Plant regeneration from hairy-root cultures transformed by infection with Agrobacterium rhizogenes in Catharanthus roseus

Enhanced root system architecture in oilseed rape transformed with Rhizobium rhizogenes

Transformation of plants using wild strains of agrobacteria is termed natural transformation and is not covered by GMO legislation in e.g. European Union and Japan. In the current study, offspring lines (A11 and B3) of Rhizobium rhizogenes naturally transformed oilseed rape (Brassica napus) were randomly selected to characterize the morphological traits, and analyze the implications of such morphological changes on plant drought resilience. It was found that the introduction of Ri-genes altered the biomass partitioning to above- and under-ground parts of oilseed rape plants. Compared to the wild type (WT), the A11 and B3 lines exhibited 1.2-4.0 folds lower leaf and stem dry weight, leaf area and plant height, but had 1.3-5.8 folds greater root dry weight, root length and root surface area, resulting in a significantly enhanced root: shoot dry mass ratio and root surface area: leaf area ratio. In addition, the introduction of Ri-genes conferred reduced stomatal pore aperture and increased stomatal density in the B3 line, and increased leaf thickness in A11 line, which could benefit plant drought resilience. Finally, the modulations in morphological traits as a consequence of transformation with Ri-genes are discussed concerning resilience in water-limited conditions. These findings reveal the potential of natural transformation with R. rhizogenes for drought-targeted breeding in crops.

Characterization of the ZCTs, a subgroup of Cys2-His2 zinc finger transcription factors regulating alkaloid biosynthesis in Catharanthus roseus

KEY MESSAGE

The C. roseus ZCTs are jasmonate-responsive, can be induced by CrMYC2a, and can act as significant regulators of the terpenoid indole alkaloid pathway when highly expressed. Catharanthus roseus is the sole known producer of the anti-cancer terpenoid indole alkaloids (TIAs), vinblastine and vincristine. While the enzymatic steps of the pathway have been elucidated, an understanding of its regulation is still emerging. The present study characterizes an important subgroup of Cys2-His2 zinc finger transcription factors known as Zinc finger Catharanthus Transcription factors (ZCTs). We identified three new ZCT members (named ZCT4, ZCT5, and ZCT6) that clustered with the putative repressors of the TIA pathway, ZCT1, ZCT2, and ZCT3. We characterized the role of these six ZCTs as potential redundant regulators of the TIA pathway, and their tissue-specific and jasmonate-responsive expression. These ZCTs share high sequence conservation in their two Cys2-His2 zinc finger domains but differ in the spacer length and sequence between these zinc fingers. The transient overexpression of ZCTs in seedlings significantly repressed the promoters of the terpenoid (pLAMT) and condensation branch (pSTR1) of the TIA pathway, consistent with that previously reported for ZCT1, ZCT2, and ZCT3. In addition, ZCTs significantly repressed and indirectly activated several promoters of the vindoline pathway (not previously studied). The ZCTs differed in their tissue-specific expression but similarly increased with jasmonate in a dosage-dependent manner (except for ZCT5). We showed significant activation of the pZCT1 and pZCT3 promoters by the de-repressed CrMYC2a, suggesting that the jasmonate-responsive expression of the ZCTs can be mediated by CrMYC2a. In summary, the C. roseus ZCTs are jasmonate-responsive, can be induced by CrMYC2a, and can act as significant regulators of the TIA pathway when highly expressed.

An update on biotechnological intervention mediated by plant tissue culture to boost secondary metabolite production in medicinal and aromatic plants

Since prehistoric times, medicinal and aromatic plants (MAPs) have been employed for various therapeutic purposes due to their varied array of pharmaceutically relevant bioactive compounds, i.e. secondary metabolites. However, when secondary metabolites are isolated directly from MAPs, there is occasionally very poor yield and limited synthesis of secondary metabolites from particular tissues and certain developmental stages. Moreover, many MAPs species are in danger of extinction, especially those used in pharmaceuticals, as their natural populations are under pressure from overharvesting due to the excess demand for plant-based herbal remedies. The extensive use of these metabolites in a number of industrial and pharmaceutical industries has prompted a call for more research into increasing the output via optimization of large-scale production using plant tissue culture techniques. The potential of plant cells as sources of secondary metabolites can be exploited through a combination of product recovery technology research, targeted metabolite production, and in vitro culture establishment. The plant tissue culture approach provides low-cost, sustainable, continuous, and viable secondary metabolite production that is not affected by geographic or climatic factors. This study covers recent advancements in the induction of medicinally relevant metabolites, as well as the conservation and propagation of plants by advanced tissue culture technologies.

Critical parameters for robust Agrobacterium-mediated transient transformation and quantitative promoter assays in Catharanthus roseus seedlings

Agrobacterium-mediated transient expression methods are widely used to study gene function in both model and non-model plants. Using a dual-luciferase assay, we quantified the effect of Agrobacterium-infiltration parameters on the transient transformation efficiency of Catharanthus roseus seedlings. We showed that transformation efficiency is highly sensitive to seedling developmental state and a pre- and post-infiltration dark incubation and is less sensitive to the Agrobacterium growth stage. For example, 5 versus 6 days of germination in the dark increased seedling transformation efficiency by seven- to eight-fold while a dark incubation pre- and post-infiltration increased transformation efficiency by five- to 13-fold. Agrobacterium in exponential compared with stationary phase increased transformation efficiency by two-fold. Finally, we quantified the variation in our Agrobacterium-infiltration method in replicate infiltrations and experiments. Within a given experiment, significant differences of up to 2.6-fold in raw firefly luciferase (FLUC) and raw Renilla luciferase (RLUC) luminescence occurred in replicate infiltrations. These differences were significantly reduced when FLUC was normalized to RLUC values, highlighting the utility of including a reference reporter to minimize false positives. Including a second experimental replicate further reduced the potential for false positives. This optimization and quantitative validation of Agrobacterium infiltration in C. roseus seedlings will facilitate the study of this important medicinal plant and will expand the application of Agrobacterium-mediated transformation methods in other plant species.

Agrobacterium rhizogenes-mediated marker-free transformation and gene editing system revealed that AeCBL3 mediates the formation of calcium oxalate crystal in kiwifruit

The transformation and gene editing of the woody species kiwifruit are difficult and time-consuming. The fast and marker-free genetic modification system for kiwifruit has not been developed yet. Here, we establish a rapid and efficient marker-free transformation and gene editing system mediated by Agrobacterium rhizogenes for kiwifruit. Moreover, a removing-root-tip method was developed to significantly increase the regeneration efficiency of transgenic hairy roots. Through A. rhizogenes-mediated CRISPR/Cas9 gene editing, the editing efficiencies of CEN4 and AeCBL3 achieved 55 and 50%, respectively. And several homozygous knockout lines for both genes were obtained. Our method has been successfully applied in the transformation of two different species of kiwifruit (Actinidia chinensis 'Hongyang' and A.eriantha 'White'). Next, we used the method to study the formation of calcium oxalate (CaOx) crystals in kiwifruit. To date, little is known about how CaOx crystal is formed in plants. Our results indicated that AeCBL3 overexpression enhanced CaOx crystal formation, but its knockout via CRISPR/Cas9 significantly impaired crystal formation in kiwifruit. Together, we developed a fast maker-free transformation and highly efficient CRISPR-Cas9 gene editing system for kiwifruit. Moreover, our work revealed a novel gene mediating CaOx crystal formation and provided a clue to elaborate the underlying mechanisms.

