The involvement of cyclotides in the heavy metal tolerance of Viola spp.

The Violaceae family is rich in metal-tolerant species and species producing cyclic peptides (cyclotides) that are linked to the resistance to biotic factors. Plants that inhabit areas polluted with heavy metals have developed various mechanisms of tolerance. To test the role of cyclotides in protection against abiotic factors, including heavy metals, cell suspension cultures of Viola species/genotypes (V. lutea ssp. westfalica, V. tricolor, V. arvensis, and V. uliginosa), representing different levels of tolerance to heavy metals (from the most tolerant-MET to the least tolerant populations/species-NMET), were used. The relative abundances of the cyclotides in the control, untreated cell suspensions of all the selected species/genotypes, and cells treated with Zn or Pb (200 µM or 2000 µM) for 24 h or 72 h were determined via MALDI-MS. Transmission electron microscopy with X-ray microanalysis was used to detect putative co-localization of the cyclotides with Zn or Pb in the cells of V. tricolor treated with the highest concentration of heavy metals for 72 h. Cyclotide biosynthesis was dependent on the type of heavy metal and its concentration, time of treatment, plant species, and population type (MET vs. NMET). It was positively correlated with the level of tolerance of particular Viola species. The increased production of cyclotides was observed in the cells of metallophyte species, mostly in Zn-treated cells. The nonmetallophyte-V. uliginosa presented a decrease in the production of cyclotides independent of the dose and duration of the metal treatment. Cyclotides co-localized with Pb more evidently than with Zn, suggesting that cyclotides have heavy metal affinity. V. lutea ssp. westfalica transcriptome mining yielded 100 cyclotide sequences, 16 known and 84 novel named viwe 1-84. These findings support the hypothesis that cyclotides are involved in certain mechanisms of plant tolerance to heavy metals.

Gene-guided identifications of a structure-chimeric cyclotide viphi I from Viola philippica: Potential functions against cadmium and nematodes.

The cyclic peptides, cyclotides, are identified mostly with 29-31-aa (amino acid residues) but rarely with ≥ 34-aa in plants. Viola philippica is a well-known medicinal plant but a rare metallophyte with cyclotides. A hypothesis was hence raised that the potential novel 34-aa cyclotide of Viola philippica would clearly broaden the structural and functional diversities of plant cyclotides. After homology-cloning the cyclotide precursor gene of VpCP5, a 34-aa cyclotide (viphi I) was identified to be larger than 22 other known cyclotides in V. philippica. It had a chimeric primary structure, due to its unusual loop structures (8 residues in loop 2 and 6 residues in loop 5) and aa composition (3 E and 5 R), by using phylogenetic analyses and an in-house cyclotide analysis tool, CyExcel_V1. A plasmid pCYC-viphi_I and a lab-used recombinant process were specially constructed for preparing viphi I. Typically, 0.12 or 0.25 mg ml-1 co-exposed viphi I could significantly remain cell activities with elevating Cd2+-exposed doses from 10-8 to 10-6 mol l-1 in MCF7 cells. In the model nematode Caenorhabditis elegans, IC50 values of viphi I to inhibit adult ratios and to induce death ratios, were 184.7 and 585.9 µg ml-1, respectively; the median lifespan of adult worms decreased from 14 to 2 d at viphi I doses ranging from 0.05 to 2 mg ml-1. Taken together, the newly identified viphi I exhibits functional potentials against cadmium and nematodes, providing new insights into structural and functional diversity of chimeric cyclotides in plants.

Cyclotides derived from Viola dalatensis Gagnep: A novel approach for enrichment and evaluation of antimicrobial activity.

