Production of glucosinolates, phenolic compounds and associated gene expression profiles of hairy root cultures in turnip (Brassica rapa ssp. rapa)

Reynoutria japonica Houtt. Transformed Hairy Root Cultures as an Effective Platform for Producing Phenolic Compounds with Strong Bactericidal Properties

Reynoutria japonica Houtt. is the source of various phenolic compounds: phenolic acids, flawan-3-ols, and stilbenes, with a broad range of biological activity. The rhizome (underground organ of these plants) is abundant in secondary metabolites but, in natural conditions, may accumulate various toxic substances (such as heavy metals) from the soil. The principal objective of this research was to produce transformed cultures of R. japonica hairy roots that would serve as a valuable source of phenolic compounds, independent of environmental resources. The transformation was performed using a variety of wild strains of Rhizobium rhizogenes bacteria, of which only strain A4 (ATCC 31798) proved effective. The molecular characterization of transformed clones was performed using PCR. The biometric parameters (growth index and dry weight content), phenolic compounds accumulation (DAD-HPLC), antioxidant capacity (DPPH, CUPRAC), and bactericidal properties against Staphylococcus aureus with various sensitivity to antibiotics were evaluated. Two obtained transformed clones (RJ 9 and 30) exhibited the incorporation of the entire bacterial T-DNA into genomic DNA, while clones RJ 10 and 11 demonstrated only the presence of the LT-DNA sequence. The results demonstrated an increase in flawan-3-ols (catechins) accumulation in hairy root tissue relative to non-transformed (NT) plants. Moreover, hairy roots exhibited enhanced antioxidant activity and bactericidal properties compared with NT roots and NT shoots, respectively.

Production of Phenolic Compounds and Antioxidant Activity in Hairy Root Cultures of Salvia plebeia

Salvia plebeia (Lamiaceae) is a medicinal plant containing diverse bioactive constituents that have biological properties. In this study, we determined the optimal conditions (media and auxin) for the hairy root culture of S. plebeia for the growth and accumulation of phenolic compounds and evaluated its antioxidant activities. Rosmarinic acid and five phenylpropanoids were detected using high-performance liquid chromatography. The hairy roots grown in 1/2 SH medium with 1 mg/L NAA had a high level of rosmarinic acid content. Hairy roots cultured in 1 mg/L NAA had the highest total content of five phenylpropanoids. Compared to wild-type roots grown in the field, hairy roots (NAA 1) expressed similar levels of rosmarinic acid but significantly enhanced phenylpropanoid accumulation. Furthermore, the total phenolic content and total flavonoid content of hairy roots (NAA 1) were 2.22 and 1.73 times higher than those of wild-type roots. In the results of DPPH, ABTS, and reducing power assays, the hairy roots (NAA 1) showed higher free radical scavenging effects and reduction potential than the wild-type roots. These results suggest that S. plebeia hairy roots cultured under optimal conditions, which exhibit enhanced phenolic compound accumulation and antioxidant activity, can potentially be used as sources of antioxidants.

Enhanced Production of Nitrogenated Metabolites with Anticancer Potential in Aristolochia manshuriensis Hairy Root Cultures

Aristolochia manshuriensis is a relic liana, which is widely used in traditional Chinese herbal medicine and is endemic to the Manchurian floristic region. Since this plant is rare and slow-growing, alternative sources of its valuable compounds could be explored. Herein, we established hairy root cultures of A. manshuriensis transformed with Agrobacterium rhizogenes root oncogenic loci (rol)B and rolC genes. The accumulation of nitrogenous secondary metabolites significantly improved in transgenic cell cultures. Specifically, the production of magnoflorine reached up to 5.72 mg/g of dry weight, which is 5.8 times higher than the control calli and 1.7 times higher than in wild-growing liana. Simultaneously, the amounts of aristolochic acids I and II, responsible for the toxicity of Aristolochia species, decreased by more than 10 fold. Consequently, the hairy root extracts demonstrated pronounced cytotoxicity against human glioblastoma cells (U-87 MG), cervical cancer cells (HeLa CCL-2), and colon carcinoma (RKO) cells. However, they did not exhibit significant activity against triple-negative breast cancer cells (MDA-MB-231). Our findings suggest that hairy root cultures of A. manshuriensis could be considered for the rational production of valuable A. manshuriensis compounds by the modification of secondary metabolism.

Accumulation of phenolic compounds and expression of phenylpropanoid biosynthesis-related genes in leaves of basil transformed with A. rhizogenes strains

Biotic factors affect the content of secondary metabolites by interfering with molecular and biochemical pathways. In the current study, A. rhizogenes strains were inoculated into basil (Ocimum basilicum) to examine the effect of plant-microbe interaction on the accumulation of monomeric phenolic metabolites and the transcript levels of selected genes involved in the biochemical synthesis of secondary compounds. Initially, the integration of the rolB gene was validated by performing PCR analysis on genomic DNA samples from the basil plant inoculated with A. rhizogenes strains. We have detected that the accumulation of mRNA transcripts linked to the biosynthesis pathway of phenolic compounds has higher transcript expression levels in the leaves of transformed basil in proportion to uninoculated plants. Basil plants inoculated with A. rhizogenes 39207 strain had higher transcript levels of CAD, C4H, TAT, FLS, EGS, HPPR, PAL, and RAS genes than other experimental groups. We have identified eleven phenolic components, and the level of rosmarinic acid, eugenol, chicoric acid, and rutin increased in the inoculated basil leaves. However, the inoculation of A. rhizogenes did not cause a change in the compounds of chlorogenic acid, methyl chavicol, cinnamic acid, quercetin, vanillic acid, and caffeic acid. In conclusion, the increase in basic secondary metabolites could be achieved by the A. rhizogenes-mediated transformation of basil plants, and especially ATCC 43057 strain may be one of the A. rhizogenes strains.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01320-w.