The History of Agrobacterium Rhizogenes: From Pathogen to a Multitasking Platform for Biotechnology

Agrobacterium's journey has been a roller coaster, from being a pathogen to becoming a powerful biotechnological tool. While A. tumefaciens has provided the scientific community with a versatile tool for plant transformation, Agrobacterium rhizogenes has given researchers a Swiss army knife for developing many applications. These applications range from a methodology to regenerate plants, often recalcitrant, to establish bioremediation protocols to a valuable system to produce secondary metabolites. This chapter reviews its discovery, biology, controversies over its nomenclature, and some of the multiple applications developed using A. rhizogenes as a platform.

Small RNA-Seq to Unveil the miRNA Expression Patterns and Identify the Target Genes in Panax ginseng

Panax ginseng, renowned for its medicinal properties, relies on adventitious roots and hairy roots as crucial sources for the production of ginsenosides. Despite the widespread utilization of ginseng, investigations into its miRNAs have remained scarce. To address this gap, two samples of ginseng adventitious roots and ginseng hairy roots were collected, and subsequent construction and sequencing of small RNA libraries of ginseng adventitious roots and hairy roots were performed using the Illumina HiSeq X Ten platform. The analysis of the sequencing data unveiled total miRNAs 2432. The miR166 and miR396 were the most highly expressed miRNA families in ginseng. The miRNA expression analysis results were used to validate the qRT-PCR. Target genes of miRNA were predicted and GO function annotation and KEGG pathway analysis were performed on target genes. It was found that miRNAs are mainly involved in synthetic pathways and biological processes in plants, which include metabolic and bioregulatory processes. The plant miRNAs enriched KEGG pathways are associated with some metabolism, especially amino acid metabolism and carbohydrate metabolism. These results provide valuable insights miRNAs and their roles in metabolic processes in ginseng.

Improved and Highly Efficient Agrobacterium rhizogenes-Mediated Genetic Transformation Protocol: Efficient Tools for Functional Analysis of Root-Specific Resistance Genes for Solanum lycopersicum cv. Micro-Tom

Gene function analysis, molecular breeding, and the introduction of new traits in crop plants all require the development of a high-performance genetic transformation system. In numerous crops, including tomatoes, Agrobacterium-mediated genetic transformation is the preferred method. As one of our ongoing research efforts, we are in the process of mapping a broad-spectrum nematode resistance gene (Me1) in pepper. We work to transform tomato plants with candidate genes to confer resistance to nematodes in Solanaceae members. The transformation technology development is designed to produce a reproducible, rapid, and highly effective Agrobacterium-mediated genetic transformation system of Micro-Tom. In our system, a transformation efficiency of over 90% was achieved. The entire procedure, starting from the germination of seeds to the establishment of transformed plants in soil, was completed in 53 days. We confirmed the presence of the NeoR/KanR and DsRed genes in the transformed roots by polymerase chain reaction. The hairy root plants were infected with nematodes, and after 3 months, the presence of DsRed and NeoR/KanR genes was detected in the transformant roots to confirm the long-term effectiveness of the method. The presented study may facilitate root-related research and exploration of root–pathogen interactions.

Optimization of Tissue Culturing and Genetic Transformation Protocol for Casuarina equisetifolia

Casuarina equisetifolia is widely used in agroforestry plantations for soil stabilization, ecosystem rehabilitation, reclamation, and coastal protection. Moreover, C. equisetifolia has remarkable resistance to typhoons, desert, low soil fertility, drought, and salinity, but not cold. Therefore, it is significant to breed high-quality Casuarina varieties to improve the tolerance and adaptability to cold weather by molecular techniques. The establishment of a rapid and efficient callus induction and regeneration system via tissue culture is pre-requisite for the genetic transformation of C. equisetifolia, which is so far lacking. In this study, we reported an efficient and rapid regeneration system using stem segment explants, in which callus induction was found to be optimal in a basal medium supplemented with 0.1 mg⋅L^-1 TDZ and 0.1 mg⋅L^-1 NAA, and proliferation in a basal medium containing 0.1 mg⋅L^-1 TDZ and 0.5 mg⋅L^-1 6-BA. For bud regeneration and rooting, the preferred plant growth regulator (PGR) in basal medium was 0.5 mg⋅L^-1 6-BA, and a combination of 0.02 mg⋅L^-1 IBA and 0.4 mg⋅L^-1 IAA, respectively. We also optimized genetic a transformation protocol using Agrobacterium tumefaciens harboring the binary vector pCAMBIA1301 with β-glucuronidase (GUS) as a reporter gene. Consequently, 5 mg L^-1 hygromycin, 20 mg L^-1 acetosyringone (As), and 2 days of co-cultivation duration were optimized to improve the transformation efficiency. With these optimized parameters, transgenic plants were obtained in about 4 months. Besides that, Agrobacterium rhizogenes-mediated transformation involving adventitious root induction was also optimized. Our findings will not only increase the transformation efficiency but also shorten the time for developing transgenic C. equisetifolia plants. Taken together, this pioneer study on tissue culturing and genetic transformation of C. equisetifolia will pave the way for further genetic manipulation and functional genomics of C. equisetifolia.

Compact shoot architecture of Osteospermum fruticosum transformed with Rhizobium rhizogenes

Improved compact shoot architecture of Osteospermum fruticosum Ri lines obtained through Rhizobium rhizogenes transformation reduces the need for chemical growth retardants. Compactness is for many ornamental crops an important commercial trait that is usually obtained through the application of growth retardants. Here, we have adopted a genetic strategy to introduce compactness in the perennial shrub Cape daisy (Osteospermum fruticosum Norl.). To this end, O. fruticosum was transformed using six different wild type Rhizobium rhizogenes strains. The most effective R. rhizogenes strains Arqua1 and ATCC15834 were used to create hairy root cultures from six Cape daisy genotypes. These root cultures were regenerated to produce transgenic Ri lines, which were analyzed for compactness. Ri lines displayed the characteristic Ri phenotype, i.e., reduced plant height, increased branching, shortened internodes, shortened peduncles, and smaller flowers. Evaluation of the Ri lines under commercial production conditions showed that similar compactness was obtained as the original Cape daisy genotypes treated with growth retardant. The results suggest that the use of chemical growth retardants may be omitted or reduced in commercial production systems of Cape daisy through implementation of Ri lines in future breeding programs.

