Phenylalanine treatment induces tomato resistance to Tuta absoluta via increased accumulation of benzenoid/phenylpropanoid volatiles serving as defense signals

Tuta absoluta ("leafminer"), is a major pest of tomato crops worldwide. Controlling this insect is difficult due to its efficient infestation, rapid proliferation, and resilience to changing weather conditions. Furthermore, chemical pesticides have only a short-term effect due to rapid development of T. absoluta strains. Here, we show that a variety of tomato cultivars, treated with external phenylalanine solutions exhibit high resistance to T. absoluta, under both greenhouse and open field conditions, at different locations. A large-scale metabolomic study revealed that tomato leaves absorb and metabolize externally given Phe efficiently, resulting in a change in their volatile profile, and repellence of T. absoluta moths. The change in the volatile profile is due to an increase in three phenylalanine-derived benzenoid phenylpropanoid volatiles (BPVs), benzaldehyde, phenylacetaldehyde, and 2-phenylethanol. This treatment had no effect on terpenes and green leaf volatiles, known to contribute to the fight against insects. Phe-treated plants also increased the resistance of neighboring non-treated plants. RNAseq analysis of the neighboring non-treated plants revealed an exclusive upregulation of genes, with enrichment of genes related to the plant immune response system. Exposure of tomato plants to either benzaldehyde, phenylacetaldehyde, or 2-phenylethanol, resulted in induction of genes related to the plant immune system that were also induced due to neighboring Phe-treated plants. We suggest a novel role of phenylalanine-derived BPVs as mediators of plant-insect interactions, acting as inducers of the plant defense mechanisms.

Phenylalanine in motion: A tale of an essential molecule with many faces

Phenylalanine has a unique role in plants as a source of a wide range of specialized metabolites, named phenylpropanoids that contribute to the adjustment of plants to changing developmental and environmental conditions. The profile of these metabolites differs between plants and plant organs. Some of the prominent phenylpropanoids include anthocyanins, phenolic acids, flavonoids, tannins, stilbenes, lignins, glucosinolates and benzenoid phenylpropanoid volatiles. Phenylalanine biosynthesis, leading to increased phenylpropanoid levels, is induced under stress. However, high availability of phenylalanine in plants under non-stressed conditions can be achieved either by genetically engineering plants to overproduce phenylalanine, or by external treatment of whole plants or detached plant organs with phenylalanine solutions. The objective of this review is to portray the many effects that increased phenylalanine availability has in plants under non-stressed conditions, focusing mainly on external applications. These applications include spraying and drenching whole plants with phenylalanine solutions, postharvest treatments by dipping fruit and cut flower stems, and addition of phenylalanine to cell suspensions. The results of these treatments include increased fragrance in flowers, increased aroma and pigmentation in fruit, increased production of health promoting metabolites in plant cell cultures, and increased resistance of plants, pre- and post-harvest, to a wide variety of pathogens. These effects suggest that plants can very efficiently uptake phenylalanine from their roots, leaves, flowers and fruits, translocate it from one organ to the other and between cell compartments, and metabolize it into phenylpropanoids. The mechanisms by which Phe treatment increases plant resistance to pathogens reveal new roles of phenylpropanoids in induction of genes related to the plant immune system. The simplicity of treatments with phenylalanine open many possibilities for industrial use. Many of the phenylalanine-treatment effects on increased resistance to plant pathogens have also been successful in commercial field trials.

Over 1000-Fold Synergistic Boost in Viniferin Levels by Elicitation of Vitis vinifera cv. Gamay Red Cell Cultures over Accumulating Phenylalanine

Elicitation treatments of grape cell cultures with methyl jasmonate (MeJA), ultraviolet-C (UV-C) irradiation, and sucrose induce mild production of stilbenes and flavonoids due to limited substrate availability. However, these treatments cause a synergistic boost of stilbenes production when applied to two phenylalanine (Phe)-enriched transgenic grape cell lines, AroG* + STS and AroG* + FLS. The combined treatment of UV-C elicitation on the Phe-fed AroG* + STS line resulted in the highest content of stilbenes (37.8-fold increase, 17.39 mg/g dry weight (DW)) mainly due to resveratrol (64-fold, 3.23 mg/g DW) and viniferin (1343-fold, 13.43 mg/g DW). The synergistic increase following either UV-C or MeJA elicitation was due to the induction of stilbene-related genes, while sucrose treatment had no effect on gene expression levels and served as an additional carbon source for phenylpropanoids. The combined strategy presented may enable future usage of grape cell cultures for the production of stilbenes and in particular viniferin.

A Synchronized Increase of Stilbenes and Flavonoids in Metabolically Engineered Vitis vinifera cv. Gamay Red Cell Culture

Stilbenes and flavonoids are two major health-promoting phenylpropanoid groups in grapes. Attempts to promote the accumulation of one group usually resulted in a decrease in the other. This study presents a unique strategy for simultaneously increasing metabolites in both groups in V. vinifera cv. Gamay Red grape cell culture, by overexpression of flavonol synthase (FLS) and increasing Phe availability. Increased Phe availability was achieved by transforming the cell culture with a second gene, the feedback-insensitive E. coli DAHP synthase (AroG*), and feeding them with Phe. A combined metabolomic and transcriptomic analysis reveals that the increase in both phenylpropanoid groups is accompanied by an induction of many of the flavonoid biosynthetic genes and no change in the expression levels of stilbene synthase. Furthermore, FLS overexpression with increased Phe availability resulted in higher anthocyanin levels, mainly those derived from delphinidin, due to the induction of F3'5'H. These insights may contribute to the development of grape berries with increased health benefits.