Cyclotides, plant-derived cysteine-rich peptides, exhibit a wide range of beneficial biological activities and possess exceptional structural stability. Cyclotides are commonly distributed throughout the Violaceae family. Viola dalatensis Gagnep, a Vietnamese species, has not been well studied, especially for cyclotides. This pioneering research explores cyclotides from V. dalatensis as antimicrobials. This study used a novel approach to enhance cyclotides after extraction. The approach combined 30% ammonium sulfate salt precipitation and RP-HPLC. A comprehensive analysis was performed to ascertain the overall protein content, flavonoids content, polyphenol content, and free radical scavenging capacity of compounds derived from V. dalatensis. Six known cyclotides were sequenced utilizing MS tandem. Semi-purified cyclotide mixtures (M1, M2, and M3) exhibited antibacterial efficacy against Bacillus subtilis (inhibitory diameters: 19.67-23.50 mm), Pseudomonas aeruginosa (22.17-23.50 mm), and Aspergillus flavus (14.67-21.33 mm). The enriched cyclotide precipitate from the stem extract demonstrated a minimum inhibitory concentration (MIC) of 0.08 mg/mL against P. aeruginosa, showcasing significant antibacterial effectiveness compared to the stem extract (MIC: 12.50 mg/mL). Considerable advancements have been achieved in the realm of cyclotides, specifically in their application as antimicrobial agents.

Morphological studies of self-assembled cyclotides extracted from Viola odorata as novel versatile platforms in biomedical applications.

Self-assembling peptides have attracted researchers' attention recently. They are classified as biomedical materials with unique properties formed in response to environmental conditions. Cyclotides are macrocyclic plant-derived peptides containing 28-37 amino acids that have the ability to self-assemble. Herein, we investigated the effect of pH, time, and temperature on the self-assembling properties of the cyclotides extracted from Viola odorata. For this purpose, the cyclotides were dispersed in aqueous trifluoroacetic acid at pH 2, 4, or 6 and incubated at 25 or 37 °C for 1, 2, 3, 5, 7 or 10 days, and the morphology of the self-assembled structures was identified by optical microscopy, polarized optical microscopy, scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. At pH 2 and 4, the self-assembly process of cyclotides comprises a number of steps, starting with the formation of spherical peptide nanostructures followed by hierarchically assembled nanotubes, and then shifting to nanofibers after 10 days. At pH 6, amorphous structures were produced even after 10 days. The temperature also could affect the self-assembly mechanism of the cyclotides. At 25 °C, the spherical peptide micelles formed firstly and then merged to form nanotubes, while at 37 °C the cyclotides showed crystallization followed by an increase in length with time. The fluorescence microscopy images showed that the nanotubes could efficiently entrap the hydrophobic molecules of coumarin. This comparative study on the self-assembly of the cyclotides extracted from Viola odorata is the first example exploring the capacity of these cyclotides to adopt precise nanostructures. The nanotubes and nanofibers obtained with these cyclotides might find interesting applications in drug delivery and tissue engineering.

The involvement of cyclotides in mutual interactions of violets and the two-spotted spider mite.

Plants employ different chemicals to protect themselves from herbivory. These defenses may be constitutive or triggered by stress. The chemicals can be toxic, act as repellents, phagosuppressants and/or phago-deterrents. The two-spotted spider mite (Tetranychus urticae) is a generalist arthropod herbivorous pest and its feeding causes extensive damage both to crops and wild plants. Cyclotides are cyclic peptides involved in host-plant defenses. A single Viola sp. can produce more than a hundred cyclotides with different biological activities and roles. The organ and tissue specific cyclotide patterns change over the seasons and/or with environment, but the role of biotic/abiotic stress in shaping them remains unclear. Here, we demonstrate the involvement of cyclotides in mutual interactions between violets and mites. We used immunohistochemistry and mass spectrometry imaging to show the ingested cyclotides in T. urticae and assess the Viola odorata response to mite feeding. Moreover, to assess how mites are affected by feeding on violets, acceptance and reproductive performance was compared between Viola uliginosa, V. odorata and Phaseolus vulgaris. We demonstrate that cyclotides had been taken in by mites feeding on the violets. The ingested peptides were found in contact with epithelial cells of the mite digestive system, in the fecal matter, feces, ovary and eggs. Mites preferred common bean plants (P. vulgaris) to any of the violet species; the latter affected their reproductive performance. The production of particular cyclotides in V. odorata (denoted by molecular weights: 2979, 3001, 3017, 3068, 3084, 3123) was activated by mite feeding and their levels were significantly elevated compared to the control after 5 and 21 days of infestation. Specific cyclotides may affect mites by being indigestible or through direct interaction with cells in the mite digestive tract and reproductive organs. A group of particular peptides in V. odorata appears to be involved in defense response against herbivores.

Tropical vibes from Sri Lanka - cyclotides from Viola betonicifolia by transcriptome and mass spectrometry analysis.

