Engineering high yields of secondary metabolites in Rubia cell cultures through transformation with rol genes

Activation of anthraquinone biosynthesis in long-cultured callus culture of Rubia cordifolia transformed with the rolA plant oncogene

The RolA protein belongs to the RolB class of plant T-DNA oncogenes, and shares structural similarity with the papilloma virus E2 DNA-binding domain. It has potentially as an inducer of plant secondary metabolism, although its role in biotechnology has yet to be realised. In this investigation, a Rubia cordifolia callus culture transformed with the rolA plant oncogene for more than 10 years was analysed. Expression of the rolA gene in the callus line was stable during long-term cultivation, and growth parameters were both elevated and stable, exceeding those of the non-transformed control culture. The rolA-transformed calli not only demonstrated remarkably stable growth, but also the ability to increase the yield of anthraquinones (AQs) in long-term cultivation. After ten years of cultivating rolA callus lines, we observed an activation of AQ biosynthesis from 200 mg/l to 874 mg/l. The increase was mainly due to activation of ruberitrinic acid biosynthesis. The expression of key AQ biosynthesis genes was strongly activated in rolA-transgenic calli. We compared the effects of the rolA gene with those of the rolB gene, which was previously considered the most potent inducer of secondary metabolism, and showed that rolA was more productive under conditions of long-term cultivation.

Tempo-Spatial Pattern of Stepharine Accumulation in Stephania Glabra Morphogenic Tissues

Alkaloids attract great attention due to their valuable therapeutic properties. Stepharine, an aporphine alkaloid of Stephania glabra plants, exhibits anti-aging, anti-hypertensive, and anti-viral effects. The distribution of aporphine alkaloids in cell cultures, as well as whole plants is unknown, which hampers the development of bioengineering strategies toward enhancing their production. The spatial distribution of stepharine in cell culture models, plantlets, and mature micropropagated plants was investigated at the cellular and organ levels. Stepharine biosynthesis was found to be highly spatially and temporally regulated during plant development. We proposed that self-intoxication is the most likely reason for the failure of the induction of alkaloid biosynthesis in cell cultures. During somatic embryo development, the toxic load of alkaloids inside the cells increased. Only specialized cell sites such as vascular tissues with companion cells (VT cells), laticifers, and parenchymal cells with inclusions (PI cells) can tolerate the accumulation of alkaloids, and thus circumvent this restriction. S. glabra plants have adapted to toxic pressure by forming an additional transport secretory (laticifer) system and depository PI cells. Postembryonic growth restricts specialized cell site formation during organ development. Future bioengineering strategies should include cultures enriched in the specific cells identified in this study.

Increase in isoflavonoid content in Glycine max cells transformed by the constitutively active Ca2+ independent form of the AtCPK1 gene

Calcium-dependent protein kinases (CDPKs) represent a class within a multigene family that plays an important role in biotic and abiotic plant stress responses and is involved in the regulation of secondary metabolite biosynthesis. Our previous study showed that overexpression of the mutant constitutively active Ca2+ independent form of the AtCPK1 gene (AtCPK1-Ca) significantly increased the biosynthesis of anthraquinones and stilbenes in Rubia cordifolia L. and Vitis amurensis Rupr. transgenic cell cultures, respectively. Here, we have established transgenic calli of soybean plants Glycine max (L.) Merr. that express the AtCPK1-Ca gene. Heterologous expression of the AtCPK1-Ca gene provoked a 5.2-fold increase in total isoflavone production up to 208.09 mg/L, along with an increase in isoflavone aglycones production up to 6.60 mg/L, which is 3-fold greater than that of the control culture. The production of prenylated isoflavones significantly increased, reaching 3.78 mg/L, 13-fold higher than in the control culture. The expression levels of 4-coumarate:CoA ligases, isoflavone synthases, 2-hydroxyisoflavanone dehydratase, isoflavone dimethylallyltransferase, and coumestrol 4-dimethylallyltransferase genes in transgenic cell cultures significantly increased. Thus, heterologous expression of the AtCPK1-Ca gene can be used to bioengineer plant cell cultures that produce isoflavonoids.