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

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

Metabolic Engineering Strategy Enables a Hundred-Fold Increase in Viniferin Levels in Vitis vinifera cv. Gamay Red Cell Culture

Stilbenes are phytoalexins with health-promoting benefits for humans. Here, we boost stilbenes' production, and in particular the resveratrol dehydrodimer viniferin, with significant pharmacological properties, by overexpressing stilbene synthase (STS) under unlimited phenylalanine (Phe) supply. Vitis vinifera cell cultures were co-transformed with a feedback-insensitive E. coli DAHP synthase (AroG*) and STS genes, under constitutive promoters. All transgenic lines had increased levels of Phe and stilbenes (74-fold higher viniferin reaching 0.74 mg/g DW). External Phe feeding of AroG* + STS lines caused a synergistic effect on resveratrol and viniferin accumulation, achieving a 26-fold (1.33 mg/g DW) increase in resveratrol and a 620-fold increase (6.2 mg/g DW) in viniferin, which to date is the highest viniferin accumulation reported in plant cultures. We suggest that this strategy of combining higher Phe availability and STS expression generates grape cell cultures as potential factories for sustainable production of stilbenes with a minor effect on the levels of flavonoids.

Induced defense response in red mango fruit against Colletotrichum gloeosporioides

Mango fruit exposed to sunlight develops red skin and are more resistant to biotic and abiotic stresses. Here we show that harvested red mango fruit that was exposed to sunlight at the orchard is more resistant than green fruit to Colletotrichum gloeosporioides. LCMS analysis showed high amounts of antifungal compounds, as glycosylated flavonols, glycosylated anthocyanins, and mangiferin in red vs. green mango skin, correlated with higher antioxidant and lower ROS. However, also the green side of red mango fruit that has low levels of flavonoids was resistant, indicated induced resistance. Transcriptomes of red and green fruit inoculated on their red and green sides with C. gloeosporioides were analyzed. Overall, in red fruit skin, 2,187 genes were upregulated in response to C. gloeosporioides. On the green side of red mango, upregulation of 22 transcription factors and 33 signaling-related transcripts indicated induced resistance. The RNA-Seq analysis suggests that resistance of the whole red fruit involved upregulation of ethylene, brassinosteroid, and phenylpropanoid pathways. To conclude, red fruit resistance to fungal pathogen was related to both flavonoid toxicity and primed resistance of fruit that was exposed to light at the orchard.

Phenylalanine increases chrysanthemum flower immunity against Botrytis cinerea attack

Flowers are the most vulnerable plant organ to infection by the necrotrophic fungus Botrytis cinerea. Here we show that pre-treatment of chrysanthemum (Chrysanthemum morifolium) flowers with phenylalanine (Phe) significantly reduces their susceptibility to B. cinerea. To comprehend how Phe treatment induces resistance, we monitored the dynamics of metabolites (by GC/LC-MS) and transcriptomes (by RNAseq) in flowers after Phe treatment and B. cinerea infection. Phe treatment resulted in accumulation of 3-phenyllactate and benzaldehyde, and in particular induced the expression of genes related to Ca²⁺ signaling and receptor kinases, implicating an induction of the defense response. Interestingly, the main effects of Phe treatment were observed in flowers exposed to B. cinerea infection, stabilizing the global fluctuations in the levels of metabolites and transcripts while reducing susceptibility to the fungus. We suggest that Phe-induced resistance is associated to cell priming, enabling rapid and targeted reprogramming of cellular defense responses to resist disease development. After Phe pre-treatment, the levels of the anti-fungal volatiles phenylacetaldehyde and eugenol were maintained and the level of coniferin, a plausible monolignol precursor in cell wall lignification, was strongly increased. In addition, Phe pre-treatment reduced ROS generation, prevented ethylene emission, and caused changes in the expression of a minor number of genes related to cell wall biogenesis, encoding the RLK THESEUS1, or involved in Ca²⁺ and hormonal signaling processes. Our findings point to Phe pre-treatment as a potential orchestrator of a broad-spectrum defense response which may not only provide an ecologically friendly pest control strategy but also offers a promising way of priming plants to induce defense responses against B. cinerea.

Increased phenylalanine levels in plant leaves reduces susceptibility to Botrytis cinerea

Botrytis cinerea is a major plant pathogen, causing losses in crops during growth and storage. Here we show that increased accumulation of phenylalanine (Phe) and Phe-derived metabolites in plant leaves significantly reduces their susceptibility to B. cinerea. Arabidopsis, petunia and tomato plants were enriched with Phe by either overexpressing a feedback-insensitive E.coli DAHP synthase (AroG*), or by spraying or drenching detached leaves or whole plants with external Phe, prior to infection with B. cinerea. Metabolic analysis of Arabidopsis and petunia plants overexpressing AroG* as well as wt petunia plants treated externally with Phe, revealed an increase in Phe-derived phenylpropanoids accumulated in their leaves, and specifically in those inhibiting B. cinerea germination and growth, suggesting that different compounds reduce susceptibility to B. cinerea in different plants. Phe itself had no inhibitory effect on germination or growth of B. cinerea, and inhibition of Phe metabolism in petunia plants treated with external Phe prevented decreased susceptibility to the fungus. Thus, Phe metabolism into an array of metabolites, unique to each plant and plant organ, is the most probable cause for increased resistance to Botrytis. This mechanism may provide a basis for ecologically friendly control of a wide range of plant pathogens.