Biotechnological advancements in Catharanthus roseus (L.) G. Don

Catharanthus roseus (L.) G. Don, also known as Madagascar periwinkle or Sadabahar, is a herbaceous plant belonging to the family Apocynaceae. Being a reservoir for more than 200 alkaloids, it reserves a place for itself in the list of important medicinal plants. Secondary metabolites are present in its leaves (e.g., vindoline, vinblastine, catharanthine, and vincristine) as well as basal stem and roots (e.g., ajmalicine, reserpine, serpentine, horhammericine, tabersonine, leurosine, catharanthine, lochnerine, and vindoline). Two of its alkaloids, vincristine and vinblastine (possessing anticancerous properties), are being used copiously in pharmaceutical industries. Till date, arrays of reports are available on in vitro biotechnological improvements of C. roseus. The present review article concentrates chiefly on various biotechnological advancements based on plant tissue culture techniques of the last three decades, for instance, regeneration via direct and indirect organogenesis, somatic embryogenesis, secondary metabolite production, synthetic seed production, clonal fidelity assessment, polyploidization, genetic transformation, and nanotechnology. It also portrays the importance of various factors influencing the success of in vitro biotechnological interventions in Catharanthus and further addresses several shortcomings that can be further explored to create a platform for upcoming innovative approaches. KEY POINTS: • C. roseus yields anticancerous vincristine and vinblastine used in pharma industry. •In vitro biotechnological interventions prompted major genetic advancements. • This review provides an insight on in vitro-based research achievements till date. • Key bottlenecks and prospective research methodologies have been identified herein.

Rhizogenic agrobacteria as an innovative tool for plant breeding: current achievements and limitations

Compact plant growth is an economically important trait for many crops. In practice, compactness is frequently obtained by applying chemical plant growth regulators. In view of sustainable and environmental-friendly plant production, the search for viable alternatives is a priority for breeders. Co-cultivation and natural transformation using rhizogenic agrobacteria result in morphological alterations which together compose the Ri phenotype. This phenotype is known to exhibit a more compact plant habit, besides other features. In this review, we highlight the use of rhizogenic agrobacteria and the Ri phenotype with regard to sustainable plant production and plant breeding. An overview of described Ri lines and current breeding applications is presented. The potential of Ri lines as pre-breeding material is discussed from both a practical and legal point of view.

EASI Transformation: An Efficient Transient Expression Method for Analyzing Gene Function in Catharanthus roseus Seedlings

The Catharanthus roseus plant is the exclusive source of the valuable anticancer terpenoid indole alkaloids, vinblastine (VB) and vincristine (VC). The recent availability of transcriptome and genome resources for C. roseus necessitates a fast and reliable method for studying gene function. In this study, we developed an Agrobacterium-mediated transient expression method to enable the functional study of genes rapidly in planta, conserving the compartmentalization observed in the VB and VC pathway. We focused on (1) improving the transformation method (syringe versus vacuum agroinfiltration) and cultivation conditions (seedling age, Agrobacterium density, and time point of maximum transgene expression), (2) improving transformation efficiency through the constitutive expression of the virulence genes and suppressing RNA silencing mechanisms, and (3) improving the vector design by incorporating introns, quantitative and qualitative reporter genes (luciferase and GUS genes), and accounting for transformation heterogeneity across the tissue using an internal control. Of all the parameters tested, vacuum infiltration of young seedlings (10-day-old, harvested 3 days post-infection) resulted in the strongest increase in transgene expression, at 18 - 57 fold higher than either vacuum or syringe infiltration of other seedling ages. Endowing the A. tumefaciens strain with the mutated VirGN54D or silencing suppressors within the same plasmid as the reporter gene further increased expression by 2 - 10 fold. For accurate measurement of promoter transactivation or activity, we included an internal control to normalize the differences in plant mass and transformation efficiency. Including the normalization gene (Renilla luciferase) on the same plasmid as the reporter gene (firefly luciferase) consistently yielded a high signal and a high correlation between RLUC and FLUC. As proof of principle, we applied this approach to investigate the regulation of the CroSTR1 promoter with the well-known activator ORCA3 and repressor ZCT1. Our method demonstrated the quantitative assessment of both the activation and repression of promoter activity in C. roseus. Our efficient Agrobacterium-mediated seedling infiltration (EASI) protocol allows highly efficient, reproducible, and homogenous transformation of C. roseus cotyledons and provides a timely tool for the community to rapidly assess the function of genes in planta, particularly for investigating how transcription factors regulate terpenoid indole alkaloid biosynthesis.

Cross-family transcription factor interaction between MYC2 and GBFs modulates terpenoid indole alkaloid biosynthesis

Biosynthesis of medicinally valuable terpenoid indole alkaloids (TIAs) in Catharanthus roseus is regulated by transcriptional activators such as the basic helix-loop-helix factor CrMYC2. However, the transactivation effects are often buffered by repressors, such as the bZIP factors CrGBF1 and CrGBF2, possibly to fine-tune the accumulation of cytotoxic TIAs. Questions remain as to whether and how these factors interact to modulate TIA production. We demonstrated that overexpression of CrMYC2 induces CrGBF expression and results in reduced alkaloid accumulation in C. roseus hairy roots. We found that CrGBF1 and CrGBF2 form homo- and heterodimers to repress the transcriptional activities of key TIA pathway gene promoters. We showed that CrGBFs dimerize with CrMYC2, and CrGBF1 binds to the same cis-elements (T/G-box) as CrMYC2 in the target gene promoters. Our findings suggest that CrGBFs antagonize CrMYC2 transactivation possibly by competitive binding to the T/G-box in the target promoters and/or protein-protein interaction that forms a non-DNA binding complex that prevents CrMYC2 from binding to its target promoters. Homo- and heterodimer formation allows fine-tuning of the amplitude of TIA gene expression. Our findings reveal a previously undescribed regulatory mechanism that governs the TIA pathway genes to balance metabolic flux for TIA production in C. roseus.

Agrobacterium rhizogenes-mediated transformation of a dioecious plant model Silene latifolia

Silene latifolia serves as a model species to study dioecy, the evolution of sex chromosomes, dosage compensation and sex-determination systems in plants. Currently, no protocol for genetic transformation is available for this species, mainly because S. latifolia is considered recalcitrant to in vitro regeneration and infection with Agrobacterium tumefaciens. Using cytokinins and their synthetic derivatives, we markedly improved the efficiency of regeneration. Several agrobacterial strains were tested for their ability to deliver DNA into S. latifolia tissues leading to transient and stable expression of the GUS reporter. The use of Agrobacterium rhizogenes strains resulted in the highest transformation efficiency (up to 4.7% of stable transformants) in hairy root cultures. Phenotypic and genotypic analyses of the T1 generation suggested that the majority of transformation events contain a small number of independent T-DNA insertions and the transgenes are transmitted to the progeny in a Mendelian pattern of inheritance. In short, we report an efficient and reproducible protocol for leaf disc transformation and subsequent plant regeneration in S. latifolia, based on the unique combination of infection with A. rhizogenes and plant regeneration from hairy root cultures using synthetic cytokinins. A protocol for the transient transformation of S.latifolia protoplasts was also developed and applied to demonstrate the possibility of targeted mutagenesis of the sex linked gene SlAP3 by TALENs and CRISPR/Cas9.