Impact of Light and Dark Treatment on Phenylpropanoid Pathway Genes, Primary and Secondary Metabolites in Agastache rugosa Transgenic Hairy Root Cultures by Overexpressing Arabidopsis Transcription Factor AtMYB12

Agastache rugosa, otherwise called Korean mint, has a wide range of medicinal benefits. In addition, it is a rich source of several medicinally valuable compounds such as acacetin, tilianin, and some phenolic compounds. The present study aimed to investigate how the Tartary buckwheat transcription factor AtMYB12 increased the primary and secondary metabolites in Korean mint hairy roots cultured under light and dark conditions. A total of 50 metabolites were detected by using high-performance liquid chromatography (HPLC) and gas chromatography-time-of-flight mass spectrometry (GC-TOFMS). The result showed that the AtMYB12 transcription factor upregulated the phenylpropanoid biosynthesis pathway genes, which leads to the highest accumulation of primary and secondary metabolites in the AtMYB12-overexpressing hairy root lines (transgenic) than that of the GUS-overexpressing hairy root line (control) when grown under the light and dark conditions. However, when the transgenic hairy root lines were grown under dark conditions, the phenolic and flavone content was not significantly different from that of the control hairy root lines. Similarly, the heat map and hierarchical clustering analysis (HCA) result showed that most of the metabolites were significantly abundant in the transgenic hairy root cultures grown under light conditions. Principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) showed that the identified metabolites were separated far based on the primary and secondary metabolite contents present in the control and transgenic hairy root lines grown under light and dark conditions. Metabolic pathway analysis of the detected metabolites showed 54 pathways were identified, among these 30 were found to be affected. From these results, the AtMYB12 transcription factor activity might be light-responsive in the transgenic hairy root cultures, triggering the activation of the primary and secondary metabolic pathways in Korean mint.

Hairy Root Cultures as a Source of Phenolic Antioxidants: Simple Phenolics, Phenolic Acids, Phenylethanoids, and Hydroxycinnamates

Plant-derived antioxidants are intrinsic components of human diet and factors implicated in tolerance mechanisms against environmental stresses in both plants and humans. They are being used as food preservatives and additives or ingredients of cosmetics. For nearly forty years, Rhizobium rhizogenes-transformed roots (hairy roots) have been studied in respect to their usability as producers of plant specialized metabolites of different, primarily medical applications. Moreover, the hairy root cultures have proven their value as a tool in crop plant improvement and in plant secondary metabolism investigations. Though cultivated plants remain a major source of plant polyphenolics of economic importance, the decline in biodiversity caused by climate changes and overexploitation of natural resources may increase the interest in hairy roots as a productive and renewable source of biologically active compounds. The present review examines hairy roots as efficient producers of simple phenolics, phenylethanoids, and hydroxycinnamates of plant origin and summarizes efforts to maximize the product yield. Attempts to use Rhizobium rhizogenes-mediated genetic transformation for inducing enhanced production of the plant phenolics/polyphenolics in crop plants are also mentioned.

Differences in pseudogene evolution contributed to the contrasting flavors of turnip and Chiifu, two Brassica rapa subspecies

Pseudogenes are important resources for investigation of genome evolution and genomic diversity because they are nonfunctional but have regulatory effects that influence plant adaptation and diversification. However, few systematic comparative analyses of pseudogenes in closely related species have been conducted. Here, we present a turnip (Brassica rapa ssp. rapa) genome sequence and characterize pseudogenes among diploid Brassica species/subspecies. The results revealed that the number of pseudogenes was greatest in Brassica oleracea (CC genome), followed by B. rapa (AA genome) and then Brassica nigra (BB genome), implying that pseudogene differences emerged after species differentiation. In Brassica AA genomes, pseudogenes were distributed asymmetrically on chromosomes because of numerous chromosomal insertions/rearrangements, which contributed to the diversity among subspecies. Pseudogene differences among subspecies were reflected in the flavor-related glucosinolate (GSL) pathway. Specifically, turnip had the highest content of pungent substances, probably because of expansion of the methylthioalkylmalate synthase-encoding gene family in turnips; these genes were converted into pseudogenes in B. rapa ssp. pekinensis (Chiifu). RNA interference-based silencing of the gene encoding 2-oxoglutarate-dependent dioxygenase 2, which is also associated with flavor and anticancer substances in the GSL pathway, resulted in increased abundance of anticancer compounds and decreased pungency of turnip and Chiifu. These findings revealed that pseudogene differences between turnip and Chiifu influenced the evolution of flavor-associated GSL metabolism-related genes, ultimately resulting in the different flavors of turnip and Chiifu.

The effect of chitosan and β-cyclodextrin on glucosinolate biosynthesis in Brassica rapa ssp. pekinensis (Chinese cabbage) shoot culture

Chitosan is a polycationic polysaccharide derived from chitin, and β-cyclodextrin is a type of macrocyclic oligosaccharide linked by α-1,4 glycosidic bonds. These compounds are recognized as effective elicitors in the biosynthesis of secondary metabolites in plants. These elicitors were studied to assess the growth of shoots and the synthesis of glucosinolates (GSLs) from elicited shoots in Chinese cabbage under controlled in vitro conditions for the first time. Chitosan at 150 mg L^-1 supplemented in the optimized shoot induction recovered maximum quantities of total GSLs (7.344 μmol g^-1 DW) at the end of 5th week of culture duration, followed by β-cyclodextrin (15 mg L^-1) with the synthesis of GSLs (6.379 μmol g^-1 DW) at the end of 4th week of culture. The application of chitosan completely deteriorated the growth of shoots, whereas β-cyclodextrin did not affect and even increased the growth of shoots (4.66 g DW). Upon elicitation, the individual got GSLs contents exhibited various fold changes (1.78-to-23.5-fold). Real-time PCR analysis of essential GSLs biosynthesis genes like MAM1, ST5b, AOP2, FMOGS-OX1, CYP83B1, CYP81F2, ST5a, and CYP81F4 revealed substantial higher expression upon elicitation. This present study would provide a steady production of GSLs in Chinese cabbage shoots with the influence of carbohydrate-based elicitors for pharmaceutical or food companies in the future.