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

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

Nutritional value of potato (Solanum tuberosum) in hot climates: anthocyanins, carotenoids, and steroidal glycoalkaloids

Growth in hot climates selectively alters potato tuber secondary metabolism-such as the anthocyanins, carotenoids, and glycoalkaloids-changing its nutritive value and the composition of health-promoting components. Potato breeding for improved nutritional value focuses mainly on increasing the health-promoting carotenoids and anthocyanins, and controlling toxic steroidal glycoalkaloids (SGAs). Metabolite levels are genetically determined, but developmental, tissue-specific, and environmental cues affect their final content. Transcriptomic and metabolomic approaches were applied to monitor carotenoid, anthocyanin, and SGA metabolite levels and their biosynthetic genes' expression under heat stress. The studied cultivars differed in tuber flesh carotenoid concentration and peel anthocyanin concentration. Gene expression studies showed heat-induced downregulation of specific genes for SGA, anthocyanin, and carotenoid biosynthesis. KEGG database mapping of the heat transcriptome indicated reduced gene expression for specific metabolic pathways rather than a global heat response. Targeted metabolomics indicated reduced SGA concentration, but anthocyanin pigments concentration remained unchanged, probably due to their stabilization in the vacuole. Total carotenoid level did not change significantly in potato tuber flesh, but their composition did. Results suggest that growth in hot climates selectively alters tuber secondary metabolism, changing its nutritive value and composition of health-promoting components.

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

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

Phenylpyruvate Contributes to the Synthesis of Fragrant Benzenoid-Phenylpropanoids in Petunia × hybrida Flowers

Phenylalanine (Phe) is a precursor for a large group of plant specialized metabolites, including the fragrant volatile benzenoid-phenylpropanoids (BPs). In plants, the main pathway leading to production of Phe is via arogenate, while the pathway via phenylpyruvate (PPY) is considered merely an alternative route. Unlike plants, in most microorganisms the only pathway leading to the synthesis of Phe is via PPY. Here we studied the effect of increased PPY production in petunia on the formation of BPs volatiles and other specialized metabolites originating from Phe both in flowers and leaves. Stimulation of the pathway via PPY was achieved by transforming petunia with PheA^∗ , a gene encoding a bacterial feedback insensitive bi-functional chorismate mutase/prephenate dehydratase enzyme. PheA^∗ overexpression caused dramatic increase in the levels of flower BP volatiles such as phenylacetaldehyde, benzaldehyde, benzyl acetate, vanillin, and eugenol. All three BP pathways characterized in petunia flowers were stimulated in PheA^∗ flowers. In contrast, PheA^∗ overexpression had only a minor effect on the levels of amino acids and non-volatile metabolites both in the leaves and flowers. The one exception is a dramatic increase in the level of rosmarinate, a conjugate between Phe-derived caffeate and Tyr-derived 3,4-dihydroxyphenylacetate, in PheA^∗ leaves. PheA^∗ petunia flowers may serve as an excellent system for revealing the role of PPY in the production of BPs, including possible routes directly converting PPY to the fragrant volatiles. This study emphasizes the potential of the PPY route in achieving fragrance enhancement in flowering plants.

An Intracellular Laccase Is Responsible for Epicatechin-Mediated Anthocyanin Degradation in Litchi Fruit Pericarp

In contrast to the detailed molecular knowledge available on anthocyanin synthesis, little is known about its catabolism in plants. Litchi (Litchi chinensis) fruit lose their attractive red color soon after harvest. The mechanism leading to quick degradation of anthocyanins in the pericarp is not well understood. An anthocyanin degradation enzyme (ADE) was purified to homogeneity by sequential column chromatography, using partially purified anthocyanins from litchi pericarp as a substrate. The purified ADE, of 116 kD by urea SDS-PAGE, was identified as a laccase (ADE/LAC). The full-length complementary DNA encoding ADE/LAC was obtained, and a polyclonal antibody raised against a deduced peptide of the gene recognized the ADE protein. The anthocyanin degradation function of the gene was confirmed by its transient expression in tobacco (Nicotiana benthamiana) leaves. The highest ADE/LAC transcript abundance was in the pericarp in comparison with other tissues, and was about 1,000-fold higher than the polyphenol oxidase gene in the pericarp. Epicatechin was found to be the favorable substrate for the ADE/LAC. The dependence of anthocyanin degradation by the enzyme on the presence of epicatechin suggests an ADE/LAC epicatechin-coupled oxidation model. This model was supported by a dramatic decrease in epicatechin content in the pericarp parallel to anthocyanin degradation. Immunogold labeling transmission electron microscopy suggested that ADE/LAC is located mainly in the vacuole, with essential phenolic substances. ADE/LAC vacuolar localization, high expression levels in the pericarp, and high epicatechin-dependent anthocyanin degradation support its central role in pigment breakdown during pericarp browning.