Cyclotides are an extremely stable class of peptides, ubiquitously distributed in Violaceae. The aim of the present study was to investigate the presence of cyclotides in Sri Lankan Violaceae plants, using combined tools of transcriptomics and mass spectrometry. New cyclotides were discovered for the first time in the wild flora of Sri Lanka, within Viola betonicifolia, a plant used in traditional medicine as an antimicrobial. Plant extracts prepared in small scale from Viola betonicifolia were first subjected to LC-MS analysis. Subsequent transcriptome de novo sequencing of Viola betonicifolia uncovered 25 new (vibe 1-25) and three known (varv A/kalata S, viba 17, viba 11) peptide sequences from Möbius and bracelet cyclotide subfamilies as well as hybrid cyclotides. Among the transcripts, putative linear acyclotide sequences (vibe 4, vibe 10, vibe 11 and vibe 22) that lack a conserved asparagine or aspartic acid vital for cyclisation were also present. Four asparagine endopeptidases (AEPs), VbAEP1-4 were found within the Viola betonicifolia transcriptome, including a peptide asparaginyl ligase (PAL), potentially involved in cyclotide backbone cyclisation, showing >93% sequence homology to Viola yedoensis peptide asparaginyl ligases, VyPALs. In addition, we identified two protein disulfide isomerases (PDIs), VbPDI1-2, likely involved in cyclotide oxidative folding, having high sequence homology (>74%) with previously reported Rubiaceae and Violaceae PDIs. The current study highlights the ubiquity of cyclotides in Violaceae as well as the utility of transcriptomic analysis for cyclotides and their putative processing enzyme discovery. The high variability of cyclotide sequences in terms of loop sizes and residues in V. betonicifolia showcase the cyclotide structure as an adaptable scaffold as well as their importance as a combinatorial library, implicated in plant defense.

Gibberellins are required for dimorphic flower development in Viola philippica.

Photoperiod is a major determinant of chasmogamous (CH)-cleistogamous (CL) dimorphic flower development in Viola philippica, and only long-day (LD) conditions induce CL flowers. In this study, it was found that the active gibberellin (GA) content in CL floral buds was higher than in CH floral buds formed under short-day (SD) conditions, suggesting that the biosynthesis of active GAs is enhanced by a longer photoperiod and may be associated with dimorphic flower development. Thus, the next step was to molecularly characterize the key V. philippica GA synthesis genes GA 20-oxidase (VpGA20ox) and GA 3-oxidase (VpGA3ox). In terms of the expression of VpGA20ox and VpGA3ox, it was found that the active GAs could be upregulated in developing pistils under both LD and SD conditions to develop functional pistils, and GAs could also accumulate in the stamens under SD conditions. The anthers and the adjacent petals were well developed under SD conditions. In contrast, the above-mentioned floral organs displayed low GA contents under LD conditions and were poorly developed. Although the application of paclobutrazol, an inhibitor of GA synthesis, did not reverse CL development under LD conditions, exogenous GAs could partially trigger the transition from CH to CL flowers under relative SD conditions (≤12 h daylight). This was coupled with the downregulation of B-class MADS-box genes, thereby restraining stamen and petal development. Both VpGA20ox and VpGA3ox exhibited similar expression profiles with B-class MADS-box genes in the development of the stamens and petals. Therefore, in response to photoperiod, GA signaling could affect the expression of B-class homeotic genes and regulate dimorphic flower development in Viola. As a compensation for poorly-developed nectaries, anthers, and petals, filament elongation, style shortness, and inward bending could ensure self-pollination in CL flowers. This work provides new insights into the regulation of CH-CL floral development and the evolutionary significance of the formation of dimorphic flowers.

Purification of the phytase enzyme from Lactobacillus plantarum: The effect on pansy growth and macro-micro element content.

In the present study, the phytase enzyme was purified from Lactobacillus plantarum with a 3.08% recovery, 9.57-purification fold, and with a specific activity of 278.82 EU/mg protein. Then, the effects of the 5 EU and 10 EU purified phytase was determined on the plant growth, quality, the macro-micro nutrient content of pansy (Viola × wittrockiana), which is of great importance in ornamental plants industry. The research was established under greenhouse conditions with natural light in 2017. The pansy seeds were coated with phytase enzyme solution, sown in a peat environment, and transferred to pots at the seedling period. In general, the 5 EU and 10 EU applications increase plant height, the number of leaves per plant, the number of side branches per plant, and flower height parameters compared to control. Also, micro- and macronutrient values in soil and plant samples were examined. According to the results, the phytase application on pansy cultivation positively affected the properties and yielded high quality of plants.

