New Routes to Plant Secondary Products

Enhancement of Phytosterol and Triterpenoid Production in Plant Hairy Root Cultures-Simultaneous Stimulation or Competition?

Plant in vitro cultures, including hairy roots, can be applied for controlled production of valuable natural products, such as triterpenoids and sterols. These compounds originate from the common precursor squalene. Sterols and triterpenoids distinctly differ in their functions, and the 2,3-oxidosqualene cyclization step is often regarded as a branch point between primary and secondary (more aptly: general and specialized) metabolism. Considering the crucial role of phytosterols as membrane constituents, it has been postulated that unconstrained biosynthesis of triterpenoids can occur when sterol formation is already satisfied, and these compounds are no longer needed for cell growth and division. This hypothesis seems to follow directly the growth-defense trade-off plant dilemma. In this review, we present some examples illustrating the specific interplay between the two divergent pathways for sterol and triterpenoid biosynthesis appearing in root cultures. These studies were significant for revealing the steps of the biosynthetic pathway, understanding the role of particular enzymes, and discovering the possibility of gene regulation. Currently, hairy roots of many plant species can be considered not only as an efficient tool for production of phytochemicals, but also as suitable experimental models for investigations on regulatory mechanisms of plant metabolism.

Establishment and elicitation of transgenic root culture of Plantago lanceolata and evaluation of its anti-bacterial and cytotoxicity activity

Hairy root induction in Plantago lanceolata was optimized to take advantage of transformed root cultures. The highest frequency of transformation was achieved using leaf explant, A4 strain, pre-cultivation of explant, 150 µM Acetosyringone, 5 min inoculation, half-strength Murashige and Skoog basal medium as co-cultivation, and half-strength Gamborg's basal medium as a selective medium with 3% sucrose. Among the studied compound encompassing gallic acid, catalpol and apigenin, only the production of gallic acid in hairy roots was affected by 20 mg L^-1 AgNO₃ and 100 mg L^-1 chitosan at 24 hr which yielded 7.63, 4.76-fold increase in its content, respectively. The methanolic extracts of hairy roots elicited by 20 mg L^-1 AgNO₃ exhibited anti-bacterial activity (MIC and MBC = 25 mg mL^-1) against Klebsiella pneumoniae, Proteus vulgaris and Salmonella typhi and anti-bacterial potential of non-elicited hairy roots of P. lanceolata (MIC = 25 mg mL^-1 and MBC = 35 mg mL^-1) were more active against Klebsiella pneumoniae and P. vulgaris than other bacteria. The methanolic extracts of the P. lanceolata hairy roots demonstrated significant cytotoxic activity on colorectal carcinoma cell line (SW-480) with IC₅₀ = 250.65 ± 6.8 µg mL^-1 in comparison to human embryonic kidney (HEK-293) with IC₅₀ = 5263.65 ± 4.6 µg mL^-1. Plantago lanceolata hairy roots showed important biological activity explaining its role in traditional medicine.

Agrobacterium-Mediated Transformation in the Evolution of Plants

In most cases, the genetic engineering of plants uses Agrobacterium-mediated transformation to introduce novel genes. In nature, insertion of T-DNA into the plant genome and its subsequent transfer via sexual reproduction have been shown for several species in the genera Nicotiana, Ipomoea , and Linaria . A sequence homologous to T-DNA of the Ri plasmid of Agrobacterium rhizogenes was found in the genome of wild-type Nicotiana glauca (section Noctiflorae) more than 30 years ago and was named "cellular T-DNA" (cT-DNA). It comprises an imperfect inverted repeat and contains homologs of several T-DNA oncogenes (NgrolB, NgrolC, Ngorf13, Ngorf14) and an opine synthesis gene (Ngmis). Multiple cT-DNAs have also been found in species of the sections Tomentosae and Nicotiana of the genus Nicotiana. These ancient cT-DNA genes are still expressed, indicating that they may play a role in the evolution of these plants. In 2012-2013, cT-DNA was detected and characterized in Linaria vulgaris and L. genistifolia ssp. dalmatica. Their cT-DNA is present in two copies and organized as an imperfect direct tandem repeat, containing LvORF2, LvORF3, LvORF8, LvrolA, LvrolB, LvrolC, LvORF13, LvORF14, and the Lvmis genes. In 2015, cT-DNA was found in Ipomoea. Two types of T-DNA-like sequences were described within this genera, and their distribution varied among cultured hexaploid, tetraploid, and wild diploid forms. Thus, several independent T-DNA integration events occurred in the genomes of these three plant genera. We propose that the events of T-DNA insertion in the plant genome might have affected their evolution, resulting in the creation of new plant species. In this chapter, we focus on the structure and functions of cT-DNA in Linaria, Nicotiana, and Ipomoea and discuss their possible evolutionary role.