A network of jasmonate-responsive bHLH factors modulate monoterpenoid indole alkaloid biosynthesis in Catharanthus roseus

The pharmaceutically valuable monoterpene indole alkaloids (MIAs) in Catharanthus roseus are derived from the indole and iridoid pathways that respond to jasmonate (JA) signaling. Two classes of JA-responsive bHLH transcription factor (TF), CrMYC2 and BIS1/BIS2, are known to regulate the indole and iridoid pathways, respectively. However, upregulation of either one of the TF genes does not lead to increased MIA accumulation. Moreover, little is known about the interconnection between the CrMYC2 and BIS transcriptional cascades and the hierarchical position of BIS1/BIS2 in JA signaling. Here, we report that a newly identified bHLH factor, Repressor of MYC2 Targets 1 (RMT1), is activated by CrMYC2 and BIS1, and acts as a repressor of the CrMYC2 targets. In addition, we isolated and functionally characterized the core C. roseus JA signaling components, including CORONATINE INSENSITIVE 1 (COI1) and JASMONATE ZIM domain (JAZ) proteins. CrMYC2 and BIS1 are repressed by the JAZ proteins in the absence of JA, but de-repressed by the SCF^COI1 complex on perception of JA. Our findings suggest that the repressors, JAZs and RMT1, mediate crosstalk between the CrMYC2 and BIS regulatory cascades to balance the metabolic flux in MIA biosynthesis.

Terpene Moiety Enhancement by Overexpression of Geranyl(geranyl) Diphosphate Synthase and Geraniol Synthase Elevates Monomeric and Dimeric Monoterpene Indole Alkaloids in Transgenic Catharanthus roseus

Catharanthus roseus is the sole source of two of the most important anticancer monoterpene indole alkaloids (MIAs), vinblastine and vincristine and their precursors, vindoline and catharanthine. The MIAs are produced from the condensation of precursors derived from indole and terpene secoiridoid pathways. It has been previously reported that the terpene moiety limits MIA biosynthesis in C. roseus. Here, to overcome this limitation and enhance MIAs levels in C. roseus, bifunctional geranyl(geranyl) diphosphate synthase [G(G)PPS] and geraniol synthase (GES) that provide precursors for early steps of terpene moiety (secologanin) formation, were overexpressed transiently by agroinfiltration and stably by Agrobacterium-mediated transformation. Both transient and stable overexpression of G(G)PPS and co-expression of G(G)PPS+GES significantly enhanced the accumulation of secologanin, which in turn elevated the levels of monomeric MIAs. In addition, transgenic C. roseus plants exhibited increased levels of root alkaloid ajmalicine. The dimeric alkaloid vinblastine was enhanced only in G(G)PPS but not in G(G)PPS+GES transgenic lines that correlated with transcript levels of peroxidase-1 (PRX1) involved in coupling of vindoline and catharanthine into 3',4'-anhydrovinblastine, the immediate precursor of vinblastine. Moreover, first generation (T₁) lines exhibited comparable transcript and metabolite levels to that of T₀ lines. In addition, transgenic lines displayed normal growth similar to wild-type plants indicating that the bifunctional G(G)PPS enhanced flux toward both primary and secondary metabolism. These results revealed that improved availability of early precursors for terpene moiety biosynthesis enhanced production of MIAs in C. roseus at the whole plant level. This is the first report demonstrating enhanced accumulation of monomeric and dimeric MIAs including root MIA ajmalicine in C. roseus through transgenic approaches.

Differential rubisco content and photosynthetic efficiency of rol gene integrated Vinca minor transgenic plant: Correlating factors associated with morpho-anatomical changes, gene expression and alkaloid productivity

Transgenic plants obtained from a hairy root line (PVG) of Vinca minor were characterized in relation to terpenoid indole alkaloids (TIAs) pathway gene expression and vincamine production. The hairy roots formed callus with green nodular protuberances when transferred onto agar-gelled MS medium containing 3.0mg/l zeatin. These meristematic zones developed into shoot buds on medium with 1.0mg/l 2, 4-dichlorophenoxyacetic acid and 40mg/l ascorbic acid. These shoot buds subsequently formed rooted plants when shifted onto a hormone-free MS medium with 6% sucrose. Transgenic nature of the plants was confirmed by the presence of rol genes of the Ri plasmid in them. The transgenic plants (TP) had elongated internodes and a highly proliferating root system. During glass house cultivation TP consistently exhibited slower growth rate, low chlorophyll content (1.02±0.08mg/gm fr. wt.), reduced carbon exchange rate (2.67±0.16μmolm^-2s^-1), less transpiration rate (2.30±0.20mmolm^-2 s^-1) and poor stomatal conductance (2.21±0.04mmolm^-2 s^-1) when compared with non-transgenic population. The activity of rubisco enzyme in the leaves of TP was nearly two folds less in comparison to non-transgenic controls (1.80milliunitsml^-1mgprotein^-1 against 3.61milliunits ml^-1mgprotein^-1, respectively). Anatomically, the TP had a distinct tetarch arrangement of vascular bundles in their stem and roots against a typical ployarched pattern in the non-transgenic plants. Significantly, the transgenic plants accumulated 35% higher amount of total TIAs (3.10±0.21% dry wt.) along with a 0.03% dry wt. content of its vasodilatory and nootropic alkaloid vincamine in their leaves. Higher productivity of alkaloids in TP was corroborated with more than four (RQ=4.60±0.30) and five (RQ=5.20±0.70) times over-expression of TIAs pathway genes tryptophan decarboxylase (TDC) and strictosidine synthase (STR) that are responsible for pushing the metabolic flux towards TIAs synthesis in this medicinal herb.

Biologically active recombinant human erythropoietin expressed in hairy root cultures and regenerated plantlets of Nicotiana tabacum L

Hairy root culture is a potential alternative to conventional mammalian cell culture to produce recombinant proteins due to its ease in protein recovery, low costs and absence of potentially human pathogenic contaminants. The current study focussed to develop a new platform of a hairy root culture system from Nicotiana tabacum for the production of recombinant human EPO (rhEPO), which is regularly produced in mammalian cells. The human EPO construct was amplified with C-terminal hexahistidine tag from a cDNA of Caco-2 cells. Two versions of rhEPO clones, with or without the N-terminal calreticulin (cal) fusion sequence, were produced by cloning the amplified construct into gateway binary vector pK7WG2D. Following Agrobacterium rhizogenes mediated transformation of tobacco explants; integration and expression of constructs in hairy roots were confirmed by several tests at DNA, RNA and protein levels. The amount of intracellular rhEPO from hairy root cultures with cal signal peptide was measured up to 66.75 ng g-1 of total soluble protein. The presence of the ER signal peptide (cal) was essential for the secretion of rhEPO into the spent medium; no protein was detected from hairy root cultures without ER signal peptide. The addition of polyvinylpyrrolidone enhanced the stabilization of secreted rhEPO leading to a 5.6 fold increase to a maximum concentration of 185.48 pg rhEPOHR g-1 FW hairy root cultures. The rhizo-secreted rhEPO was separated by HPLC and its biological activity was confirmed by testing distinct parameters for proliferation and survival in retinal pigment epithelial cells (ARPE). In addition, the rhEPO was detected to an amount 14.8 ng g-1 of total soluble leaf protein in transgenic T0 generation plantlets regenerated from hairy root cultures with cal signal peptide.