Metabolic Engineering of the Phenylpropanoid and Its Primary, Precursor Pathway to Enhance the Flavor of Fruits and the Aroma of Flowers

Plants produce a diverse repertoire of specialized metabolites that have multiple roles throughout their life cycle. Some of these metabolites are essential components of the aroma and flavor of flowers and fruits. Unfortunately, attempts to increase the yield and prolong the shelf life of crops have generally been associated with reduced levels of volatile specialized metabolites and hence with decreased aroma and flavor. Thus, there is a need for the development of new varieties that will retain their desired traits while gaining enhanced scent and flavor. Metabolic engineering holds great promise as a tool for improving the profile of emitted volatiles of domesticated crops. This mini review discusses recent attempts to utilize metabolic engineering of the phenylpropanoid and its primary precursor pathway to enhance the aroma and flavor of flowers and fruits.

Phenylalanine and tyrosine levels are rate-limiting factors in production of health promoting metabolites in Vitis vinifera cv. Gamay Red cell suspension

Environmental stresses such as high light intensity and temperature cause induction of the shikimate pathway, aromatic amino acids (AAA) pathways, and of pathways downstream from AAAs. The induction leads to production of specialized metabolites that protect the cells from oxidative damage. The regulation of the diverse AAA derived pathways is still not well understood. To gain insight on that regulation, we increased AAA production in red grape Vitis vinifera cv. Gamay Red cell suspension, without inducing external stress on the cells, and characterized the metabolic effect of this induction. Increased AAA production was achieved by expressing a feedback-insensitive bacterial form of 3-deoxy- D-arabino-heptulosonate 7-phosphate synthase enzyme (AroG (*)) of the shikimate pathway under a constitutive promoter. The presence of AroG(*) protein led to elevated levels of primary metabolites in the shikimate and AAA pathways including phenylalanine and tyrosine, and to a dramatic increase in phenylpropanoids. The AroG (*) transformed lines accumulated up to 20 and 150 fold higher levels of resveratrol and dihydroquercetin, respectively. Quercetin, formed from dihydroquercetin, and resveratrol, are health promoting metabolites that are induced due to environmental stresses. Testing the expression level of key genes along the stilbenoids, benzenoids, and phenylpropanoid pathways showed that transcription was not affected by AroG (*). This suggests that concentrations of AAAs, and of phenylalanine in particular, are rate-limiting in production of these metabolites. In contrast, increased phenylalanine production did not lead to elevated concentrations of anthocyanins, even though they are also phenylpropanoid metabolites. This suggests a control mechanism of this pathway that is independent of AAA concentration. Interestingly, total anthocyanin concentrations were slightly lower in AroG(*) cells, and the relative frequencies of the different anthocyanins changed as well.

In planta anthocyanin degradation by a vacuolar class III peroxidase in Brunfelsia calycina flowers

In contrast to detailed knowledge regarding the biosynthesis of anthocyanins, the largest group of plant pigments, little is known about their in planta degradation. It has been suggested that anthocyanin degradation is enzymatically controlled and induced when beneficial to the plant. Here we investigated the enzymatic process in Brunfelsia calycina flowers, as they changed color from purple to white. We characterized the enzymatic process by which B. calycina protein extracts degrade anthocyanins. A candidate peroxidase was partially purified and characterized and its intracellular localization was determined. The transcript sequence of this peroxidase was fully identified. A basic peroxidase, BcPrx01, is responsible for the in planta degradation of anthocyanins in B. calycina flowers. BcPrx01 has the ability to degrade complex anthocyanins, it co-localizes with these pigments in the vacuoles of petals, and both the mRNA and protein levels of BcPrx01 are greatly induced parallel to the degradation of anthocyanins. Both isoelectric focusing (IEF) gel analysis and 3D structure prediction indicated that BcPrx01 is cationic. Identification of BcPrx01 is a significant breakthrough both in the understanding of anthocyanin catabolism in plants and in the field of peroxidases, where such a consistent relationship between expression levels, in planta subcellular localization and activity has seldom been demonstrated.

Enhanced formation of aromatic amino acids increases fragrance without affecting flower longevity or pigmentation in Petunia × hybrida

Purple Petunia × hybrida V26 plants accumulate fragrant benzenoid-phenylpropanoid molecules and anthocyanin pigments in their petals. These specialized metabolites are synthesized mainly from the aromatic amino acids phenylalanine. Here, we studied the profile of secondary metabolites of petunia plants, expressing a feedback-insensitive bacterial form of 3-deoxy-di-arabino-heptulosonate 7-phosphate synthase enzyme (AroG*) of the shikimate pathway, as a tool to stimulate the conversion of primary to secondary metabolism via the aromatic amino acids. We focused on specialized metabolites contributing to flower showy traits. The presence of AroG* protein led to increased aromatic amino acid levels in the leaves and high phenylalanine levels in the petals. In addition, the AroG* petals accumulated significantly higher levels of fragrant benzenoid-phenylpropanoid volatiles, without affecting the flowers' lifetime. In contrast, AroG* abundance had no effect on flavonoids and anthocyanins levels. The metabolic profile of all five AroG* lines was comparable, even though two lines produced the transgene in the leaves, but not in the petals. This implies that phenylalanine produced in leaves can be transported through the stem to the flowers and serve as a precursor for formation of fragrant metabolites. Dipping cut petunia stems in labelled phenylalanine solution resulted in production of labelled fragrant volatiles in the flowers. This study emphasizes further the potential of this metabolic engineering approach to stimulate the production of specialized metabolites and enhance the quality of various plant organs. Furthermore, transformation of vegetative tissues with AroG* is sufficient for induced production of specialized metabolites in organs such as the flowers.