The life cycle of cyclotides: biosynthesis and turnover in plant cells.

KEY MESSAGE: Turnover rates have implications for understanding cyclotide biology and improving plant cell culture-based production systems. Cyclotides are a family of polypeptides recognized for a broad spectrum of bioactivities. The cyclic, cystine knot structural motif imparts these peptides with resistance to temperature, chemicals and proteolysis. Cyclotides are found widely distributed across the Violaceae and in five other plant families, where their presumed biological role is host defense. Violets produce mixtures of different cyclotides that vary depending on the organ, tissue or influence of environmental factors. In the present study, we investigated the biosynthesis and turnover of cyclotides in plant cells. Viola uliginosa suspension cultures were grown in media where all nitrogen containing salts were replaced with their 15N counterparts. This approach combined with LC-MS analysis allowed to separately observe the production of 15N-labelled peptides and decomposition of 14N cyclotides present in the cells when switching the media. Additionally, we investigated changes in cyclotide content in V. odorata germinating seeds. In the suspension cultures, the degradation rates varied for individual cyclotides and the highest was noted for cyO13. Rapid increase in production of 15N peptides was observed until day 19 and subsequently, a plateau of production, indicating an equilibrium between biosynthesis and turnover. The developing seedling appeared to consume cyclotides present in the seed endosperm. We show that degradation processes shape the cyclotide pattern present in different tissues and environments. The results indicate that individual cyclotides play different roles-some in defense and others as storage proteins. The turnover of cyclotides should be accounted to improve cell culture production systems.

Differences in the functioning of photosynthetic electron transport between metallicolous and non-metallicolous populations of the pseudometallophyte Viola tricolor.

The objective of this study was to assess the effect of metalliferous conditions on the functioning of photosynthetic electron transport in waste heap populations of a pseudometallophyte, Viola tricolor L. Measurements of chlorophyll a fluorescence and the absorbance changes at 830 nm enabled a non-invasive assessment of photosynthetic apparatus performance. This was complemented by the evaluation of the chlorophyll content. Low temperature chlorophyll fluorescence emission spectra were also recorded. Based on the OJIP test performed in situ, we demonstrated a disturbed condition of photosystem II (PSII) in three metalliferous populations in comparison with a non-metallicolous one. The combined effects of elevated concentrations of zinc, cadmium and lead in soil resulted in the decline of some parameters describing the efficiency and electron flow through PSII. The differences between waste heap populations seemed to be partly correlated with the concentration of heavy metals in the soil. The characteristic of electron transport at photosystem I (PSI) in the light-adapted state revealed increased values of PSI donor-side limitation (YND) and a declined PSI quantum efficiency (YI). It was also demonstrated that the waste heap conditions negatively affect the total chlorophyll content in leaves and led to an increased ratio of fluorescence emission at 77 K (F730/F685). The obtained data indicate that, regardless of the high adaptation of metallicolous populations, photosynthetic electron transport is hampered in V. tricolor plants at metal polluted sites.

Behavioral and physiological effects of Viola spp. cyclotides on Myzus persicae (Sulz.).

Cyclotides are defense peptides produced by several plant families. Viola spp. (Violaceae) produce an array of cyclotides with varying biological activities. The peach potato aphid Myzus persicae (Sulz.) (Hemiptera: Aphididae) is a generalist that feeds on the secondary hosts of over 40 plant families, including Violaceae. The present work aimed to evaluate the activities of cycloviolacins from Viola odorata L. and V. ulignosa Besser (cyO2, cyO3, cyO13, cyO19) against M. persicae. To investigate the peptides' influence on aphid feeding behavior, we used 20% sucrose diets supplemented with cyclotides and measured the effects with electrical penetration graph (EPG) technique. We also applied anti-cyclotide antibodies and immunohistochemistry to track the peptides in the digestive systems of the aphids. Our study shows that cyclotides affect aphid probing and feeding behavior and limit their diet sap uptake. The cycloviolacin cyclotides: cyO13 (100 µM) and cyO19 (50 µM) most strongly impeded aphid ingestion activities when applied in sucrose diet. Sustained ingestion of the diet was blocked by 100 µM cyO13, and no aphid showed ingestion of the diet for longer than 10 min. Cyclotides were detected in the pharynx, in contact with the epipharyngeal gustatory organ, in the stomach (midgut) and upper intestine. The present study shows the deterrent activity of cycloviolacins on M. persicae. This activity may be related to the peptides' effects on epithelial cells and gustatory organs along the aphid digestive system. We demonstrate that cyclotides may play an important role in plant-aphid interactions.