The Agrobacterium rhizogenes oncogenes rolB and ORF13 increase formation of generative shoots and induce dwarfism in Arabidopsis thaliana (L.) Heynh

Plant transformation with the wild type Ri plasmid T-DNA of Agrobacterium rhizogenes is a promising method for breeding of compact plants and has been the subject of numerous studies. However, knowledge concerning the isolated functions of single genes and ORFs from the plasmid is limited. The rolB and ORF13 oncogenes of A. rhizogenes show considerable promise in plant breeding, but have not been comprehensively studied. Detailed information regarding the morphological impact of specific genes of the Ri plasmid will allow for optimized targeted breeding of plants transformed with the wild type Ri plasmid T-DNA. rolB and ORF13 were recombined into the genome of Arabidopsis thaliana using Gateway^® cloning and the effect on plant growth was assessed biometrically throughout the plants' life cycle. rolB-lines exhibited dwarfing, early necrosis of rosette leaves, altered leaf and flower morphology, and developed an increased number of inflorescences per rosette area compared to the wild type. ORF13-lines were extremely dwarfed, attaining only ca. 1% of the rosette area of the wild type, leaf and flower size was reduced, and the shape modified. The study documents that the traits inferred by the rolB oncogene yield plants with increased formation of generative shoots, but also result in some degree of premature senescence of vegetative organs. The extreme dwarfism seen in ORF13-lines indicate that this oncogene may be more important in the dwarfing response of plants transformed with the wild type Ri plasmid T-DNA than previously assumed and that transformation with this oncogene induces a very compact phenotype.

Screening and kinetic studies of catharanthine and ajmalicine accumulation and their correlation with growth biomass in Catharanthus roseus hairy roots

Context Catharanthus roseus (L.) G. Don (Apocynaceae) is still one of the most important sources of terpene indole alkaloids including anticancer and hypertensive drugs as vincristine and vinblastine. These final compounds have complex pathway and many enzymes are involved in their biosynthesis. Indeed, ajmalicine and catharanthine are important precursors their increase can lead to enhance levels of molecules of interest. Objective This study aims at selecting the highest yield of hairy root line(s) and at identifying best times for further treatments. We study kinetics growth and alkaloids (ajmalicine and catharanthine) accumulation of three selected hairy root lines during the culture cycle in order to determine the relationship between biomass production and alkaloids accumulation. Materials and methods Comparative analysis has been carried out on three selected lines of Catharanthus roseus hairy roots (LP10, LP21 and L54) for their kinetics of growth and the accumulation of ajamalicine and catharanthine, throughout a 35-day culture cycle. The methanolic extract for each line in different times during culture cycle is analyzed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Results Maximum accumulation of the alkaloids is recorded for LP10 line in which the peak of ajmalicine and catharanthine accumulation reached to 3.8 and 4.3 mg/g dry weight (DW), respectively. This increase coincides with an exponential growth phase. Discussion and conclusion Our results suggest that the evolution of accumulation of ajmalicine and catharanthine are positively correlated with the development of the biomass growth. Significantly, for LP10 line the most promising line to continue optimizing the production of TIAs. Additionally, the end of exponential phase remains the best period for elicitor stimuli.

Overexpression of the gibberellin 2-oxidase gene from Torenia fournieri induces dwarf phenotypes in the liliaceous monocotyledon Tricyrtis sp

Gibberellins (GAs) are the plant hormones that control many aspects of plant growth and development, including stem elongation. Genes encoding enzymes related to the GA biosynthetic and metabolic pathway have been isolated and characterized in many plant species. Gibberellin 2-oxidase (GA2ox) catalyzes bioactive GAs or their immediate precursors to inactive forms; therefore, playing a direct role in determining the levels of bioactive GAs. In the present study, we produced transgenic plants of the liliaceous monocotyledon Tricyrtis sp. overexpressing the GA2ox gene from the linderniaceous dicotyledon Torenia fournieri (TfGA2ox2). All six transgenic plants exhibited dwarf phenotypes, and they could be classified into two classes according to the degree of dwarfism: three plants were moderately dwarf and three were severely dwarf. All of the transgenic plants had small or no flowers, and smaller, rounder and darker green leaves. Quantitative real-time reverse transcription-polymerase chain reaction (PCR) analysis showed that the TfGA2ox2 expression level generally correlated with the degree of dwarfism. The endogenous levels of bioactive GAs, GA1 and GA4, largely decreased in transgenic plants as shown by liquid chromatography-mass spectrometry (LC-MS) analysis, and the level also correlated with the degree of dwarfism. Exogenous treatment of transgenic plants with gibberellic acid (GA3) resulted in an increased shoot length, indicating that the GA signaling pathway might normally function in transgenic plants. Thus, morphological changes in transgenic plants may result from a decrease in the endogenous levels of bioactive GAs. Finally, a possibility of molecular breeding for plant form alteration in liliaceous ornamental plants by genetically engineering the GA metabolic pathway is discussed.

Induction of hairy roots in Arnica montana L. by Agrobacterium rhizogenes

The induction of hairy roots in Arnica montana L. by Agrobacterium rhizogenes mediated system was established. The frequency of genetic transformation varied from 4.8 to 12% depended on method of infection. The cefotaxime at concentration of 200 mg/l proved to suppress effectively the growth of A. rhizogenes after co-cultivation. Among the three tested nutrient media: Murashige and Skoog (MS), Gamborg’s (B5) and Schenk and Hildebrandt (SH), MS medium was superior for growth and high biomass production of transformed roots compared to other culture media. After culturing for 40 days the fresh weight of clone T4 increased 7.6 fold over the non-transformed roots. The transfer of rol A, rol B and rol C genes into Arnica genome was confirmed by PCR analysis. Established genetic transformation techniques in A. montana efficiently provided and generated a large number of transformed roots — an excellent system for studying gene function and could be used for the production of secondary metabolites synthesized in roots.