Production and Biomedical Applications of Bioactive Compounds

The development of drug resistance to presently available synthetic medicines leads us to investigate naturally produced small bioactive molecules to treat drug-resistant diseases, such as cancer and other diseases [...]

Characterization of anti-proliferative and anti-oxidant effects of nano-sized vesicles from Brassica oleracea L. (Broccoli)

In this in vitro study, we test our hypothesis that Broccoli-derived vesicles (BDVs), combining the anti-oxidant properties of their components and the advantages of their structure, can influence the metabolic activity of different cancer cell lines. BDVs were isolated from homogenized fresh broccoli (Brassica oleracea L.) using a sucrose gradient ultracentrifugation method and were characterized in terms of physical properties, such as particle size, morphology, and surface charge by transmission electron microscopy (TEM) and laser doppler electrophoresis (LDE). Glucosinolates content was assessed by RPLC–ESI–MS analysis. Three different human cancer cell lines (colorectal adenocarcinoma Caco-2, lung adenocarcinoma NCI-H441 and neuroblastoma SHSY5Y) were evaluated for metabolic activity by the MTT assay, uptake by fluorescence and confocal microscopy, and anti-oxidant activity by a fluorimetric assay detecting intracellular reactive oxygen species (ROS). Three bands were obtained with average size measured by TEM based size distribution analysis of 52 nm (Band 1), 70 nm (Band 2), and 82 nm (Band 3). Glucobrassicin, glucoraphanin and neoglucobrassicin were found mostly concentrated in Band 1. BDVs affected the metabolic activity of different cancer cell lines in a dose dependent manner compared with untreated cells. Overall, Band 2 and 3 were more toxic than Band 1 irrespective of the cell lines. BDVs were taken up by cells in a dose- and time-dependent manner. Pre-incubation of cells with BDVs resulted in a significant decrease in ROS production in Caco-2 and NCI-H441 stimulated with hydrogen peroxide and SHSY5Y treated with 6-hydroxydopamine, with all three Bands. Our findings open to the possibility to find a novel “green” approach for cancer treatment, focused on using vesicles from broccoli, although a more in-depth characterization of bioactive molecules is warranted.

Hairy Root Cultures as a Source of Polyphenolic Antioxidants: Flavonoids, Stilbenoids and Hydrolyzable Tannins

Due to their chemical properties and biological activity, antioxidants of plant origin have gained interest as valuable components of the human diet, potential food preservatives and additives, ingredients of cosmetics and factors implicated in tolerance mechanisms against environmental stress. Plant polyphenols are the most prominent and extensively studied, albeit not only group of, secondary plant (specialized) metabolites manifesting antioxidative activity. Because of their potential economic importance, the productive and renewable sources of the compounds are desirable. Over thirty years of research on hairy root cultures, as both producers of secondary plant metabolites and experimental systems to investigate plant biosynthetic pathways, brought about several spectacular achievements. The present review focuses on the Rhizobium rhizogenes-transformed roots that either may be efficient sources of plant-derived antioxidants or were used to elucidate some regulatory mechanisms responsible for the enhanced accumulation of antioxidants in plant tissues.

Plant Nutrition for Human Health: A Pictorial Review on Plant Bioactive Compounds for Sustainable Agriculture

Is there any relationship between plant nutrition and human health? The overall response to this question is very positive, and a strong relationship between the nutrition of plants and humans has been reported in the literature. The nutritional status of edible plants consumed by humans can have a negative or positive impact on human health. This review was designed to assess the importance of plant bioactive compounds for human health under the umbrella of sustainable agriculture. With respect to the first research question, it was found that plant bioactives (e.g., alkaloids, carotenoids, flavonoids, phenolics, and terpenoids) have a crucial role in human health due to their therapeutic benefits, and their potentiality depends on several factors, including botanical, environmental, and clinical attributes. Plant bioactives could be produced using plant tissue culture tools (as a kind of agro-biotechnological method), especially in cases of underexploited or endangered plants. Bioactive production of plants depends on many factors, especially climate change (heat stress, drought, UV radiation, ozone, and elevated CO2), environmental pollution, and problematic soils (degraded, saline/alkaline, waterlogged, etc.). Under the previously mentioned stresses, in reviewing the literature, a positive or negative association was found depending on the kinds of stress or bioactives and their attributes. The observed correlation between plant bioactives and stress (or growth factors) might explain the importance of these bioactives for human health. Their accumulation in stressed plants can increase their tolerance to stress and their therapeutic roles. The results of this study are in keeping with previous observational studies, which confirmed that the human nutrition might start from edible plants and their bioactive contents, which are consumed by humans. This review is the first report that analyzes this previously observed relationship using pictorial presentation.

Preventive effects of Brassicaceae family for colon cancer prevention: A focus on in vitro studies

The emergence of adverse effects and resistance to colorectal cancer (CRC) current therapies calls for the development of new strategies aimed at both preventing and treating. In this context, functional extracts from Brassicaceae family contains abundant bioactive compounds directly related to a positive effect on human health including cancer. The main objective of this systematic review is to compile all recent studies that analyzed the in vitro antiproliferative activity of functional extracts or isolated molecules from the Brassicaceae family against CRC. A total of 711 articles published between January 2011 and May 2021 were identified. Of them, 68 met our inclusion criteria. Different standardized protocols using variable parts of plants of the Brassicaceae family resulted in diverse bioactive extracts and/or compounds. Most of them were related to isothiocyanates, which showed significant antitumor activity against CRC. These in vitro studies provide an excellent guide to direct research on the applications of plants of the Brassicaceae family to the prevention of this type of tumor. The extracts and molecules with demonstrated activity against CRC should be tested in vivo and in clinical trials to determine their usefulness in the prevention of this cancer to reduce its global incidence.