Do vacuolar peroxidases act as plant caretakers?

Plant vacuolar peroxidases catalyze the reduction of toxic H(2)O(2) accumulated in the vacuoles by oxidizing a variety of secondary metabolites. The redundancy of peroxidases and their ability to react with a wide range of substrates have prevented the observation of a clear phenotypic effect by modifying a single gene. Here we review the correlative and partial data on vacuolar peroxidases, including evidence for genes encoding vacuolar localized peroxidases, and indications of peroxidase activity in the vacuole. Based on these data, we suggest that these enzymes are key players in the adaptation of plants to change and serve as plant caretakers. At the cellular level, peroxidases protect the plant by scavenging excess H(2)O(2) that accumulates in the vacuoles under stressful conditions. At the tissue level, they are responsible for the last steps in the synthesis of the phytoalexins that often accumulate following pathogen attack of the plant tissue. At the whole-plant level, we suggest that peroxidases are involved in controlling the quality and quantity of light reaching the photosynthetic apparatus as plants adapt to lower light intensities. Further characterization of peroxidases, based on high-throughput genomic and metabolomic data, will help elucidate the mechanisms by which plants adapt to change.

ANTHOCYANIN1 from Solanum chilense is more efficient in accumulating anthocyanin metabolites than its Solanum lycopersicum counterpart in association with the ANTHOCYANIN FRUIT phenotype of tomato

Anthocyanins are flavonoid metabolites contributing attractive colors and antioxidant qualities to the human diet. Accordingly, there is a growing interest in developing crops enriched with these compounds. Fruits of the cultivated tomato, Solanum (S.) lycopersicum, do not normally produce high levels of anthocyanins. However, several wild tomato species yield anthocyanin-pigmented fruits, and this trait has been introgressed into the cultivated tomato. Two genes encoding homologous R2R3 MYB transcription factors, termed ANT1 and AN2, were previously genetically implicated in anthocyanin accumulation in tomato fruit peels of the ANTHOCYANIN FRUIT (AFT) genotype originating from S. chilense. Here we compared transgenic tomato plants constitutively over-expressing the S. lycopersicum (35S::ANT1 ( L ) ) or the S. chilense (35S::ANT1 ( C )) allele, and show that each displayed variable levels of purple pigmentation in vegetative as well as reproductive tissues. However, 35S::ANT1 ( C ) was significantly more efficient in producing anthocyanin pigments, attributed to its gene coding-sequence rather than to its transcript levels. These results expand the potential of enhancing anthocyanin levels through engineering coding-sequence polymorphisms in addition to the transcriptional alterations commonly used. In addition, a segregating population obtained from a recombinant genotype revealed that the native ANT1, and not AN2, is fully associated with the AFT phenotype and that ANT1 alone can generate the characteristic phenotype of anthocyanin accumulation in AFT fruits. Our results therefore provide further support to the hypothesis that ANT1 is the gene responsible for anthocyanin accumulation in fruits of the AFT genotype.

Increased accumulation and decreased catabolism of anthocyanins in red grape cell suspension culture following magnesium treatment

Anthocyanins are the largest and best studied group of plant pigments. However, not very much is known about the fate of these phenolic pigments after they have accumulated in the cell vacuoles of plant tissues. We have previously shown that magnesium treatment of ornamentals during the synthesis of anthocyanins in the flowers or foliage caused an increase in the pigment concentration. In this study, we characterized the effect of magnesium on the accumulation of anthocyanin in red cell suspension originating from Vitis vinifera cv. Gamay Red grapes. Magnesium treatment of the cells caused a 2.5- to 4.5-fold increase in anthocyanin concentration, with no substantial induction of the biosynthetic genes. This treatment inhibited the degradation of anthocyanins occurring in the cells, and changed the ratio between different anthocyanins determining cell color, with an increase in the relative concentration of the less stable pigment molecules. The process by which magnesium treatment affects anthocyanin accumulation is still not clear. However, the results presented suggest at least part of its effect on anthocyanin accumulation stems from inhibition of the pigments' catabolism. When anthocyanin biosynthesis was inhibited, magnesium treatments prevented the constant degradation of anthocyanins in the cell suspension. Future understanding of the catabolic processes undergone by anthocyanins in plants may enable more efficient inhibition of this process and increased accumulation of these pigments, and possibly of additional phenolic compounds.