Genetic engineering and sustainable production of ornamentals: current status and future directions

Through the last decades, environmentally and health-friendly production methods and conscientious use of resources have become crucial for reaching the goal of a more sustainable plant production. Protection of the environment requires careful consumption of limited resources and reduction of chemicals applied during production of ornamental plants. Numerous chemicals used in modern plant production have negative impacts on human health and are hazardous to the environment. In Europe, several compounds have lost their approval and further legal restrictions can be expected. This review presents the more recent progress of genetic engineering in ornamental breeding, delivers an overview of the biological background of the used technologies and critically evaluates the usefulness of the strategies to obtain improved ornamental plants. First, genetic engineering is addressed as alternative to growth retardants, comprising recombinant DNA approaches targeting relevant hormone pathways, e.g. the gibberellic acid (GA) pathway. A reduced content of active GAs causes compact growth and can be facilitated by either decreased anabolism, increased catabolism or altered perception. Moreover, compactness can be accomplished by using a natural transformation approach without recombinant DNA technology. Secondly, metabolic engineering approaches targeting elements of the ethylene signal transduction pathway are summarized as a possible alternative to avoid the use of chemical ethylene inhibitors. In conclusion, molecular breeding approaches are dealt with in a way allowing a critical biological assessment and enabling the scientific community and public to put genetic engineering of ornamental plants into a perspective regarding their usefulness in plant breeding.

Development of efficient Catharanthus roseus regeneration and transformation system using agrobacterium tumefaciens and hypocotyls as explants

BACKGROUND

As a valuable medicinal plant, Madagascar periwinkle (Catharanthus roseus) produces many terpenoid indole alkaloids (TIAs), such as vindoline, ajamlicine, serpentine, catharanthine, vinblastine and vincristine et al. Some of them are important components of drugs treating cancer and hypertension. However, the yields of these TIAs are low in wild-type plants, and the total chemical synthesis is impractical in large scale due to high-cost and their complicated structures. The recent development of metabolic engineering strategy offers a promising solution. In order to improve the production of TIAs in C. roseus, the establishment of an efficient genetic transformation method is required.

RESULTS

To develop a genetic transformation method for C. roseus, Agrobacterium tumefaciens strain EHA105 was employed which harbors a binary vector pCAMBIA2301 containing a report β-glucuronidase (GUS) gene and a selectable marker neomycin phosphotransferase II gene (NTPII). The influential factors were investigated systematically and the optimal transformation condition was achieved using hypocotyls as explants, including the sonication treatment of 10 min with 80 W, A. tumefaciens infection of 30 min and co-cultivation of 2 d in 1/2 MS medium containing 100 μM acetosyringone. With a series of selection in callus, shoot and root inducing kanamycin-containing resistance media, we successfully obtained stable transgenic regeneration plants. The expression of GUS gene was confirmed by histochemistry, polymerase chain reaction, and genomic southern blot analysis. To prove the efficiency of the established genetic transformation system, the rate-limiting gene in TIAs biosynthetic pathway, DAT, which encodes deacetylvindoline-4-O-acetyltransferase, was transferred into C. roseus using this established system and 9 independent transgenic plants were obtained. The results of metabolite analysis using high performance liquid chromatography (HPLC) showed that overexpression of DAT increased the yield of vindoline in transgenic plants.

CONCLUSIONS

In the present study, we report an efficient Agrobacterium-mediated transformation system for C. roseus plants with 11% of transformation frequency. To our knowledge, this is the first report on the establishment of A. tumefaciens mediated transformation and regeneration of C. roseus. More importantly, the C. roseus transformation system developed in this work was confirmed in the successful transformation of C. roseus using a key gene DAT involved in TIAs biosynthetic pathway resulting in the higher accumulation of vindoline in transgenic plants.

Striga parasitizes transgenic hairy roots of Zea mays and provides a tool for studying plant-plant interactions

BACKGROUND

Striga species are noxious root hemi-parasitic weeds that debilitate cereal production in sub-Saharan Africa (SSA). Control options for Striga are limited and developing Striga resistant crop germplasm is regarded as the best and most sustainable control measure. Efforts to improve germplasm for Striga resistance by a non-Genetic Modification (GM) approach, for example by exploiting natural resistance, or by a GM approach are constrained by limited information on the biological processes underpinning host-parasite associations. Additionaly, a GM approach is stymied by lack of availability of candidate resistance genes for introduction into hosts and robust transformation methods to validate gene functions. Indeed, a majority of Striga hosts, the world's most cultivated cereals, are recalcitrant to genetic transformation. In maize, the existing protocols for transformation and regeneration are tedious, lengthy, and highly genotype-specific with low efficiency of transformation.

RESULTS

We used Agrobacterium rhizogenes strain K599 carrying a reporter gene construct, Green Fluorescent Protein (GFP), to generate transgenic composite maize plants that were challenged with the parasitic plant Striga hermonthica. Eighty five percent of maize plants produced transgenic hairy roots expressing GFP. Consistent with most hairy roots produced in other species, transformed maize roots exhibited a hairy root phenotype, the hallmark of A. rhizogenes mediated transformation. Transgenic hairy roots resulting from A. rhizogenes transformation were readily infected by S. hermonthica. There were no significant differences in the number and size of S. hermonthica individuals recovered from either transgenic or wild type roots.

CONCLUSIONS

This rapid, high throughput, transformation technique will advance our understanding of gene function in parasitic plant-host interactions.

The transcription factor CrWRKY1 positively regulates the terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Catharanthus roseus produces a large array of terpenoid indole alkaloids (TIAs) that are an important source of natural or semisynthetic anticancer drugs. The biosynthesis of TIAs is tissue specific and induced by certain phytohormones and fungal elicitors, indicating the involvement of a complex transcriptional control network. However, the transcriptional regulation of the TIA pathway is poorly understood. Here, we describe a C. roseus WRKY transcription factor, CrWRKY1, that is preferentially expressed in roots and induced by the phytohormones jasmonate, gibberellic acid, and ethylene. The overexpression of CrWRKY1 in C. roseus hairy roots up-regulated several key TIA pathway genes, especially Tryptophan Decarboxylase (TDC), as well as the transcriptional repressors ZCT1 (for zinc-finger C. roseus transcription factor 1), ZCT2, and ZCT3. However, CrWRKY1 overexpression repressed the transcriptional activators ORCA2, ORCA3, and CrMYC2. Overexpression of a dominant-repressive form of CrWRKY1, created by fusing the SRDX repressor domain to CrWRKY1, resulted in the down-regulation of TDC and ZCTs but the up-regulation of ORCA3 and CrMYC2. CrWRKY1 bound to the W box elements of the TDC promoter in electrophoretic mobility shift, yeast one-hybrid, and C. roseus protoplast assays. Up-regulation of TDC increased TDC activity, tryptamine concentration, and resistance to 4-methyl tryptophan inhibition of CrWRKY1 hairy roots. Compared with control roots, CrWRKY1 hairy roots accumulated up to 3-fold higher levels of serpentine. The preferential expression of CrWRKY1 in roots and its interaction with transcription factors including ORCA3, CrMYC2, and ZCTs may play a key role in determining the root-specific accumulation of serpentine in C. roseus plants.