Transcriptomics Integrated with Metabolomics Unveil Carotenoids Accumulation and Correlated Gene Regulation in White and Yellow-Fleshed Turnip (Brassica rapa ssp. rapa)

Turnip (Brassica rapa ssp. rapa) is considered to be a highly nutritious and health-promoting vegetable crop, whose flesh color can be divided into yellow and white. It is widely accepted that yellow-fleshed turnips have higher nutritional value. However, reports about flesh color formation is lacking. Here, the white-fleshed inbred line, W21, and yellow-fleshed inbred line, W25, were profiled from the swollen root of the turnip at three developmental periods to elucidate the yellow color formation. Transcriptomics integrated with metabolomics analysis showed that the PSY gene was the key gene affecting the carotenoids formation in W25. The coding sequence of BrrPSY-W25 was 1278 bp and that of BrrPSY-W21 was 1275 bp, and BrrPSY was more highly expressed in swollen roots in W25 than in W21. Transient transgenic tobacco leaf over-expressing BrrPSY-W and BrrPSY-Y showed higher transcript levels and carotenoids contents. Results revealed that yellow turnip formation is due to high expression of the PSY gene rather than mutations in the PSY gene, indicating that a post-transcriptional regulatory mechanism may affect carotenoids formation. Results obtained in this study will be helpful for explaining the carotenoids accumulation of turnips.

Phyto-factories of anti-cancer compounds: a tissue culture perspective

Background

Cancer is one of the most critical but ubiquitous causes of death grappled from past decades. Widely used chemotherapy with cytotoxic activity blocks/ kills the cancer cell. The compounds targeted for anticancerous activity are either derived synthetically or naturally (through plants or microbial origin). Current day, versatile role of plants in medicinal field has been attributed to the secondary metabolites it produces, known for their anticancer activity. Therefore, discovery, identification and commercial production of such novel anticancer drugs is escalated and are centerpiece for pharmaceuticals.

Main body

A biotechnological approach, principally tissue culture, leads the candidacy to be an alternative method for production of anticancer compounds. A wide range of bioactive agents like alkaloids, steroids, phenolics, saponins, flavonoids, and terpenoids are in huge demand commercially. Plant tissue culture applications are constructively more advantageous over conventional methods in terms of their continuous, controlled, aseptic production, large scale and de novo synthesis opportunity. Various bioreactors are used for mass cultivation of bioactive compound at commercial level. For example: stirred tank reactors are used for production of shikonin from Lithospermum erythrorhizon, vincristine from Catharanthus roseus, podophyllotoxin from Podophyllum etc. Strategies like callus culture, suspension culture and hairy root culture are opted for mass cultivation of these bioactives.

Conclusions

This review summarizes plant tissue culture as a promising strategy proven to be a colossal breakthrough in reliable and continuous production of existing and novel anticancer compounds and help in combating the increasing future demands.

Agronomic and Metabolomic Side-Effects of a Divergent Selection for Indol-3-Ylmethylglucosinolate Content in Kale (Brassica oleracea var. acephala)

Brassica oleracea var. acephala (kale) is a cruciferous vegetable widely cultivated for its leaves and flower buds in Europe and a food of global interest as a “superfood”. Brassica crops accumulate phytochemicals called glucosinolates (GSLs) which play an important role in plant defense against biotic stresses. Studies carried out to date suggest that GSLs may have a role in the adaptation of plants to different environments, but direct evidence is lacking. We grew two kale populations divergently selected for high and low indol-3-ylmethylGSL (IM) content (H-IM and L-IM, respectively) in different environments and analyzed agronomic parameters, GSL profiles and metabolomic profile. We found a significant increase in fresh and dry foliar weight in H-IM kale populations compared to L-IM in addition to a greater accumulation of total GSLs, indole GSLs and, specifically, IM and 1-methoxyindol-3-ylmethylGSL (1MeOIM). Metabolomic analysis revealed a significant different concentration of 44 metabolites in H-IM kale populations compared to L-IM. According to tentative peak identification from MS interpretation, 80% were phenolics, including flavonoids (kaempferol, quercetin and anthocyanin derivates, including acyl flavonoids), chlorogenic acids (esters of hydroxycinnamic acids and quinic acid), hydroxycinnamic acids (ferulic acid and p-coumaric acid) and coumarins. H-IM kale populations could be more tolerant to diverse environmental conditions, possibly due to GSLs and the associated metabolites with predicted antioxidant potential.

BrLETM2 Protein Modulates Anthocyanin Accumulation by Promoting ROS Production in Turnip (Brassica rapa subsp. rapa)

In ‘Tsuda’ turnip, the swollen root peel accumulates anthocyanin pigments in a light-dependent manner, but the mechanism is unclear. Here, mutant g120w which accumulated extremely low levels of anthocyanin after light exposure was identified. Segregation analysis showed that the anthocyanin-deficient phenotype was controlled by a single recessive gene. By using bulked-segregant analysis sequencing and CAPS marker-based genetic mapping analyses, a 21.6-kb region on chromosome A07 was mapped, in which a calcium-binding EF hand family protein named BrLETM2 was identified as the causal gene. RNA sequencing analysis showed that differentially expressed genes (DEGs) between wild type and g120w in light-exposed swollen root peels were enriched in anthocyanin biosynthetic process and reactive oxygen species (ROS) biosynthetic process GO term. Furthermore, nitroblue tetrazolium (NBT) staining showed that the ROS level decreased in g120w mutant. Anthocyanins induced by UV-A were abolished by the pre-treatment of seedlings with DPI (an inhibitor of nicotinamide adenine nucleoside phosphorylase (NADPH) oxidase) and decreased in g120w mutant. These results indicate that BrLETM2 modulates ROS signaling to promote anthocyanin accumulation in turnip under UV-A and provides new insight into the mechanism of how ROS and light regulate anthocyanin production.