Metabolic networking in Brunfelsia calycina petals after flower opening

Brunfelsia calycina flowers change colour from purple to white due to anthocyanin degradation, parallel to an increase in fragrance and petal size. Here it was tested whether the production of the fragrant benzenoids is dependent on induction of the shikimate pathway, or if they are formed from the anthocyanin degradation products. An extensive characterization of the events taking place in Brunfelsia flowers is presented. Anthocyanin characterization was performed using ultraperfomance liquid chromatography-quadrupole time of flight-tandem mass specrometry (UPLC-QTOF-MS/MS). Volatiles emitted were identified by headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Accumulated proteins were identified by 2D gel electrophoresis. Transcription profiles were characterized by cross-species hybridization of Brunfelsia cDNAs to potato cDNA microarrays. Identification of accumulated metabolites was performed by UPLC-QTOF-MS non-targeted metabolite analysis. The results include characterization of the nine main anthocyanins in Brunfelsia flowers. In addition, 146 up-regulated genes, 19 volatiles, seven proteins, and 17 metabolites that increased during anthocyanin degradation were identified. A multilevel analysis suggests induction of the shikimate pathway. This pathway is the most probable source of the phenolic acids, which in turn are precursors of both the benzenoid and lignin production pathways. The knowledge obtained is valuable for future studies on degradation of anthocyanins, formation of volatiles, and the network of secondary metabolism in Brunfelsia and related species.

Characterization of the intense pigment tomato genotype emphasizing targeted fruit metabolites and chloroplast biogenesis

The tomato INTENSE PIGMENT (IP) genotype is characterized by intense visual pigmentation of unripe and ripe fruits, not thoroughly analyzed thus far. This study was therefore designed to analyze key morphologic, metabolomic, and photomorphogenic phenotypes of this genotype in comparison to its near-isogenic normal counterpart and to evaluate its significance relative to other tomato mutants known for increased fruit pigmentation. The IP genotype produced smaller and darker red fruits, and a substantially increased chloroplast biogenesis was found in its green fruit and leaf tissues. Ripe-red fruits of the IP genotype produced 34-38% more soluble solids and up to 62.6% more carotenoids, but no differences were found in the concentration of flavonoid compounds in its peel tissue. The IP genotype was found to display a greater hypocotyl inhibition response to blue and yellow light, but a more prominent and novel response to total darkness. As a whole, the IP genotype exhibited highly desirable traits, making it a valuable genotype for tomato breeders attempting to introduce functional and taste qualities into tomato fruits.

Molecular aspects of Anthocyanin fruit tomato in relation to high pigment-1

The tomato Anthocyanin fruit (Aft) genotype is characterized by purple color in skin and outer pericarp of its fruits due to higher levels of anthocyanins-flavonoid metabolites. Our objectives were to carry out metabolic and molecular characterization of this genotype, emphasizing its interaction with the high pigment-1 (hp-1) mutation, known to increase flavonoids in tomato fruits. These objectives fit the growing interest in developing tomato fruits with higher levels of functional metabolites. Our results show that 1) Aft fruits are also characterized by significantly higher levels of the flavonols quercetin and kaempferol, thus enhancing their functional value; 2) the tomato Anthocyanin1 (Ant1) gene, encoding a Myb transcription factor, displayed nucleotide and amino acid polymorphisms between the Aft genotype and cultivated genotypes; 3) a DNA marker based on Ant1 showed that the Aft trait is encoded by a single locus on chromosome 10 fully associated with Ant1; and 4) double homozygotes Aft/Aft hp-1/hp-1 plants displayed a more-than-additive effect on the production of fruit anthocyanidins and flavonols. This effect was manifested by approximately 5-, 19-, and 33-fold increase of petunidin, malvidin, and delphinidin, respectively, in the double mutants compared with the cumulative levels of their parental lines.

Active anthocyanin degradation in Brunfelsia calycina (yesterday--today--tomorrow) flowers

Anthocyanins are the largest group of plant pigments responsible for colors ranging from red to violet and blue. The biosynthesis of anthocyanins, as part of the larger phenylpropanoid pathway, has been characterized in great detail. In contrast to the detailed molecular knowledge available on anthocyanin synthesis, very little is known about the stability and catabolism of anthocyanins in plants. In this study we present a preliminary characterization of active in planta degradation of anthocyanins, requiring novel mRNA and protein synthesis, in Brunfelsia calycina flowers. Brunfelsia is a unique system for this study, since the decrease in pigment concentration in its flowers (from dark purple to white) is extreme and rapid, and occurs at a specific and well-defined stage of flower development. Treatment of detached flowers with protein and mRNA synthesis inhibitors, at specific stages of flower development, prevented degradation. In addition, treatment of detached flowers with cytokinins delayed senescence without changing the rate of anthocyanin degradation, suggesting that degradation of anthocyanins is not part of the general senescence process of the flowers but rather a distinctive and specific pathway. Based on studies on anthocyanin degradation in wine and juices, peroxidases are reasonable candidates for the in vivo degradation. A significant increase in peroxidase activity was shown to correlate in time with the rate of anthocyanin degradation. An additional indication that oxidative enzymes are involved in the process is the fact that treatment of flowers with reducing agents, such as DTT and glutathione, caused inhibition of degradation. This study represents the first step in the elucidation of the molecular mechanism behind in vivo anthocyanin degradation in plants.