Efficient Rutin and Quercetin Biosynthesis through Flavonoids-Related Gene Expression in Fagopyrum tataricum Gaertn. Hairy Root Cultures with UV-B Irradiation

Transformed hairy roots had been efficiently induced from the seedlings of Fagopyrum tataricum Gaertn. due to the infection of Agrobacterium rhizogenes. Hairy roots were able to display active elongation with high root branching in 1/2 MS medium without growth regulators. The stable introduction of rolB and aux1 genes of A. rhizogenes WT strain 15834 into F. tataricum plants was confirmed by PCR analysis. Besides, the absence of virD gene confirmed hairy root was bacteria-free. After six different media and different sources of concentration were tested, the culturing of TB7 hairy root line in 1/2 MS liquid medium supplemented with 30 g l(-1) sucrose for 20 days resulted in a maximal biomass accumulation (13.5 g l(-1) fresh weight, 1.78 g l(-1) dry weight) and rutin content (0.85 mg g(-1)). The suspension culture of hairy roots led to a 45-fold biomass increase and a 4.11-fold rutin content increase in comparison with the suspension culture of non-transformed roots. The transformation frequency was enhanced through preculturing for 2 days followed by infection for 20 min. The UV-B stress treatment of hairy roots resulted in a striking increase of rutin and quercetin production. Furthermore, the hairy root lines of TB3, TB7, and TB28 were chosen to study the specific effects of UV-B on flavonoid accumulation and flavonoid biosynthetic gene expression by qRT-PCR. This study has demonstrated that the UV-B radiation was an effective elicitor that dramatically changed in the transcript abundance of ftpAL, FtCHI, FtCHS, FtF3H, and FtFLS-1 in F. tataricum hairy roots.

Redirection of metabolite biosynthesis from hydroxybenzoates to volatile terpenoids in green hairy roots of Daucus carota

A metabolic shift in green hairy root cultures of carrot from phenylpropanoid/benzenoid biosynthesis toward volatile isoprenoids was observed when compared with the metabolite profile of normal hairy root cultures. Hairy roots cultures of Daucus carota turned green under continuous illumination, while the content of the major phenolic compound p-hydroxybenzoic acid (p-HBA) was reduced to half as compared to normal hairy roots cultured in darkness. p-Hydroxybenzaldehyde dehydrogenase (HBD) activity was suppressed in the green hairy roots. However, comparative volatile analysis of 14-day-old green hairy roots revealed higher monoterpene and sesquiterpene contents than found in normal hairy roots. Methyl salicylate content was higher in normal hairy roots than in green ones. Application of clomazone, an inhibitor of 1-deoxy-D-xylulose 5-phosphate synthase (DXS), reduced the amount of total monoterpenes and sesquiterpenes in green hairy roots compared to normal hairy roots. However, methyl salicylate content was enhanced in both green and normal hairy roots treated with clomazone as compared to their respective controls. Because methyl-erythritol 4-phosphate (MEP) and phenylpropanoid pathways, respectively, contribute to the formation of monoterpenes and phenolic acids biosynthesis, the activities of enzymes regulating those pathways were measured in terms of their in vitro activities, in both green and normal hairy root cultures. These key enzymes were 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), an early regulatory enzyme of the MEP pathway, pyruvate kinase (PK), an enzyme of primary metabolism related to the MEP pathway, shikimate dehydrogenase (SKDH) which is involved in biosynthesis of aromatic amino acids, and phenylalanine ammonia-lyase (PAL) that catalyzes the first step of phenylpropanoid biosynthesis. Activities of DXR and PK were higher in green hairy roots as compared to normal ones, whereas the opposite trend was observed for SKDH and PAL activities. Gene expression analysis of DXR and PAL showed trends similar to those for the respective enzyme activities. Based on these observations, we suggest a possible redirection of metabolites from the primary metabolism toward isoprenoid biosynthesis, limiting the phenolic biosynthetic pathway in green hairy roots grown under continuous light.

