of a tomato inbred line, FMTT271, which showed no anthocyanin pigmentation, revealed a mutation in a bHLH transcription factor (TF) gene, which corresponds to the ah (Hoffman's anthocyaninless) locus, and so the gene in FMTT271 at that locus was named ah. Overexpression of the wild type allele of AH in FMTT271 resulted in greater anthocyanin accumulation and increased expression of several genes in the anthocyanin biosynthetic pathway. The expression of AH and anthocyanin accumulation in seedlings was shown to be developmentally regulated and induced by low-temperature stress. Additionally, transcriptome analyses of hypocotyls and leaves from the near-isogenic lines seedlings revealed that AH not only influences the expression of anthocyanin biosynthetic genes, but also genes associated with responses to abiotic stress. Furthermore, the ah mutation was shown to cause accumulation of reactive oxidative species and the constitutive activation of defense responses under cold conditions. These results suggest that AH regulates anthocyanin biosynthesis, thereby playing a protective role, and that this function is particularly important in young seedlings that are particularly vulnerable to abiotic stresses.

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.

Induced mutations in tomato SlExp1 alter cell wall metabolism and delay fruit softening

Fruit ripening and softening are key traits for many fleshy fruit. Since cell walls play a key role in the softening process, expansins have been investigated to control fruit over ripening and deterioration. In tomato, expression of Expansin 1 gene, SlExp1, during fruit ripening was associated with fruit softening. To engineer tomato plants with long shelf life, we screened for mutant plants impaired in SlExp1 function. Characterization of two induced mutations, Slexp1-6_W211S, and Slexp1-7_Q213Stop, showed that SlExp1 loss of function leads to enhanced fruit firmness and delayed fruit ripening. Analysis of cell wall polysaccharide composition of Slexp1-7_Q213Stop mutant pointed out significant differences for uronic acid, neutral sugar and total sugar contents. Hemicelluloses chemistry analysis by endo-β-1,4-d-glucanase hydrolysis and MALDI-TOF spectrometry revealed that xyloglucan structures were affected in the fruit pericarp of Slexp1-7_Q213Stop mutant. Altogether, these results demonstrated that SlExp1 loss of function mutants yield firmer and late ripening fruits through modification of hemicellulose structure. These SlExp1 mutants represent good tools for breeding long shelf life tomato lines with contrasted fruit texture as well as for the understanding of the cell wall polysaccharide assembly dynamics in fleshy fruits.

Elucidating the genetic basis of antioxidant status in lettuce (Lactuca sativa)

A diet rich in phytonutrients from fruit and vegetables has been acknowledged to afford protection against a range of human diseases, but many of the most popular vegetables are low in phytonutrients. Wild relatives of crops may contain allelic variation for genes determining the concentrations of these beneficial phytonutrients, and therefore understanding the genetic basis of this variation is important for breeding efforts to enhance nutritional quality. In this study, lettuce recombinant inbred lines, generated from a cross between wild and cultivated lettuce (Lactuca serriola and Lactuca sativa, respectively), were analysed for antioxidant (AO) potential and important phytonutrients including carotenoids, chlorophyll and phenolic compounds. When grown in two environments, 96 quantitative trait loci (QTL) were identified for these nutritional traits: 4 for AO potential, 2 for carotenoid content, 3 for total chlorophyll content and 87 for individual phenolic compounds (two per compound on average). Most often, the L. serriola alleles conferred an increase in total AOs and metabolites. Candidate genes underlying these QTL were identified by BLASTn searches; in several cases, these had functions suggesting involvement in phytonutrient biosynthetic pathways. Analysis of a QTL on linkage group 3, which accounted for >30% of the variation in AO potential, revealed several candidate genes encoding multiple MYB transcription factors which regulate flavonoid biosynthesis and flavanone 3-hydroxylase, an enzyme involved in the biosynthesis of the flavonoids quercetin and kaempferol, which are known to have powerful AO activity. Follow-up quantitative RT-PCR of these candidates revealed that 5 out of 10 genes investigated were significantly differentially expressed between the wild and cultivated parents, providing further evidence of their potential involvement in determining the contrasting phenotypes. These results offer exciting opportunities to improve the nutritional content and health benefits of lettuce through marker-assisted breeding.