The A locus that controls anthocyanin accumulation in pepper encodes a MYB transcription factor homologous to Anthocyanin2 of Petunia

Pepper plants containing the dominant A gene accumulate anthocyanin pigments in the foliage, flower and immature fruit. We previously mapped A to pepper chromosome 10 in the F(2) progeny of a cross between 5226 (purple-fruited) and PI 159234 (green-fruited) to a region that corresponds, in tomato, to the location of Petunia anthocyanin 2 ( An2), a regulator of anthocyanin biosynthesis. This suggested that A encodes a homologue of Petunia An2. Using the sequences of An2 and a corresponding tomato expressed sequence tag, we isolated a pepper cDNA orthologous to An2 that cosegregated with A. We subsequently determined the expression of A by Northern analysis, using RNA extracted from fruits, flowers and leaves of 5226 and PI 159234. In 5226, expression was detected in all stages of fruit development and in both flower and leaf. In contrast, A was not expressed in the sampled tissues in PI 159234. Genomic sequence comparison of A between green- and purple-fruited genotypes revealed no differences in the coding region, indicating that the lack of expression of A in the green genotypes can be attributed to variation in the promoter region. By analyzing the expression of the structural genes in the anthocyanin biosynthetic pathway in 5226 and PI 159234, it was determined that, similar to Petunia, the early genes in the pathway are regulated independently of A, while expression of the late genes is A-dependent.

Increased anthocyanin accumulation in aster flowers at elevated temperatures due to magnesium treatment

Temperature is one of the main external factors affecting anthocyanin accumulation in plant tissues: low temperatures cause an increase and elevated temperatures cause a decrease in anthocyanin concentration. Several metals have been shown to increase the half-life time of anthocyanins, by forming complexes with them. We studied the combined effect of elevated temperatures and increased metal concentrations on the accumulation of anthocyanins in aster 'Sungal' flowers. It has been found that magnesium treatment of aster plants or detached flower buds, partially prevents colour fading at elevated temperatures. Anthocyanin concentration of aster 'Sungal' flowers grown at 29 degrees C/21 degrees C day/night, respectively, was about half that of flowers grown at 17 degrees C/9 degrees C. The activity of phenylalanine ammonia-lyase (PAL) and chalcone isomerase (CHI) decreased as the temperature increased. Treatment of both whole plants and detached flower buds grown at elevated temperatures in the presence of magnesium salts, increased flower anthocyanin concentration by up to 80%. Measurement of magnesium following these treatments revealed an increased level of the metal in the petals, suggesting a direct effect. Magnesium treatment does not seem to cause increased synthesis of anthocyanin through a stress-related reaction, since the activities of both PAL and CHI did not increase due to this treatment. The results of this study show that increasing magnesium levels in aster petals prevents the deleterious effect of elevated temperatures on anthocyanin accumulation, thus enhancing flower colour.

Isolation and spectroscopic characterization of a plantlike photosystem II reaction center from the cyanobacterium Synechocystis sp. 6803

A chlorophyll-protein complex has been isolated from the cyanobacterium Synechocystis sp. PCC 6803 that closely resembles higher plant photosystem II reaction centers in spectral properties. The Synechocystis complex has a pigment content of 5-7 chlorophyll a molecules:1 Cyt b559:2 pheophytins; an optical absorption redmost transition at approximately 675 nm; and a nonconservative circular dichroism red signal, with extrema at 682 (+) and 652 (-) nm. Upon illumination, the Synechocystis D1/D2/Cyt b559 complex accumulates reduced pheophytin. LDS-PAGE and/or immunoblotting showed the D1, D2, and Cyt b559 proteins, aggregated and degraded forms of D1 and possibly D2, and traces of ATP synthase and the CP47 photosystem II chlorophyll protein. The availability of such a Synechocystis preparation opens the way for employing site-directed mutagenesis in studying primary reactions of oxygenic photosynthesis.

The D-E region of the D1 protein is involved in multiple quinone and herbicide interactions in photosystem II

The region between helices D and E (D-E region) of the D1 protein of photosystem II (PSII) is exposed at the stromal side of the photosynthetic membrane, contains the secondary plastoquinone (QB) binding niche, and is involved in processes at the reducing side of PSII. The role of the D-E region was studied in 27 site-directed mutants generated in the psbAII gene of the cyanobacterium Synechocystis sp. PCC 6803. The photochemical performance of the modified PSII reaction centers was assessed with respect to photoautotrophic growth, oxygen evolution, fluorescence induction, and herbicide inhibition. A few mutations, located at positions presumably involved in essential interactions in the QB binding niche, greatly interfered with PSII performance. On the other hand, mutations in the presumptive loop region between helices D and de resulted in relatively minor effects, indicating a flexible region not critical for photochemical function. Indeed, although more than 80% of the D-E region is phylogenetically invariant, the bulk of the mutations affected the measured parameters only moderately. The significance of the conserved residues appears to be in subtle interactions that optimize the thermodynamic balance between some of the redox components of PSII, as indicated by mild changes in the steady state fluorescence. Many mutations modified tolerances to PSII herbicides. The dispersion of these mutations throughout the D-E region indicates the complex nature of the interactions, direct and indirect, affecting herbicide binding in the QB niche. Mutation of codons Ser221 and Ser222 to Leu221 and Ala222 revealed a new location coordinating the herbicide diuron in the D1 protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein modifications in the D2 protein of photosystem II affect properties of the QB/herbicide-binding environment