Production of anthraquinones, phenolic compounds and biological activities from hairy root cultures of Polygonum multiflorum Thunb

Polygonum multiflorum Thunb. is a highly important medicinal plant producing anthraquinones (emodin and physcion) and phenolic compounds which has pharmaceutical use. In vitro seedling explants such as roots, internodals, nodals and leaves were inoculated with A. rhizogenes strain KCTC 2703. Transformed roots were induced from internodals and leaf explants. Six transgenic clones of hairy roots were established and confirmed by polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR) using rolC specific primers. Hairy roots cultured using MS liquid medium supplemented with 30 g/l sucrose showed highest accumulation of biomass (99.05 g/l FW [fresh weight] and 10.95 g/l DW [dry weight]) and highest production of anthraquinones content (emodin 211.32 μg/g DW and physcion 353.23 μg/g DW) were observed at 20 days. Nearly 9.5-fold increment of biomass was evident in suspension cultures at 20 days of culture and hairy root biomass produced in suspension cultures possessed 3.7- and 3.5-fold higher content of emodin and physcion, respectively, when compared with the untransformed control roots. MS basal liquid medium was superior for the growth of hairy roots and production of anthraquinones compared with other culture media evaluated (SH, B5 and N6), with MS-basal liquid medium supplemented with 30 g/l sucrose was optimal for secondary metabolite production. A total of 23 polyphenolic compounds were identified and quantified from P. multiflorum untransformed and hairy roots, which includes hydroxybenzoic acids, hydroxycinnamic acids, flavonols and other groups of phenolic compounds. The ultra-performance liquid chromatography (UPLC) analysis of the phenolic compounds profile revealed that pyrogallol, hesperidin, naringenin and formononetin were higher in hairy roots compared to untransformed roots. The total phenolics, flavonoids content, antioxidant and antimicrobial activity was high in hairy roots compared to untransformed roots. This is the first report for the production of anthraquinones (emodin and physcion), phenolic compounds and biological activities from hairy root cultures of P. multiflorum.

Metabolomic analysis and phenylpropanoid biosynthesis in hairy root culture of tartary buckwheat cultivars

Buckwheat, Fagopyrum tataricum Gaertn., is an important medicinal plant, which contains several phenolic compounds, including one of the highest content of rutin, a phenolic compound with anti-inflammatory properties. An experiment was conducted to investigate the level of expression of various genes in the phenylpropanoid biosynthetic pathway to analyze in vitro production of anthocyanin and phenolic compounds from hairy root cultures derived from 2 cultivars of tartary buckwheat (Hokkai T8 and T10). A total of 47 metabolites were identified by gas chromatography–time-of-flight mass spectrometry (GC-TOFMS) and subjected to principal component analysis (PCA) in order to fully distinguish between Hokkai T8 and T10 hairy roots. The expression levels of phenylpropanoid biosynthetic pathway genes, through qRT-PCR, showed higher expression for almost all the genes in T10 than T8 hairy root except for FtF3’H-2 and FtFLS-2. Rutin, quercetin, gallic acid, caffeic acid, ferulic acid, 4-hydroxybenzoic acid, and 2 anthocyanin compounds were identified in Hokkai T8 and T10 hairy roots. The concentration of rutin and anthocyanin in Hokkai T10 hairy roots of tartary buckwheat was several-fold higher compared with that obtained from Hokkai T8 hairy root. This study provides useful information on the molecular and physiological dynamic processes that are correlated with phenylpropanoid biosynthetic gene expression and phenolic compound content in F. tataricum species.