ADAP is a possible negative regulator of glucosinolate biosynthesis in Arabidopsis thaliana based on clustering and gene expression analyses

Glucosinolates (GSLs) are plant secondary metabolites consisting of sulfur and nitrogen, commonly found in Brassicaceae crops, such as Arabidopsis thaliana. These compounds are known for their roles in plant defense mechanisms against pests and pathogens. 'Guilt-by-association' (GBA) approach predicts genes encoding proteins with similar function tend to share gene expression pattern generated from high throughput sequencing data. Recent studies have successfully identified GSL genes using GBA approach, followed by targeted verification of gene expression and metabolite data. Therefore, a GSL co-expression network was constructed using known GSL genes obtained from our in-house database, SuCComBase. DPClusO was used to identify subnetworks of the GSL co-expression network followed by Fisher's exact test leading to the discovery of a potential gene that encodes the ARIA-interacting double AP2-domain protein (ADAP) transcription factor (TF). Further functional analysis was performed using an effective gene silencing system known as CRES-T. By applying CRES-T, ADAP TF gene was fused to a plant-specific EAR-motif repressor domain (SRDX), which suppresses the expression of ADAP target genes. In this study, ADAP was proposed as a negative regulator in aliphatic GSL biosynthesis due to the over-expression of downstream aliphatic GSL genes (UGT74C1 and IPMI1) in ADAP-SRDX line. The significant over-expression of ADAP gene in the ADAP-SRDX line also suggests the behavior of the TF that negatively affects the expression of UGT74C1 and IPMI1 via a feedback mechanism in A. thaliana.

Liquiritoside Alleviated Pb Induced Stress in Brassica rapa subsp. Parachinensis: Modulations in Glucosinolate Content and Some Physiochemical Attributes

Current research was conducted to explore the effects of liquiritoside on the growth and physiochemical features of Chinese flowering cabbage (Brassica rapa subsp. parachinensis) under lead (Pb) stress. Lead stressed B. rapa plants exhibited decreased growth parameters, chlorophyll, and carotenoid contents. Moreover, Pb toxicity escalated the synthesis of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), flavonoids, phenolics, and proline in treated plants. Nevertheless, foliar application of liquiritoside mitigated Pb toxicity by decreasing oxidative stress by reducing cysteine, H₂O_2, and MDA contents in applied plants. Liquiritoside significantly increased plant height, shoot fresh weight and dry weight, number of leaves, and marketable value of Chinese flowering cabbage plants exposed to Pb toxicity. This biotic elicitor also enhanced the proline, glutathione, total phenolics, and flavonoid contents in Chinese flowering cabbage plants exposed to Pb stress compared with the control. Additionally, total glucosinolate content, phytochelatins (PCs), and non-protein thiols were effectively increased in plants grown under Pb regimes compared with the control plants. Overall, foliar application of liquiritoside can markedly alleviate Pb stress by restricting Pb translocation in Chinese flowering cabbage.

Genetic transfection, hairy root induction and solasodine accumulation in elicited hairy root clone of Solanum erianthum D. Don

An efficient genetic transfection technique has been established using A4 strain of Agrobacterium rhizogenes for the first time in a medicinally valuable plant Solanum erianthum D. Don. The explants were randomly pricked with sterile needle, inoculated with bacterial suspension. The infected leaves were then washed and transferred to MS basal medium fortified with cefotaxime for hairy root induction. A maximum transformation efficiency of 72 % has been recorded after two days of co-cultivation period. The transfer of rolA and rolB genes from the bacterium to the plant genome has been confirmed in five transformed hairy rootlines by standard Polymerase Chain Reaction technique. On the basis of growth analysis and secondary metabolite study two potential rhizoclones (A4-HR-A and A4-HR-B) were selected. Rhizoclone A4-HR-A can produce highest amount of alkaloid, phenolic and flavonoid, whereas A4-HR-B was observed to be highest tannin producer. Alkaloid like solasodine, commercially important for steroidal drug synthesis, was quantified from leaf and A4-HR-A clone by an improved High Performance Liquid Chromatography method. This showed a sustainable increase (1.33 fold) in production of solasodine in hairy rootline.

Complete chloroplast genome sequence of turnip (Brassica rapa. ssp. rapa): genome structure and phylogenetic analysis

Turnip (Brassica rapa. ssp. rapa) is considered worldwide to be one of the most important leaf and root vegetable crops in the Brassicaceae family. However, to date, few chloroplast (cp) genomic resources have been reported for this genus. Here, we determined the complete cp genome sequences of Brassica rapa ssp. rapa. A 153,621 bp quadripartite cycle without any gap was obtained with a large single-copy region (LSC) of 83,512 bp, a small single-copy region (SSC) of 17,683 bp, and two inverted repeat (IR), IRa and IRb of 26,213 bp. A total of 132 genes were identified, including 87 protein-coding genes (PCG), 37 transfer RNA (tRNA), and 8 ribosomal RNA (rRNA). The phylogenetic analysis of ten other crops selected showed that the turnip was most closely related to the Brassica rapa.