The D2 protein contains an extended loop (the D-de loop) between helices D and de at the reducing side of photosystem II (PS II). Characterization of D2 mutants of the cyanobacterium Synechocystis sp. PCC 6803 has indicated that the length and amino acid composition of the D-de loop are not critical for basic PS II functions, although most of the residues in that region are conserved phylogenetically. Here we show using herbicide binding and electron-flow inhibition measurements that drastic modifications in the D-de loop of the D2 protein modify the interaction of some PS II-directed herbicides with their binding niche. The stability of (semi)-reduced QB in its binding pocket is altered in at least two of the mutants, as indicated by a shifted peak temperature of the thermoluminescence signal originating from charge recombination involving QB. These results suggest a close functional association between the D-de loop of the D2 protein and the QB/herbicide-binding environment, which is viewed as being coordinated mostly by residues of the D1 protein. This represents one of the first examples of modification of the QB/herbicide-binding domain by mutations in the D2 protein.

Occurrence of the chromoplast protein ChrA correlates with a fruit-color gene in Capsicum annuum

Plant geneticists have determined that the color of ripe fruits of sweet peppers (Capsicum annuum L.) is determined by four genes: y, c1, c2 and cl. We have compared the electrophoretic behavior of chromoplast membrane proteins of seven varieties of C. annuum which differ in these genes. ChrA was detected only in the varieties that had a y+ genotype, and was not affected by variations in the other three genes. The identity of ChrA was verified by probing blots of SDS gels with antiserum to ChrA. The second known chromoplast-specific protein, ChrB, was found to be independent of all four genes. No proteins correlating with c1, c2 or cl were detected in either one- or two-dimensional gels.

Plasma membrane potential of the alga dunaliella, and its relation to osmoregulation

A fluorescent dye sensitive to membrane potential was used to follow the plasma-membrane potential in the unicellular halo-tolerant alga Dunaliella salina. The signal observed during dissipation of the plasma membrane potential by the addition of excess K(+) and valinomycin, or a protonophore, was taken as a measure of the preexisting potential. A resting potential of -85 to -100 millivolts (negative inside) was calculated. Following a hypertonic shock, the plasma membrane was rapidly hyperpolarized. This hyperpolarization was transient, and the algae resumed their resting potential about 30 minutes after the shock. The resting plasma membrane potential was decreased by vanadate and is concluded to be generated mostly by the plasma membrane ATPase of Dunaliella. The transient hyperpolarization following a hypertonic shock indicates, therefore, a transient activation of the ATPase. This is further corroborated by a rapid transient decrease in the intracellular ATP following a hypertonic shock and its inhibition by vanadate. It is suggested that activation of the plasma membrane ATPase may be the trigger for osmoregulation in Dunaliella.

Involvement of the Plasma Membrane ATPase in the Osmoregulatory Mechanism of the Alga Dunaliella salina

The unicellular halotolerant alga Dunaliella salina recovers normally from a hypertonic shock even when suspended in NaCl and buffer only. Furthermore, addition of Cu(2+), valinomycin and KCl, or permeable ions such as methyltriphenylphosphonium or thiocyanate, do not affect the recovery. However, treatment with two specific inhibitors of the plasma membrane adenosine triphosphatase (ATPase), diethylstilbestrol, or vanadate, fully inhibit the recovery. The inhibition is manifested by the inability of the cells to both synthesize glycerol and return to their original volume. The inhibitions are nonlethal, reversible and equally effective in the dark or the light. Since the plasma membrane ATPase is the only enzyme known to be inhibited by both diethylstilbestrol and vanadate, it is concluded that its activity is essential for the recovery of Dunaliella from a hypertonic shock. Mechanisms by which the plasma membrane ATPase may participate in the activation of glycerol production in the algae are discussed.

P and C-NMR Studies of the Phosphorus and Carbon Metabolites in the Halotolerant Alga, Dunaliella salina

The intracellular phosphorus and carbon metabolites in the halotolerant alga Dunaliella salina adapted to different salinities were monitored in living cells by (31)P- and (13)C-nuclear magnetic resonance (NMR) spectroscopy. The (13)C-NMR studies showed that the composition of the visible intracellular carbon metabolites other than glycerol is not significantly affected by the salinity of the growth medium. The T(1) relaxation rates of the (13)C-glycerol signals in intact cells were enhanced with increasing salinity of the growth medium, in parallel to the expected increase in the intracellular viscosity due to the increase in intracellular glycerol. The (31)P-NMR studies showed that cells adapted to the various salinities contained inorganic phosphate, phosphomonoesters, high energy phosphate compounds, and long chain polyphosphates. In addition, cells grown in media containing up to 1 molar NaCl contained tripolyphosphates. The tripolyphosphate content was also controlled by the availability of inorganic phosphate during cell growth. Phosphate-depleted D. salina contained no detectable tripolyphosphate signal. Excess phosphate, however, did not result in the appearance of tripolyphosphate in (31)P-NMR spectra of cells adapted to high (>1.5 molar NaCl) salinites.