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

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

Application of Pseudomonas fluorescens to Blackberry under Field Conditions Improves Fruit Quality by Modifying Flavonoid Metabolism

Application of a plant growth promoting rhizobacterium (PGPR), Pseudomonas fluorescens N21.4, to roots of blackberries (Rubus sp.) is part of an optimised cultivation practice to improve yields and quality of fruit throughout the year in this important fruit crop. Blackberries are especially rich in flavonoids and therefore offer potential benefits for human health in prevention or amelioration of chronic diseases. However, the phenylpropanoid pathway and its regulation during ripening have not been studied in detail, in this species. PGPR may trigger flavonoid biosynthesis as part of an induced systemic response (ISR) given the important role of this pathway in plant defence, to cause increased levels of flavonoids in the fruit. We have identified structural genes encoding enzymes of the phenylpropanoid and flavonoid biosynthetic pathways catalysing the conversion of phenylalanine to the final products including flavonols, anthocyanins and catechins from blackberry, and regulatory genes likely involved in controlling the activity of pathway branches. We have also measured the major flavonols, anthocyanins and catechins at three stages during ripening. Our results demonstrate the coordinated expression of flavonoid biosynthetic genes with the accumulation of anthocyanins, catechins, and flavonols in developing fruits of blackberry. Elicitation of blackberry plants by treatment of roots with P.fluorescens N21.4, caused increased expression of some flavonoid biosynthetic genes and an accompanying increase in the concentration of selected flavonoids in fruits. Our data demonstrate the physiological mechanisms involved in the improvement of fruit quality by PGPR under field conditions, and highlight some of the genetic targets of elicitation by beneficial bacteria.

Mind the gap-deficits in our knowledge of aspects impacting the bioavailability of phytochemicals and their metabolites--a position paper focusing on carotenoids and polyphenols

Various secondary plant metabolites or phytochemicals, including polyphenols and carotenoids, have been associated with a variety of health benefits, such as reduced incidence of type 2 diabetes, cardiovascular diseases, and several types of cancer, most likely due to their involvement in ameliorating inflammation and oxidative stress. However, discrepancies exist between their putative effects when comparing observational and intervention studies, especially when using pure compounds. These discrepancies may in part be explained by differences in intake levels and their bioavailability. Prior to exerting their bioactivity, these compounds must be made bioavailable, and considerable differences may arise due to their matrix release, changes during digestion, uptake, metabolism, and biodistribution, even before considering dose- and host-related factors. Though many insights have been gained on factors affecting secondary plant metabolite bioavailability, many gaps still exist in our knowledge. In this position paper, we highlight several major gaps in our understanding of phytochemical bioavailability, including effects of food processing, changes during digestion, involvement of cellular transporters in influx/efflux through the gastrointestinal epithelium, changes during colonic fermentation, and their phase I and phase II metabolism following absorption.

Transcriptome and metabolome reprogramming in Vitis vinifera cv. Trincadeira berries upon infection with Botrytis cinerea

Vitis vinifera berries are sensitive towards infection by the necrotrophic pathogen Botrytis cinerea, leading to important economic losses worldwide. The combined analysis of the transcriptome and metabolome associated with fungal infection has not been performed previously in grapes or in another fleshy fruit. In an attempt to identify the molecular and metabolic mechanisms associated with the infection, peppercorn-sized fruits were infected in the field. Green and veraison berries were collected following infection for microarray analysis complemented with metabolic profiling of primary and other soluble metabolites and of volatile emissions. The results provided evidence of a reprogramming of carbohydrate and lipid metabolisms towards increased synthesis of secondary metabolites involved in plant defence, such as trans-resveratrol and gallic acid. This response was already activated in infected green berries with the putative involvement of jasmonic acid, ethylene, polyamines, and auxins, whereas salicylic acid did not seem to be involved. Genes encoding WRKY transcription factors, pathogenesis-related proteins, glutathione S-transferase, stilbene synthase, and phenylalanine ammonia-lyase were upregulated in infected berries. However, salicylic acid signalling was activated in healthy ripening berries along with the expression of proteins of the NBS-LRR superfamily and protein kinases, suggesting that the pathogen is able to shut down defences existing in healthy ripening berries. Furthermore, this study provided metabolic biomarkers of infection such as azelaic acid, a substance known to prime plant defence responses, arabitol, ribitol, 4-amino butanoic acid, 1-O-methyl- glucopyranoside, and several fatty acids that alone or in combination can be used to monitor Botrytis infection early in the vineyard.