De novo transcriptome analysis of Viola ×wittrockiana exposed to high temperature stress.

Around the world, pansies are one of the most popular garden flowers, but they are generally sensitive to high temperatures, and this limits the practicality of planting them during the warmest days of the year. However, a few pansy germplasms with improved heat tolerance have been discovered or bred, but the mechanisms of their heat resistance are not understood. In this study, we investigated the transcript profiles of a heat-tolerant pansy inbred line, DFM16, in response to high temperatures using RNAseq. Approximately 55.48 Gb of nucleotide data were obtained and assembled into 167,576 unigenes with an average length of 959 bp, of which, 5,708 genes were found to be differentially expressed after heat treatments. Real-time qPCR was performed to validate the expression profiles of the selected genes. Nine metabolic pathways were found to be significantly enriched, in the analysis of the differentially expressed genes. Several potentially interesting genes that encoded putative transcription regulators or key components involving heat shock protein (HSP), heat shock transcription factors (HSF), and antioxidants biosynthesis, were identified. These genes were highlighted to indicate their significance in response to heat stress and will be used as candidate genes to improve pansy heat-tolerance in the future.

Comparative Transcriptomic Studies on a Cadmium Hyperaccumulator Viola baoshanensis and Its Non-Tolerant Counterpart V. inconspicua.

Many Viola plants growing in mining areas exhibit high levels of cadmium (Cd) tolerance and accumulation, and thus are ideal organisms for comparative studies on molecular mechanisms of Cd hyperaccumulation. However, transcriptomic studies of hyperaccumulative plants in Violaceae are rare. Viola baoshanensis is an amazing Cd hyperaccumulator in metalliferous areas of China, whereas its relative V. inconspicua is a non-tolerant accumulator that resides at non-metalliferous sites. Here, comparative studies by transcriptome sequencing were performed to investigate the key pathways that are potentially responsible for the differential levels of Cd tolerance between these two Viola species. A cascade of genes involved in the ubiquitin proteosome system (UPS) pathway were observed to have constitutively higher transcription levels and more activation in response to Cd exposure in V. baoshanensis, implying that the enhanced degradation of misfolded proteins may lead to high resistance against Cd in this hyperaccumulator. Many genes related to sucrose metabolism, especially those involved in callose and trehalose biosynthesis, are among the most differentially expressed genes between the two Viola species, suggesting a crucial role of sucrose metabolism not only in cell wall modification through carbon supply but also in the antioxidant system as signaling molecules or antioxidants. A comparison among transcriptional patterns of some known transporters revealed that several tonoplast transporters are up-regulated in V. baoshanensis under Cd stress, suggesting more efficient compartmentalization of Cd in the vacuoles. Taken together, our findings provide valuable insight into Cd hypertolerance in V. baoshanensis, and the corresponding molecular mechanisms will be useful for future genetic engineering in phytoremediation.

Deciphering the phylogeny of violets based on multiplexed genetic and metabolomic approaches.

Molecular phylogenetics based on nucleotide sequence comparisons has profoundly influenced plant taxonomy. A comprehensive chemotaxonomical approach based on GC-MS and UHPLC-HRMS profiling was evaluated for its ability to characterize a large collection of plants all in the violet family Violaceae (n = 111) and thus decipher the taxonomy. A thorough identification of violets is challenging due to their natural hybridization and phenotypic variability. Phylogenetic inference performed on ribosomal internal transcribed spacer sequences using maximum likelihood and neighbor-joining distance methods allowed the clear identification of 58% of the collection. Metabolomic approaches with multivariate data analysis were performed on SPME/GC-MS chromatograms of volatile compounds emitted by fresh mature flowers and on UHPLC-HRMS/MS leaf extracts for non-volatile compounds. Interestingly, molecular and biochemical approaches provided separate classifications while highlighting several common clusters. The profiling of secondary metabolites was proved most suitable for the classification of hundreds of extracts. The combination of phylogenetic and chemotaxonomic approaches, allowed the classification of 96% of the entire collection. A correlation network revealed specific chemotaxonomic biomarkers, in particular flavonoids, coumarins and cyclotides. Overall, our pioneering approach could be useful to solve misclassification issues within collections of close plant species.