Genetic transformation of Bacopa monnieri by wild type strains of Agrobacterium rhizogenes stimulates production of bacopa saponins in transformed calli and plants

We have developed an efficient transformation system for Bacopa monnieri, an important Indian medicinal plant, using Agrobacterium rhizogenes strains LBA 9402 and A4. Transformed roots induced by strain LBA 9402 spontaneously dedifferentiated to callus while excised roots induced by strain A4 spontaneously showed induction of shoot buds within 10 days. PCR and RT-PCR analysis revealed the presence and expression of the rolAB and rolC genes at the transcription level in pRi A4 transformed cultures indicating that the TL-DNA was integrated retained and expressed in the A4-Ri transformed shoots. Transformed calli showed the presence of rolAB or rol A, TR and ags genes. Transformed plants showed morphological features typically seen in transgenic plants produced by A. rhizogenes. Growth and biomass accumulation was significantly higher in the transformed shoots (twofold) and roots (fourfold) than in the non-transformed (WT) plants. In pRi A4-transformed plants, the content of bacopasaponin D, bacopasaponin F, bacopaside II and bacopaside V was enhanced significantly as compared to WT plants of similar age while bacoside A3 and bacopasaponin C content was comparable with that of WT plants. Significant increase in content of five bacopa saponins could be detected in pRi 9402-transformed callus cultures. There is an overall stimulatory effect on accumulation of bacopa saponins in transformed plants and cells of B. monnieri establishing the role of endogenous elicitation by Ri T-DNA of A. rhizogenes.

Silencing of tryptamine biosynthesis for production of nonnatural alkaloids in plant culture

Natural products have long served as both a source and inspiration for pharmaceuticals. Modifying the structure of a natural product often improves the biological activity of the compound. Metabolic engineering strategies to ferment "unnatural" products have been enormously successful in microbial organisms. However, despite the importance of plant derived natural products, metabolic engineering strategies to yield unnatural products from complex, lengthy plant pathways have not been widely explored. Here, we show that RNA mediated suppression of tryptamine biosynthesis in Catharanthus roseus hairy root culture eliminates all production of monoterpene indole alkaloids, a class of natural products derived from two starting substrates, tryptamine and secologanin. To exploit this chemically silent background, we introduced an unnatural tryptamine analog to the production media and demonstrated that the silenced plant culture could produce a variety of novel products derived from this unnatural starting substrate. The novel alkaloids were not contaminated by the presence of the natural alkaloids normally present in C. roseus. Suppression of tryptamine biosynthesis therefore did not appear to adversely affect expression of downstream biosynthetic enzymes. Targeted suppression of substrate biosynthesis therefore appears to be a viable strategy for programming a plant alkaloid pathway to more effectively produce desirable unnatural products. Moreover, although tryptamine is widely found among plants, this silenced line demonstrates that tryptamine does not play an essential role in growth or development in C. roseus root culture. Silencing the biosynthesis of an early starting substrate enhances our ability to harness the rich diversity of plant based natural products.

Agrobacterium rhizogenes-mediated transformation of Superroot-derived Lotus corniculatus plants: a valuable tool for functional genomics

BACKGROUND

Transgenic approaches provide a powerful tool for gene function investigations in plants. However, some legumes are still recalcitrant to current transformation technologies, limiting the extent to which functional genomic studies can be performed on. Superroot of Lotus corniculatus is a continuous root cloning system allowing direct somatic embryogenesis and mass regeneration of plants. Recently, a technique to obtain transgenic L. corniculatus plants from Superroot-derived leaves through A. tumefaciens-mediated transformation was described. However, transformation efficiency was low and it took about six months from gene transfer to PCR identification.

RESULTS

In the present study, we developed an A. rhizogenes-mediated transformation of Superroot-derived L. corniculatus for gene function investigation, combining the efficient A. rhizogenes-mediated transformation and the rapid regeneration system of Superroot. The transformation system using A. rhizogenes K599 harbouring pGFPGUSPlus was improved by validating some parameters which may influence the transformation frequency. Using stem sections with one node as explants, a 2-day pre-culture of explants, infection with K599 at OD(600) = 0.6, and co-cultivation on medium (pH 5.4) at 22 degrees C for 2 days enhanced the transformation frequency significantly. As proof of concept, Superroot-derived L. corniculatus was transformed with a gene from wheat encoding an Na+/H+ antiporter (TaNHX2) using the described system. Transgenic Superroot plants were obtained and had increased salt tolerance, as expected from the expression of TaNHX2.

CONCLUSION

A rapid and efficient tool for gene function investigation in L. corniculatus was developed, combining the simplicity and high efficiency of the Superroot regeneration system and the availability of A. rhizogenes-mediated transformation. This system was improved by validating some parameters influencing the transformation frequency, which could reach 92% based on GUS detection. The combination of the highly efficient transformation and the regeneration system of Superroot provides a valuable tool for functional genomics studies in L. corniculatus.

Regulation and function of root exudates

Root-secreted chemicals mediate multi-partite interactions in the rhizosphere, where plant roots continually respond to and alter their immediate environment. Increasing evidence suggests that root exudates initiate and modulate dialogue between roots and soil microbes. For example, root exudates serve as signals that initiate symbiosis with rhizobia and mycorrhizal fungi. In addition, root exudates maintain and support a highly specific diversity of microbes in the rhizosphere of a given particular plant species, thus suggesting a close evolutionary link. In this review, we focus mainly on compiling the information available on the regulation and mechanisms of root exudation processes, and provide some ideas related to the evolutionary role of root exudates in shaping soil microbial communities.

A reliable protocol for transformation of Catharanthus roseus through Agrobacterium tumefaciens

Proliferation of axillary shoot buds and multiple shoot formation in Catharanthus roseus was obtained in 96 % explants on MS medium (3 % sucrose) containing NAA + BA. 2,4-D induced callusing in both, the nodal as well as in leaf segments. Leaf-derived callus was used for transformation with Agrobacterium tumefaciens LBA4404/pBI-S1. Bacterial cell concentration, duration of co-cultivation and acetosyringone concentration influenced transformation efficiency. Under optimal co-cultivation conditions, 98 % of the explants showed GUS expression. PCR based amplification of the transformed and subsequently selected callus tissue indicated the presence of uidA, Gly I and nptII genes.

Spontaneous plant regeneration and production of secondary metabolites from hairy root cultures of Centaurium erythraea Rafn

We have established an efficient protocol for plant regeneration and production of secondary metabolites in hairy root culture of Centaurium erythraea Rafn. Because the hairy roots and regenerated plants produce bitter secoiridoid glucosides and xanthones similar to the plants in nature, the use of in vitro cultures as an alternative source of their production is feasible. This chapter describes a protocol for the induction of adventitious shoots and transgenic plants from hairy root cultures of C. erythraea and their phytochemical analysis.

Hairy root type plant in vitro systems as sources of bioactive substances

"Hairy root" systems, obtained by transforming plant tissues with the "natural genetic engineer" Agrobacterium rhizogenes, have been known for more than three decades. To date, hairy root cultures have been obtained from more than 100 plant species, including several endangered medicinal plants, affording opportunities to produce important phytochemicals and proteins in eco-friendly conditions. Diverse strategies can be applied to improve the yields of desired metabolites and to produce recombinant proteins. Furthermore, recent advances in bioreactor design and construction allow hairy root-based technologies to be scaled up while maintaining their biosynthetic potential. This review highlights recent progress in the field and outlines future prospects for exploiting the potential utility of hairy root cultures as "chemical factories" for producing bioactive substances.