Phenolic compound production by different morphological phenotypes in hairy root cultures of Fagopyrum tataricum Gaertn

Hairy roots were obtained after inoculating sterile young stems of Fagopyrum tataricum with Agrobacterium rhizogenes R1000. The established roots displayed two morphological phenotypes when cultured on hormone-free medium containing Murashige-Skoog salts and vitamins. The thin phenotype had a higher growth rate than the thick phenotype. Further, the phenolic compound content of the thin phenotype was higher than that of the thick phenotype. In terms of their total dry weight, the thin phenotype produced an almost double amount of (-)-epigallocatechin as well as more than 51.5% caffeic acid, 65% chlorogenic acid, and 40% rutin compared to the thick phenotype after 21 days of culture. Therefore, selection of the optimal morphological phenotype of hairy roots of tartary buckwheat is an important factor for improved phenolic compound production.

E-p-methoxycinnamic acid production in hairy root cultures of Scrophularia buergeriana Miquel

E-p-methoxycinnamic acid (MCA) is one of the main active constituents of Scrophularia buergeriana Miquel and has hepatoprotective, anti-amnestic, and neuroprotective activities. For studying in vitro production of MCA, we established a hairy root culture of S. buergeriana by infecting leaf explants with Agrobacterium rhizogenes R1000, and tested the growth and MCA production of these cultures using different strengths of media and concentrations of auxins. Hairy roots grown in half-strength MS medium showed the highest levels of growth (10.3 g/l) as well as MCA production (0.83 mg/100 g dry weight). Hairy root culture with the treatment of 0.5 mg/l IBA produced the highest amount of dry weight (11.8 g/l) and MCA (1.26 mg/100 g dry weight) production. These results demonstrate that the hairy root culture of S. buergeriana is a valuable alternative approach for the production of MCA. .

Synthesis of 4-, 5-, 6-, and 7-Azidotryptamines

Synthesis of azidotryptamines from commercially available nitroindoles via the corresponding amino tryptamines in good overall yields (15%-38%) is presented.

Accumulation of p-hydroxybenzoic acid in hairy roots of Daucus carota

We report here the accumulation of p-hydroxybenzoic acid in Agrobacterium rhizogenes-induced hairy root cultures of Daucus carota. This phenolic acid finds application in food, pharmaceutical and polymer industries. Metabolic profiling of phenolics by HPLC/ESI-MS from these hairy roots showed a considerable amount of p-hydroxybenzoic acid accumulation both in cytosol and in the cell wall. Analyses of HCl and NaOH treated soluble phenolic fractions resulted in the elution of peaks with same retention time and similar UV-absorption spectra as observed with p-hydroxybenzoic acid standard. This suggests that p-hydroxybenzoic acid is present in the cytosol as free-form (unconjugated). A correlation has been drawn between the accumulation of soluble and wall-bound phenolic acids on a time-course basis. An apparent absence of any p-hydroxybenzoic acid-glucoside supports this observation, which in turn encourages the idea of its incorporation in the cell wall in an alkaline-labile form.

Overexpression of the Saussurea medusa chalcone isomerase gene in S. involucrata hairy root cultures enhances their biosynthesis of apigenin

Saussurea involucrata is a medicinal plant well known for its flavonoids, including apigenin, which has been shown to significantly inhibit tumorigenesis. Since naturally occurring apigenin is in very low abundance, we took a transgenic approach to increase apigenin production by engineering the flavonoid pathway. A construct was made to contain the complete cDNA sequence of the Saussurea medusa chalcone isomerase (CHI) gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Using an Agrobacterium rhizogenes-mediated transformation system, the chi overexpression cassette was incorporated into the genome of S. involucrata, and transgenic hairy root lines were established. CHI converts naringenin chalcone into naringenin that is the precursor of apigenin. We observed that transgenic hairy root lines grew faster and produced higher levels of apigenin and total flavonoids than wild-type hairy roots did. Over a culture period of 5 weeks, the best-performing line (C46) accumulated 32.1 mgL(-1) apigenin and 647.8 mgL(-1) total flavonoids, or 12 and 4 times, respectively, higher than wild-type hairy roots did. The enhanced productivity corresponded to elevated CHI activity, confirming the key role that CHI played for total flavonoids and apigenin synthesis and the efficiency of the current metabolic engineering strategy.