Production of bioactive cyclotides in somatic embryos of Viola odorata.

Viola odorata L. (Violaceae), an Indian medicinal plant, contains a plethora of cyclotides, which are a class of cyclic peptides derived from plants, possessing several applications. Somatic embryo culture of V. odorata was developed, via indirect somatic embryogenesis, to serve as an alternative to natural plant biomass for sustainable and continuous production of its bioactive ingredients, such as cyclotides. Among the various combinations of phytohormones tested, Murashige and Skoog medium supplemented with 1 mg/l thidiazuron gave rise to the maximum frequency of induction (86.7%) and a high number of somatic embryos (3) from an embryogenic callus. Identification and characterization of cyclotides in the somatic embryos were carried out using a Fourier transform mass spectrometer coupled with liquid chromatography (LC-FTMS). Among the cyclotides identified in the study, few were found to be exclusively present in the somatic embryo culture. Furthermore, the relative abundance of the cyclotides was higher in somatic embryo extract than in the natural plant extract. The biological activities (cytotoxic, haemolytic and antimicrobial) of the somatic embryos and the parent plant were compared. Unlike the natural plants, the somatic embryo extracts demonstrated specificity i.e. they were found to be potent against cancerous cells but not against non-cancerous cell line or red blood cells. In contrast to the plant extract, the somatic embryos extracts were found to be potent against Escherichia coli and Staphylococcus aureus. These results suggest that somatic embryos of V. odorata (rich in cyclotides) can be used as an alternative to plant biomass for its therapeutic applications and germplasm conservation.

Tyramine and tyrosine decarboxylase gene contributes to the formation of cyanic blotches in the petals of pansy (Viola × wittrockiana).

Tyrosine decarboxylase (TYDC) can catalyze tyrosine into tyramine. Several studies demonstrated its roles in the acidity, salidroside and defense response. Here we found that TYDC from Viola × wittrockiana Gam (VwTYDC) may contribute to the formation of cyaninc blotches in the petal. VwTYDC gene were cloned from Viola × wittrockiana and the cDNA full-length sequences were 1634 bp encoding 494 amino acids. Gene expression of VwTYDC in different tissues and developmental stages showed that they were significantly higher expressed in flowers than stems, leaves and roots. In addition, VwTYDC expression were higher in cyanic blotches than those observed in acyanic blotches of petal. Metabolites analysis showed the contents of tyramine in cyanic blotches were also higher than that in acyanic areas. Furthermore, in vitro assay revealed the absorption peak of anthocyanins had a red shift and an increase when fed tyramine. We speculated that tyramine might contribute to flower color expression of pansy as co-pigment. Our study demonstrated for the first time that the contents of tyramine led to flower blotches formation in cyanic blotches of the petals in plant flowers, and this may due to the higher expression of VwTYDC gene.

A molecular dynamics strategy for CSαß peptides disulfide-assisted model refinement.

Many cysteine-stabilized antimicrobial peptides from a variety of living organisms could be good candidates for the development of anti-infective agents. In the absence of experimentally obtained structural data, peptide modeling is an essential tool for understanding structure-activity relationships and for optimizing the bioactive moieties. Focusing on cysteine-rich peptide structures, we reproduced the case of structure predictions in the so-called midnight zone. We developed our protocol on a training set derived by clustering the available cysteine-stabilized αß (CSαß) structures in nine different representative families and tested it on peptides randomly selected from each family. Starting from draft models, we tested a structure-based disulfide predictor and we used cysteine distances as constraints during molecular dynamics. Finally, we proposed an analysis for final structure selection. Accordingly, we obtained a mean root mean square deviation improvement of 21% for the test set. Our findings demonstrate that it is possible to predict the network of disulfide bridges in cysteine-stabilized peptides and to use this result to improve the accuracy of structural predictions. Finally, we applied the methods to predict the structure of royalisin, a cysteine-rich peptide with unknown structure.