Expression profiles of glucosinolate biosynthetic genes in turnip (Brassica rapa var. rapa) at different developmental stages and effect of transformed flavin-containing monooxygenase genes on hairy root glucosinolate content

BACKGROUND

Glucosinolates (GSLs) are secondary metabolites, mainly existing in Brassica vegetables. Their breakdown products have health benefits and contribute to the distinctive taste of these vegetables. Because of their high value, there is a lot of interest in developing breeding strategies to increase the content of beneficial GSLs in Brassica species. GSLs are synthesized from certain amino acids and their biological roles depend largely on the structure of their side chains. Flavin-containing monooxygenase (FMO_GS-OX ) genes are involved in the synthesis of these side chains. To better understand GSL biosynthesis, we sequenced the transcriptomes of turnip (Brassica rapa var. rapa) tubers at four developmental stages (S1-S4) and determined their GSL content.

RESULTS

The total GSL content was high at the early stage (S1) of tuber development and increased up to S3, then decreased at S4. We detected 61 differentially expressed genes, including five FMO_GS-OX genes, that were related for GSL biosynthesis among the four developmental stages. Most of these genes were highly expressed at stages S1 to S3, but their expression was much lower at S4. We estimated the effect of the five FMO_GS-OX genes on GSL content by overexpressing them in turnip hairy roots and found that the amount of aliphatic GSLs increased significantly in the transgenic plants.

CONCLUSION

The transcriptome data and characterization of genes involved in GSL biosynthesis, particularly the FMO_GS-OX genes, will be valuable for improving the yield of beneficial GSLs in turnip and other Brassica crops. © 2019 Society of Chemical Industry.

Advances in nanomaterials as novel elicitors of pharmacologically active plant specialized metabolites: current status and future outlooks

During the last few decades major advances have shed light on nanotechnology. Nanomaterials have been widely used in various fields such as medicine, energy, cosmetics, electronics, biotechnology and pharmaceuticals. Owing to their unique physicochemical characteristics and nanoscale structures, nanoparticles (NPs) have the capacity to enter into plant cells and interact with intracellular organelles and various metabolites. The effects of NPs on plant growth, development, physiology and biochemistry have been reported, but their impact on plant specialized metabolism (aka as secondary metabolism) still remains obscure. In reaction to environmental stress and elicitors, a common response in plants results in the production or activation of different types of specialized metabolites (e.g., alkaloids, terpenoids, phenolics and flavonoids). These plant specialized metabolites (SMs) are important for plant adaptation to an adverse environment, but also a huge number of them are biologically active and used in various commercially-valued products (pharmacy, cosmetic, agriculture, food/feed). Due to their wide array of applications, SMs have attracted much attention to explore and develop new strategies to enhance their production in plants. In this context, NPs emerged as a novel class of effective elicitors to enhance the production of various plant SMs. In recent years, many reports have been published regarding the elicitation of SMs by different types of NPs. However, in order to achieve an enhanced and sustainable production of these SMs, in-depth studies are required to figure out the most suitable NP in terms of type, size and/or effective concentration, along with a more complete understanding about their uptake, translocation, internalization and elicitation mechanisms. Herein, we are presenting a comprehensive and critical account of the plant SMs elicitation capacities of the three main classes of nanomaterials (i.e., metallic NPs (MNPs), metal oxide NPs (MONPs) and carbon related nanomaterials). Their different proposed uptake, translocation and internalization pathways as well as elicitation mechanism along with their possible deleterious effect on plant SMs and/or phytotoxic effects are summarized. We also identified and critically discussed the current research gaps existing in this field and requiring future investigation to further improve the use of these nanomaterials for an efficient production of plant SMs.

Establishment and optimization of mRNA in situ hybridization system in turnip (Brassica rapa var. rapa)

BACKGROUND

In situ hybridization (ISH) is a general molecular biological technique used to determine the spatiotemporal expression of genes in many species. In the past few years, numerous ISH protocols have been established in many species. Turnip (Brassica rapa var. rapa) is an important crop in the world, especially in the Plateau area of China, and is a traditional Tibetan medicine. However, ISH protocol in turnip has not been established.

RESULTS

We explored and established an optimal workflow for mRNA ISH system for turnip which has been evaluated using BrrCLV3 and BrrWUSa. The optimal methods include: (1) fixation method, (2) protease K pretreatment time, (3) probe length and concentration, (4) washing temperature. We also provide advice on weakening background and improving the efficiency of RNA transcription in vitro. The expression of the BrrCLV3 gene in turnip was detected by the optimized system, and the applicability of the system was confirmed by using BrrWUSa.

CONCLUSIONS

In this study, we established and optimized the mRNA ISH system for turnip. We explored and found that (1) FAA fixative was the optimized fixation method, (2) 30 min was the optimized protease K pretreatment time, (3) 100 bp, 100 ng/ml probe had good hybridization signal, (4) the optimized washing temperature was 52 °C. It provides a powerful method to locate mRNA in the tissue, which can study the expression and function of turnip's genes. As such, it has considerable advantages in terms of time and cost.

Differential Regulation of Anthocyanins in Green and Purple Turnips Revealed by Combined De Novo Transcriptome and Metabolome Analysis

Purple turnip Brassica rapa ssp. rapa is highly appreciated by consumers but the metabolites and molecular mechanisms underlying the root skin pigmentation remain open to study. Herein, we analyzed the anthocyanin composition in purple turnip (PT) and green turnip (GT) at five developmental stages. A total of 21 anthocyanins were detected and classified into the six major anthocynanin aglycones. Distinctly, PT contains 20 times higher levels of anthocyanins than GT, which explain the difference in the root skin pigmentation. We further sequenced the transcriptomes and analyzed the differentially expressed genes between the two turnips. We found that PT essentially diverts dihydroflavonols to the biosynthesis of anthocyanins over flavonols biosynthesis by strongly down-regulating one flavonol synthase gene, while strikingly up-regulating dihydroflavonol 4-reductase (DFR), anthocyanidin synthase and UDP-glucose: flavonoid-3-O-glucosyltransferase genes as compared to GT. Moreover, a nonsense mutation identified in the coding sequence of the DFR gene may lead to a nonfunctional protein, adding another hurdle to the accumulation of anthocyanin in GT. We also uncovered several key members of MYB, bHLH and WRKY families as the putative main drivers of transcriptional changes between the two turnips. Overall, this study provides new tools for modifying anthocyanin content and improving turnip nutritional quality.