Plant cell cultures: Chemical factories of secondary metabolites

This review deals with the production of high-value secondary metabolites including pharmaceuticals and food additives through plant cell cultures, shoot cultures, root cultures and transgenic roots obtained through biotechnological means. Plant cell and transgenic hairy root cultures are promising potential alternative sources for the production of high-value secondary metabolites of industrial importance. Recent developments in transgenic research have opened up the possibility of the metabolic engineering of biosynthetic pathways to produce high-value secondary metabolites. The production of the pungent food additive capsaicin, the natural colour anthocyanin and the natural flavour vanillin is described in detail.

Culture of red beet hairy roots by considering variation in sensitivity of tip meristems to hydraulic stress

In the culture of red beet hairy roots in shaking flasks, a period for acclimation without lateral root generation existed at the early stage, and the root tip meristems containing growing points (GPs) were found to be damaged under an elevated shear stress condition. The loading experiments of shear stress to the hairy roots revealed that the GPs subjected to the acclimation acquired tolerance to shear stress, retaining relatively high viability of GPs up to 0.6N/m(2) of loaded shear stress. Next, the hairy roots after culture for 50h at 0.05N/m(2) of shear stress were exposed to conditions at various levels of shear stress in a single column reactor, and a relatively high growth rate was obtained in the vicinity of 1.0N/m(2) of shear stress. According to these results, two-stage cultures of hairy roots were then performed, which was comprised of a first stage for 50h at 0.05N/m(2) of shear stress for the prevention of decay of the GPs caused by hydraulic stress and a second stage for 110h at 1.0N/m(2) of shear stress for active elongation of the GPs with sufficient nutrient supply by regulation of the medium flow rate. The cell concentration ultimately reached 7.6kg dry cells/m(3), although no growth was observed in the case where the hairy roots did not undergo the first stage.

Transgenic hairy roots

Agrobacterium rhizogenes causes hairy root disease in plants. The neoplastic roots produced by A. rhizogenes infection is characterized by high growth rate and genetic stability. These genetically transformed root cultures can produce higher levels of secondary metabolites or amounts comparable to that of intact plants. Hairy root cultures offer promise for production of valuable secondary metabolites in many plants. The main constraint for commercial exploitation of hairy root cultures is their scaling up, as there is a need for developing a specially designed bioreactor that permits the growth of interconnected tissues unevenly distributed throughout the vessel. Rheological characteristics of heterogeneous system should also be taken into consideration during mass scale culturing of hairy roots. Development of bioreactor models for hairy root cultures is still a recent phenomenon. It is also necessary to develop computer-aided models for different parameters such as oxygen consumption and excretion of product to the medium. Further, transformed roots are able to regenerate genetically stable plants as transgenics or clones. This property of rapid growth and high plantlet regeneration frequency allows clonal propagation of elite plants. In addition, the altered phenotype of hairy root regenerants (hairy root syndrome) is useful in plant breeding programs with plants of ornamental interest. In vitro transformation and regeneration from hairy roots facilitates application of biotechnology to tree species. The ability to manipulate trees at a cellular and molecular level shows great potential for clonal propagation and genetic improvement. Transgenic root system offers tremendous potential for introducing additional genes along with the Ri T-DNA genes for alteration of metabolic pathways and production of useful metabolites or compounds of interest. This article discusses various applications and perspectives of hairy root cultures and the recent progress achieved with respect to transformation of plants using A. rhizogenes.

Large-scale plant cell culture: methods, applications and products

Recent significant contributions to the design of large-scale plant cell cultures for secondary metabolite production include: the development of a strategy to control the concentration of dissolved gases at constant shear; a surface immobilization technique to retain cell mass at high mixing rates; and a modified stirred-tank reactor with a mesh cage to prevent damage of hairy root cultures.