Promoter analysis of the Catharanthus roseus geraniol 10-hydroxylase gene involved in terpenoid indole alkaloid biosynthesis

Geraniol 10-hydroxylase (G10H) is an important enzyme in the biosynthetic pathway of monoterpenoid alkaloids found in diverse plant species. The Catharanthus roseus G10H controls the first committed step in biosynthesis of terpenoid indole alkaloids (TIA). The C. roseus G10H promoter sequence was isolated by a PCR-based genome walking method. Sequence analysis revealed that the G10H promoter contains several potential eukaryotic regulatory elements involved in regulation of gene expression. The major transcription start site of the promoter was mapped to an adenine 31 bp downstream of the TATA-box. For functional characterization, transcriptional fusions between the G10H promoter fragments with 5' or 3' deletions and the GUS reporter gene were generated and their expressions were analyzed in a tobacco protoplast transient expression assay. Deletion of the promoter down to -318 bp had little effect on GUS activity. However, further deletion of the promoter to position -103 resulted in approximately 5-fold reduction of GUS activity. Gain-of-function experiments revealed the presence of three potential transcriptional enhancers located in regions between -191 and -147, -266 and -188, and -318 and -266, respectively. The G10H promoter was capable of conferring stable GUS expression in transgenic tobacco plants and C. roseus hairy roots. In transgenic tobacco seedlings GUS expression was tissue-specific, restricted to leaf and actively growing cells around the root tip, and not detected in the hypocotyls, root cap and older developing areas of the root. The GUS expression in both transgenic C. roseus hairy roots and tobacco seedlings were responsive to fungal elicitor and methyljasmonate. Compared to other known promoters of TIA pathway genes, the G10H promoter contains unique binding sites for several transcription factors, suggesting that the G10H promoter may be regulated by a different transcriptional cascade.

Spontaneous plant regeneration in transformed roots and calli from Tylophora indica: Changes in morphological phenotype and tylophorine accumulation associated with transformation by Agrobacterium rhizogenes

We examined the effects of genetic transformation by Agrobacterium rhizogenes on the production of tylophorine, a phenanthroindolizidine alkaloid, in the Indian medicinal plant, Tylophora indica. Transformed roots induced by the bacterium grew in axenic culture and produced shoots or embryogenic calli in the absence of hormone treatments. However, hormonal treatment was required to regenerate shoots in root explants of wild type control plants. Transformed plants showed morphological features typically seen in transgenic plants produced by A. rhizogenes, which include, short internodes, small and wrinkled leaves, more branches and numerous plagiotropic roots. Plants regenerated from transformed roots showed increased biomass accumulation (350-510% in the roots and 200-320% in the whole plants) and augmented tylophorine content (20-60%) in the shoots, resulting in a 160-280% increase in tylophorine production in different clones grown in vitro.

Metabolic engineering of cell cultures versus whole plant complexity in production of bioactive monoterpene indole alkaloids: Recent progress related to old dilemma

Monoterpene indole alkaloids (MIAs) are a large class of plant alkaloids with significant pharmacological interest. The sustained production of MIAs at high yields is an important goal in biotechnology. Intensive effort has been expended toward the isolation, cloning, characterization and transgenic modulation of genes involved in MIA biosynthesis and in the control of the expression of these biosynthesis-related genes. At the same time, considerable progress has been made in the detailed description of the subcellular-, cellular-, tissue- and organ-specific expressions of portions of the biosynthetic pathways leading to the production of MIAs, revealing a complex picture of the transport of biosynthetic intermediates among membrane compartments, cells and tissues. The identification of the particular environmental and ontogenetic requirements for maximum alkaloid yield in MIA-producing plants has been useful in improving the supply of bioactive molecules. The search for new bioactive MIAs, particularly in tropical and subtropical regions, is continuously increasing the arsenal for therapeutic, industrially and agriculturally useful molecules. In this review we focus on recent progress in the production of MIAs in transgenic cell cultures and organs (with emphasis on Catharanthus roseus and Rauvolfia serpentina alkaloids), advances in the understanding of in planta spatial-temporal expression of MIA metabolic pathways, and on the identification of factors capable of modulating bioactive alkaloid accumulation in nontransgenic differentiated cultures and plants (with emphasis on new MIAs from Psychotria species). The combined use of metabolic engineering and physiological modulation in transgenic and wild-type plants, although not fully exploited to date, is likely to provide the sustainable and rational supply of bioactive MIAs needed for human well being.

Influence of rol genes in floriculture

Traditionally, new traits have been introduced into ornamental plants through classical breeding. However, genetic engineering now enables specific alterations of single traits in already successful varieties. New or improved varieties of floricultural crops can be obtained by acting on floral traits, such as color, shape or fragrance, on vase life in cut-flower species, and on rooting potential or overall plant morphology. Overexpression of the rol genes of the Ri plasmid of Agrobacterium rhizogenes in plants alters several of the plant's developmental processes and affects their architecture. Both A. rhizogenes- and rol-transgenic plants display the "hairy-root phenotype", although specific differences are found between species and between transgenic lines. In general, these plants show a dwarfed phenotype, reduced apical dominance, smaller, wrinkled leaves, increased rooting, altered flowering and reduced fertility. Among the rol genes, termed rolA, B, C and D, rolC has been the most widely studied because its effects are the most advantageous in terms of improving ornamental and horticultural traits. In addition to the dwarfness and the increase in lateral shoots that lead to a bushy phenotype, rolC-plants display more, smaller flowers, and advanced flowering; surprisingly, these plants may have better rooting capacity and they show almost no undesirable traits. rolD, the least studied among the rol genes, offers promising applications due to its promotion of flowering. Although the biochemical functions of rol genes remain poorly understood, they are useful tools for improving ornamental flowers, as their expression in transgenic plants yields many beneficial traits.

Selection of high ginsenoside producing ginseng hairy root lines using targeted metabolic analysis

To develop an experimental system for studying ginsenoside biosynthesis, we generated thousands of ginseng (Panax ginseng C.A. Meyer) hairy roots, genetically transformed roots induced by Agrobacterium rhizogenes, and analyzed the ginsenosides in the samples. 27 putative ginsenosides were detected in ginseng hairy roots. Quantitative and qualitative variations in the seven major ginsenosides were profiled in 993 ginseng hairy root lines using LC/MS and HPLC-UV. Cluster analysis of metabolic profiling data enabled us to select hairy root lines, which varied significantly in ginsenoside production. We selected hairy root lines producing total ginsenoside contents 4-5 times higher than that of a common hairy root population, as well as lines that varied in the ratio of the protopanaxadiol to protopanaxatriol type ginsenoside. Some of the hairy root lines produce only a single ginsenoside in relatively high amounts. These metabolites represent the end product of gene expression, thus metabolic profiling can give a broad view of the biochemical status or biochemical phenotype of a hairy root line that can be directly linked to gene function.