Variability of Bioactive Glucosinolates, Isothiocyanates and Enzyme Patterns in Horseradish Hairy Root Cultures Initiated from Different Organs

Horseradish hairy root cultures are suitable plant tissue organs to study the glucosinolate-myrosinase-isothiocyanate system and also to produce the biologically active isothiocyanates and horseradish peroxidase, widely used in molecular biology. Fifty hairy root clones were isolated after Agrobacterium rhizogenes infection of surface sterilized Armoracia rusticana petioles and leaf blades, from which 21 were viable after antibiotic treatment. Biomass properties (e.g. dry weight %, daily growth index), glucosinolate content (analyzed by liquid chromatography-electronspray ionization-mass spectrometry (LC-ESI-MS/MS)), isothiocyanate and nitrile content (analyzed by gas chromatography-mass spectrometry (GC-MS)), myrosinase (on-gel detection) and horseradish peroxidase enzyme patterns (on-gel detection and spectrophotometry), and morphological features were examined with multi-variable statistical analysis. In addition to the several positive and negative correlations, the most outstanding phenomenon was many parameters of the hairy root clones showed dependence on the organ of origin. Among others, the daily growth index, sinigrin, glucobrassicin, 3-phenylpropionitrile, indole-3-acetonitrile and horseradish peroxidase values showed significantly higher levels in horseradish hairy root cultures initiated from leaf blades.

Evaluation of Polyphenolic Compounds and Pharmacological Activities in Hairy Root Cultures of Ligularia fischeri Turcz. f. spiciformis (Nakai)

A considerable amount of bioactive compounds have been used for the biopharmaceutical engineering to help human health and nutrition. Hairy root culture (HRC) or transgenic root is a favourable alternative technique for phytochemical production. Ligularia fischeri is a significant source of pharmaceutically important active compounds with an enormous range of health care applications. HRC of L. fischeri was developed using Agrobacterium rhizogenes for the production of polyphenolic compounds with antioxidant, antimicrobial, antidiabetic, anticancer and anti-inflammatory pharmaceutical activities. Hairy roots (HRs) were selected by morphological assessment, genetic and molecular analyses. The maximum accumulation of fresh mass (94.15 g/L) and dry mass (9.45 g/L) was recorded in MS liquid medium supplemented with 30 g/L sucrose at 28 days. Furthermore, HRs successfully produced numerous polyphenolic compounds, including six hydroxycinnamic acids, seven flavonols, seven hydroxybenzoic acids, vanillin, resveratrol, pyrogallol, homogentisic, and veratric acids, which were identified by UHPLC analysis. HRs produced higher total phenolic (185.65 mg/g), and flavonoid (5.25 mg/g) contents than non-transformed roots (125.55 mg/g and 3.75 mg/g). As a result of these metabolic changes, pharmaceutical activities were found higher in HRs than non-transformed roots (NTRs). The present study indicates that HRC has the potential to increase the content of beneficial polyphenolic compounds with higher potential pharmaceutical activities. To the best of our knowledge, the present study is the first report on enhancing the production of polyphenolic compounds with pharmaceutical activities from the HRCs of L. fischeri.

Elicitation of silver nanoparticles enhanced the secondary metabolites and pharmacological activities in cell suspension cultures of bitter gourd

This study describes the influence of bio-synthesized silver nanoparticles (AgNPs) on phytochemicals and their pharmacological activities in the cell suspension cultures (CSC) of bitter gourd. To standardize the effect of sucrose, plant growth regulators, medium, AgNPs and growth kinetics for the biomass and bioactive compounds accumulation in CSC of bitter gourd. The medium comprising MS salts, sucrose (30 g/L) with 2,4-D (1.0 mg/L) and TDZ (0.1 mg/L) at 28 days of CSC was appropriate for biomass and bioactive compound accumulation. The contents of silver, malondialdehyde and hydrogen peroxide were highly elevated in AgNPs (10 mg/L)-elicited CSC when compared with non-elicited CSC. AgNPs (5 mg/L) elicited CSC extracts had significantly enhanced the production of total phenolic (3.5 ± 0.2 mg/g), and flavonoid (2.5 ± 0.06 mg/g) contents than in the control CSC extracts (2.5 ± 0.1 and 1.6 ± 0.05 mg/g). AgNPs (5 mg/L) elicited CSC showed a higher amount of flavonols (1822.37 µg/g), hydroxybenzoic (1713.40 µg/g) and hydroxycinnamic (1080.10 µg/g) acids than the control CSC (1199, 1394.42 and 944.52 µg/g, respectively). Because of these metabolic changes, the pharmacological activities (antioxidant, antidiabetic, antibacterial, antifungal and anticancer) were high in the AgNPs (5 mg/L)-elicited CSC extracts in bitter gourd. The study suggested the effectiveness of elicitation process in enhancing the accumulation of phenolic compounds and pharmacological activities. AgNPs-elicited CSC offered an effective and favorable in vitro method to improve the production of bioactive compounds for potential uses in pharmaceutical industries.