In vitro regeneration of eight cultivars of Brassica oleracea var. capitata

Eight cultivars of Brassica oleracea var. capitata and two types of explant (hypocotyl and cotyledon) were tested for their potential to regenerate under in vitro conditions. Hypocotyl and cotyledon explants from 10-d-old seedlings were subcultured onto different callus induction media based on Murashige and Skoog (MS) basal medium supplemented with 1% sucrose and different concentrations and combinations of plant growth regulators. Hypocotyl explants were found to be more suitable for callus induction and organogenesis than cotyledon explants for all cultivars tested. In terms of regeneration, the cv. 'Amager' was significantly more responsive than the other cultivars tested and produced the highest number of shoots/buds per explant. Moreover, among five types of media tested, MS + 8.88 μM 6-benzyloaminopurine (BAP) + 0.53 μM α-naphthylacetic acid (NAA) was most effective for shoot regeneration. Rooting was achieved within 10-15 d on all the rooting media, but MS medium containing 5.37 μM NAA produced the maximum number of strong and healthy roots. Plantlets (95%) were subsequently established in the greenhouse, and no phenotypic variations were observed among regenerated plants. This plant regeneration protocol could be suitable for a wide range of cabbage cultivars.

Flavonoids: a metabolic network mediating plants adaptation to their real estate

From an evolutionary perspective, the emergence of the sophisticated chemical scaffolds of flavonoid molecules represents a key step in the colonization of Earth's terrestrial environment by vascular plants nearly 500 million years ago. The subsequent evolution of flavonoids through recruitment and modification of ancestors involved in primary metabolism has allowed vascular plants to cope with pathogen invasion and damaging UV light. The functional properties of flavonoids as a unique combination of different classes of compounds vary significantly depending on the demands of their local real estate. Apart from geographical location, the composition of flavonoids is largely dependent on the plant species, their developmental stage, tissue type, subcellular localization, and key ecological influences of both biotic and abiotic origin. Molecular and metabolic cross-talk between flavonoid and other pathways as a result of the re-direction of intermediate molecules have been well investigated. This metabolic plasticity is a key factor in plant adaptive strength and is of paramount importance for early land plants adaptation to their local ecosystems. In human and animal health the biological and pharmacological activities of flavonoids have been investigated in great depth and have shown a wide range of anti-inflammatory, anti-oxidant, anti-microbial, and anti-cancer properties. In this paper we review the application of advanced gene technologies for targeted reprogramming of the flavonoid pathway in plants to understand its molecular functions and explore opportunities for major improvements in forage plants enhancing animal health and production.

Reactive oxygen species produced via plasma membrane NADPH oxidase regulate anthocyanin synthesis in apple peel

Solar ultraviolet irradiation regulates anthocyanin synthesis in apple peel by modulating the production of reactive oxygen species via plasma membrane NADPH oxidase instead of other pathways. The synthesis of anthocyanin in apple peels is dependent upon solar irradiation. Using 3-mm commercial glass to attenuate solar UV-A and UV-B light, we confirmed that solar UV irradiation regulated anthocyanin synthesis in apple peels after exposing previously bagged fruit to sunlight. During sunlight exposure, UV attenuation did not affect the expression of MdHY5, MdCOP1, or MdCRY2, but significantly lowered plasma membrane NADPH oxidase activity and superoxide anion concentrations. UV attenuation also reduced the expression levels of MdMYB10, MdPAL, MdCHS, MdF3H, MdDFR, MdANS and MdUFGT1, UDP-glycose:flavonoid 3-O-glycosyltransferase (UFGT) activity, and local concentrations of anthocyanin and quercetin-3-glycoside. In contrast, exogenous application of hydrogen peroxide could enhance anthocyanin and quercetin-3-glycoside synthesis. Xanthophyll cycle pool size on a chlorophyll basis was higher but its de-epoxidation was lower under direct sunlight irradiation than that under UV-attenuating conditions. This suggests that reactive oxygen species (ROS) produced in chloroplast are not major contributors to anthocyanin synthesis regulation. Inhibition of plasma membrane NADPH oxidase activity lowered the production of ROS through this mechanism, significantly inhibited the synthesis of anthocyanin, and increased the total production of ROS in apple peel under direct sunlight irradiation, suggesting that ROS produced via plasma membrane NADPH oxidase regulates anthocyanin synthesis. In summary, solar UV irradiation regulated anthocyanin synthesis in apple peels by modulating the production of ROS via plasma membrane NADPH oxidase.