Natural products against Alzheimer's disease: Pharmaco-therapeutics and biotechnological interventions

Alzheimer's disease (AD) is a severe, chronic and progressive neurodegenerative disease associated with memory and cognition impairment ultimately leading to death. It is the commonest reason of dementia in elderly populations mostly affecting beyond the age of 65. The pathogenesis is indicated by accumulation of the amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFT) in brain tissues and hyperphosphorylation of tau protein in neurons. The main cause is considered to be the formation of reactive oxygen species (ROS) due to oxidative stress. The current treatment provides only symptomatic relief by offering temporary palliative therapy which declines the rate of cognitive impairment associated with AD. Inhibition of the enzyme acetylcholinesterase (AChE) is considered as one of the major therapeutic strategies offering only symptomatic relief and moderate disease-modifying effect. Other non-cholinergic therapeutic approaches include antioxidant and vitamin therapy, stem cell therapy, hormonal therapy, use of antihypertensive or lipid-lowering medications and selective phosphodiesterase (PDE) inhibitors, inhibition of β-secretase and γ-secretase and Aβ aggregation, inhibition of tau hyperphosphorylation and intracellular NFT, use of nonsteroidal anti-inflammatory drugs (NSAIDs), transition metal chelators, insulin resistance drugs, etanercept, brain-derived neurotrophic factor (BDNF) etc. Medicinal plants have been reported for possible anti-AD activity in a number of preclinical and clinical trials. Ethnobotany, being popular in China and in the Far East and possibly less emphasized in Europe, plays a substantial role in the discovery of anti-AD agents from botanicals. Chinese Material Medica (CMM) involving Chinese medicinal plants has been used traditionally in China in the treatment of AD. Ayurveda has already provided numerous lead compounds in drug discovery and many of these are also undergoing clinical investigations. A number of medicinal plants either in their crude forms or as isolated compounds have exhibited to reduce the pathological features associated with AD. In this present review, an attempt has been made to elucidate the molecular mode of action of various plant extracts, phytochemicals and traditional herbal formulations investigated against AD as reported in various preclinical and clinical tests. Herbal synergism often found in polyherbal formulations were found effective to combat disease heterogeneity as found in complex pathogenesis of AD. Finally a note has been added to describe biotechnological improvement, genetic and genomic resources and mathematical and statistical techniques for empirical model building associated with anti-AD plant secondary metabolites and their source botanicals.

The rolC gene increases caffeoylquinic acid production in transformed artichoke cells

Caffeoylquinic acids are found in artichokes, and they are currently considered important therapeutic or preventive agents for treating Alzheimer's disease and diabetes. We transformed artichoke [the cultivated cardoon or Cynara cardunculus var. altilis DC (Asteraceae)] with the rolC gene, which is a known inducer of secondary metabolism. High-performance liquid chromatography with UV and high-resolution mass spectrometry (HPLC-UV-HRMS) revealed that the predominant metabolites synthesized in the transgenic calli were 1,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, and chlorogenic acid. The rolC-transformed calli contained 1.5% caffeoylquinic acids by dry weight. The overall production of these metabolites was three times higher than that of the corresponding control calli. The enhancing effect of rolC remained stable over long-term cultivation.

Polyphenolic Compounds from Callus Cultures of Iris Pseudacorus

A callus culture of Iris pseudacorus L. (Iridaceae) was established from plant leaves using a modified Murashige and Skoog medium. A derivative of cinnamic acid (lavandoside) (1), a neolignan (dehydrodiconiferyl alcohol-4- O-β-D-glucopyranoside) (2) as well as three isoflavonoids, tectoridin (3), tectorigenin (4), and iristectorigenin A (5) were isolated from the callus culture. Under normal conditions, the calli accumulated 0.4% DW of polyphenols. The addition of phenylalanine to a concentration of 1 mM resulted in a 1.5-fold increase in isoflavonoid production, allowing the accumulation of 0.69% of polyphenols in the callus dry weight. Tectorigenin, a promising chemotherapeutic and chemopreventive agent for the treatment of carcinomas, was produced in I. pseudacorus calli in high quantities (0.3% DW).

Recent advances in the understanding of Agrobacterium rhizogenes-derived genes and their effects on stress resistance and plant metabolism

It is commonly accepted that the plant pathogens Agrobacterium rhizogenes and Agrobacterium tumefaciens, acting via their T-DNA oncogenes, disturb hormone metabolism or hormone perception pathways in plants, thereby attaining their aim of successful pathogenesis. In this work, we summarize recent data on the A. rhizogenes rolC and rolB oncogenes in comparison to the A. tumefaciens 6b oncogene with respect to their effects on the physiology of transformed cells. The newly discovered functions of the rol genes include the modulation of secondary metabolism, the modulation of levels of intracellular ROS and stress resistance of transformed cells, changed sucrose metabolism, and the inhibition of programmed cell death. We show that the rol genes do not have suppressive effects on plant innate immunity; rather, these genes activate plant defense reactions. The existence of not only the hormone-related mechanism of pathogenicity but also the defense-related mechanism of pathogenicity during plant-Agrobacterium interactions is suggested.