In vitro plant tissue culture: means for production of biological active compounds

MAIN CONCLUSION

Plant tissue culture as an important tool for the continuous production of active compounds including secondary metabolites and engineered molecules. Novel methods (gene editing, abiotic stress) can improve the technique. Humans have a long history of reliance on plants for a supply of food, shelter and, most importantly, medicine. Current-day pharmaceuticals are typically based on plant-derived metabolites, with new products being discovered constantly. Nevertheless, the consistent and uniform supply of plant pharmaceuticals has often been compromised. One alternative for the production of important plant active compounds is in vitro plant tissue culture, as it assures independence from geographical conditions by eliminating the need to rely on wild plants. Plant transformation also allows the further use of plants for the production of engineered compounds, such as vaccines and multiple pharmaceuticals. This review summarizes the important bioactive compounds currently produced by plant tissue culture and the fundamental methods and plants employed for their production.

Elite hairy roots of Raphanus sativus (L.) as a source of antioxidants and flavonoids

An efficient protocol for hairy root induction in radish was established by optimizing several parameters that affect the efficiency of Agrobacterium rhizogenes-mediated transformations. Explants wounded using sterile hypodermic needle, infected with Agrobacterium suspension (0.6 OD600) for 10 min and co-cultivated in 1/2 MS medium containing acetosyringone (100 µM) for 2 days displayed maximum percentage of hairy root induction using MTCC 2364 (77.6%) and MTCC 532 (67.6%). On further experiments with MTCC 2364 initiated hairy roots, maximum biomass accumulation (fresh weight = 9.50 g; dry weight = 1.48 g) was achieved in liquid 1/2 MS medium supplemented with 87.6 mM sucrose after 40 days of culture. Transgenic state of hairy roots of MTCC 2364 was confirmed by polymerase chain reaction using rolB- and rolC-specific primers. The MTCC 2364-induced hairy roots produced higher amount of phenolic (33.0 mg g-1), flavonoid (48.0 mg g-1), and quercetin (114.8 mg g-1) content compared to auxin-induced roots of non-transformed radish. Furthermore, the results of ferric reducing antioxidant power and 1,1-diphenyl-2-picrylhydrazyl assay confirmed that the antioxidant activity of MTCC 2364 root extracts was improved when compared to auxin-induced roots of non-transformed radish. The present study offers a new insight in radish for production of phenolics and flavonoids (quercetin) using A. rhizogenes-mediated hairy root induction.

Bioactive Compounds in Brassicaceae Vegetables with a Role in the Prevention of Chronic Diseases

The beneficial role of the Mediterranean diet in the prevention of chronic diseases, including cardiovascular diseases, diabetes, and obesity, is well-recognized. In this context, Brassicaceae are considered important vegetables due to several evidences of their health promoting effects that are associated to bioactive compounds present in the edible parts of the plants. In this review, the mechanisms of action and the factors regulating the levels of the bioactive compounds in Brassicaceae have been discussed. In addition, the impact of industrial and domestic processing on the amount of these compounds have been considered, in order to identify the best conditions that are able to preserve the functional properties of the Brassicaceae products before consumption. Finally, the main strategies used to increase the content of health-promoting metabolites in Brassica plants through biofortification have been analyzed.

Genetic Transformation and Hairy Root Induction Enhance the Antioxidant Potential of Lactuca serriola L

Lactuca serriola L. is a herbaceous species, used for human nutrition and medicinal purposes. The high antioxidant capacity of L. serriola indicates the possibility of enhancing its edible and health potential by increasing the flavonoid and phenolic contents. The present study aimed at enhancing the production of phenolics and flavonoids by hairy root cultures in Lactuca serriola transformed with Agrobacterium rhizogenes strain AR15834 harbouring the rolB gene. The genetic transformation of rolB in transformed roots was validated, and rolB expression level was evaluated using real-time qPCR analysis. Expression levels of flavonoid biosynthesis genes (CHI, PAL, FLS, and CHS) were assessed in the hairy and nontransformed roots. Results showed higher expression levels in the transgenic roots than in the nontransformed ones (p < 0.01). Transgenic hairy roots exhibited a 54.8-96.7% increase in the total phenolic content, 38.1-76.2% increase in the total flavonoid content, and 56.7-96.7% increase in the total reducing power when compared with the nontransgenic roots (p < 0.01). DPPH results also revealed that the transgenic hairy roots exhibited a 31.6-50% increase in antioxidant potential, when compared to normal roots. This study addressed the enhancement of secondary metabolite biosynthesis by hairy root induction in L. serriola.

Biosynthesis and bioactivity of glucosinolates and their production in plant in vitro cultures

Glucosinolates are biologically active compounds which are involved in plant defense reaction. The use of plant in vitro cultures and genetic engineering is a promising strategy for their sustainable production. Glucosinolates are a class of secondary metabolites found mainly in Brassicaceae, which contain nitrogen and sulfur in their structures. Glucosinolates are divided into three groups depending on the amino acid from which they are biosynthesized. Aliphatic glucosinolates are generally derived from leucine, valine, methionine, isoleucine and alanine while indole and aromatic glucosinolates are derived from tryptophan and phenylalanine or tyrosine, respectively. These compounds are hydrolyzed by the enzyme myrosinase when plants are stressed by biotic and abiotic factors, obtaining different degradation products. Glucosinolates and their hydrolysis products play an important role in plant defense responses against different types of stresses. In addition, these compounds have beneficial effect on human health because they are strong antioxidants and they have potent cardiovascular, antidiabetic, antimicrobial and antitumoral activities. Due to all the properties described above, the demand for glucosinolates and their hydrolysis products has enormously increased, and therefore, new strategies that allow the production of these compounds to be improved are needed. The use of plant in vitro cultures is emerging as a biotechnological strategy to obtain glucosinolates and their derivatives. This work is focused on the biosynthesis of glucosinolates and the bioactivity of these compounds in plants. In addition, a detailed study on the strategies used to increase the production of several glucosinolates, in particular those synthesized in Brassicaceae, using in vitro plant cultures has been made. Special attention has been paid for increasing the production of glucosinolates and their derivatives using metabolic engineering.