Expression of B-class MADS-box genes in response to variations in photoperiod is associated with chasmogamous and cleistogamous flower development in Viola philippica.

BACKGROUND: Some plants develop a breeding system that produces both chasmogamous (CH) and cleistogamous (CL) flowers. However, the underlying molecular mechanism remains elusive. RESULTS: In the present study, we observed that Viola philippica develops CH flowers with short daylight, whereas an extended photoperiod induces the formation of intermediate CL and CL flowers. In response to long daylight, the respective number and size of petals and stamens was lower and smaller than those of normally developed CH flowers, and a minimum of 14-h light induced complete CL flowers that had no petals but developed two stamens of reduced fertility. The floral ABC model indicates that B-class MADS-box genes largely influence the development of the affected two-whorl floral organs; therefore, we focused on characterizing these genes in V. philippica to understand this particular developmental transition. Three such genes were isolated and respectively designated as VpTM6-1, VpTM6-2, and VpPI. These were differentially expressed during floral development (particularly in petals and stamens) and the highest level of expression was observed in CH flowers; significantly low levels were detected in intermediate CL flowers, and the lowest level in CL flowers. The observed variations in the levels of expression after floral induction and organogenesis apparently occurred in response to variations in photoperiod. CONCLUSIONS: Therefore, inhibition of the development of petals and stamens might be due to the downregulation of B-class MADS-box gene expression by long daylight, thereby inducing the generation of CL flowers. Our work contributes to the understanding of the adaptive evolutionary formation of dimorphic flowers in plants.

Metabolomics for the Authentication of Natural Extracts Used in Flavors and Fragrances: the Case Study of Violet Leaf Absolutes from Viola odorata.

Natural extracts used in fine fragrances (alcoholic perfumes) are rare and precious. As such, they represent an interesting target for fraudulent practices called adulterations. Absolutes, important materials used in the creation of perfumes, are obtained by organic solvent extraction of raw plant materials. Because the nonvolatile part of these natural extracts is not normalized and scarcely reported, highlighting potential adulterations present in this fraction appears highly challenging. For the first time, we investigated the use of nontargeted UHPLC-ToFMS metabolomics for this purpose, considering Viola odorata l., a plant largely used in the perfume industry, as a model. Significant differences in the metabolic fingerprints of the violet leaf absolutes were evidenced according to geographical locations, and/or adulterations. Additionally, markers of the geographical origin were detected through their molecular weight/most probable molecular formula and retention time, while adulterations were statistically validated. In this study, we thus clearly demonstrated the efficiency of UHPLC-ToFMS-based metabolomics in accelerating both the identification of the origin of raw materials as well as the search for potential adulterations in absolutes, natural products of high added value.

Exogenous plant hormones and cyclotide expression in Viola uliginosa (Violaceae).

Plants from Violaceae produce cyclotides, peptides characterized by a circular peptide backbone and a cystine knot. This signature motif gives stability that can harness a wide spectrum of biological activities, with implications in plant defense and with applications in medicine and biotechnology. In the current work, cyclotide expressing in vitro cultures were established from Viola uliginosa. These cultures are useful models for studying biosynthesis of cyclotides and can also be used in their production. The cyclotide expression pattern is shown to be dependent on exogenous plant growth regulators, both on peptide and gene expression levels. The highest yields of cyclotides were obtained on media containing only a cytokinin and were correlated with storage material accumulation. Exposure to auxins decreased cyclotide production and caused shifting of the biosynthesis pattern to root specific cyclotides. The response to stimuli in terms of cyclotide expression pattern appears to be developmental, and related to polar auxin transportation and the auxin/cytokinin ratio regulating tissue differentiation. By the use of whole transcriptome shotgun sequencing (WTSS) and peptidomics, 20 cyclotide sequences from V. uliginosa (including 12 new) and 12 complete precursor proteins could be identified. The most abundant cyclotides were cycloviolacin O3 (CyO3), CyO8 and CyO13. A suspension culture was obtained that grew exponentially with a doubling time of approximately 3 days. After ten days of growth, the culture provided a yield of more than 4 mg CyO13 per gram dry mass.