Rosmarinic acid and its derivatives: biotechnology and applications

Rosmarinic acid (RA) is one of the first secondary metabolites produced in plant cell cultures in extremely high yields, up to 19% of the cell dry weight. More complex derivatives of RA, such as rabdosiin and lithospermic acid B, later were also obtained in cell cultures at high yields. RA and its derivatives possess promising biological activities, such as improvement of cognitive performance, prevention of the development of Alzheimer's disease, cardioprotective effects, reduction of the severity of kidney diseases and cancer chemoprevention. The TNF-α-induced NF-κB signaling pathway has emerged as a central target for RA. Despite these impressive activities and high yields, the biotechnological production of these metabolites on an industrial scale has not progressed. We summarized data suggesting that external stimuli, the Ca(2+)-dependent NADPH oxidase pathway and processes of protein phosphorylation/dephosphorylation are involved in the regulation of biosynthesis of these substances in cultured plant cells. In spite of growing information about pathways regulating biosynthesis of RA and its derivatives in cultured plant cells, the exact mechanism of regulation remains unknown. We suggest that further progress in the biotechnology of RA and its derivatives can be achieved by using new high-throughput techniques.

Molecular cloning and characterization of seven class III peroxidases induced by overexpression of the agrobacterial rolB gene in Rubia cordifolia transgenic callus cultures

Here, seven new class III peroxidase genes of Rubia cordifolia L., RcPrx01-RcPrx07, were isolated and characterized. Expression of the Prx genes was studied in R. cordifolia aerial organs as well as in cells transformed with the rolB and rolC genes of Agrobacterium rhizogenes and cells transformed with the wild-type A. rhizogenes A4 strain. In rolC- and rolB-transformed cells, the rol genes were expressed under the control of the 35S promoter, whereas in A. rhizogenes A4-transformed cells the rol genes were expressed under the control of their native promoters. All studied peroxidase genes were greatly upregulated in rolB-overexpressing cells. In contrast, overexpression of the rolC gene and expression of the rol genes under the control of their native promoters had little effect on the abundance of peroxidase transcripts. In accordance with this observation, peroxidase activity was substantially increased in rolB cells and was slightly affected in other transformed cells. Our results indicate that rolB strictly affects the regulation of a set of seven R. cordifolia class III peroxidases.

The rolB gene suppresses reactive oxygen species in transformed plant cells through the sustained activation of antioxidant defense

The rolB (for rooting locus of Agrobacterium rhizogenes) oncogene has previously been identified as a key player in the formation of hairy roots during the plant-A. rhizogenes interaction. In this study, using single-cell assays based on confocal microscopy, we demonstrated reduced levels of reactive oxygen species (ROS) in rolB-expressing Rubia cordifolia, Panax ginseng, and Arabidopsis (Arabidopsis thaliana) cells. The expression of rolB was sufficient to inhibit excessive elevations of ROS induced by paraquat, menadione, and light stress and prevent cell death induced by chronic oxidative stress. In rolB-expressing cells, we detected the enhanced expression of antioxidant genes encoding cytosolic ascorbate peroxidase, catalase, and superoxide dismutase. We conclude that, similar to pathogenic determinants in other pathogenic bacteria, rolB suppresses ROS and plays a role not only in cell differentiation but also in ROS metabolism.

Catechin production in cultured cells of Taxus cuspidata and Taxus baccata

The main polyphenols in callus and cell suspension cultures of Taxus cuspidata and T. baccata were (+)-catechin and (-)-epicatechin, while lignans, such as (+)-taxiresinol, (+)-isotaxiresinol, (+)-isolariciresinol and (-)-secoisolariciresinol, were present in trace amounts. T. cuspidata cells contained 1.7% (+)-catechin and 2.4% (-)-epicatechin on dry wt basis but when stimulated with methyl jasmonate produced 3.4% catechin and 5.2% epicatechin. These are the highest levels of these metabolites obtained in plant cell cultures.