The Agrobacterium rhizogenes rolC-gene-induced somatic embryogenesis and shoot organogenesis in Panax ginseng transformed calluses

Protein profile changes during priming explants to embryogenic response in Coffea canephora: identification of the RPN12 proteasome subunit involved in the protein degradation

Plant somatic embryogenesis encompasses somatic cells switch into embryogenic cells that can later produce somatic embryos with the ability to produce plantlets. Previously, we defined in vitro culture settings for the somatic embryogenesis process of Coffea canephora that comprise adequate plantlets with auxin plus cytokinin followed by cut-leaf explant cultivation with cytokinin, producing embryos with the ability to regenerate plantlets. Here, we confirmed that cultivating cut-leaf explants with cytokinin is sufficient to promote somatic embryos proliferation and the high yield of somatic embryos in the protocol requires adequate plantlets with auxin plus cytokinin. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels reveal auxin-plus cytokinin-dependent regulated proteins in plantlets with up and down abundance. Chitinase A class III, proteins involved in the metabolism and folding of proteins, photosynthesis, antioxidant activity, and chromatin organization were identified. The RPN12 protein, which is a subunit of the proteasome 26S, has an abundance that is not associated with transcript changes, suggesting post-translational regulation.

Biotechnological Advances in Pharmacognosy and In Vitro Manipulation of Pterocarpus marsupium Roxb

Trees are vital resources for economic, environmental, and industrial growth, supporting human life directly or indirectly through a wide variety of therapeutic compounds, commodities, and ecological services. Pterocarpus marsupium Roxb. (Fabaceae) is one of the most valuable multipurpose forest trees in India and Sri Lanka, as it is cultivated for quality wood as well as pharmaceutically bioactive compounds, especially from the stem bark and heartwood. However, propagation of the tree in natural conditions is difficult due to the low percentage of seed germination coupled with overexploitation of this species for its excellent multipurpose properties. This overexploitation has ultimately led to the inclusion of P. marsupium on the list of endangered plant species. However, recent developments in plant biotechnology may offer a solution to the overuse of such valuable species if such advances are accompanied by technology transfer in the developing world. Specifically, techniques in micropropagation, genetic manipulation, DNA barcoding, drug extraction, delivery, and targeting as well as standardization, are of substantial concern. To date, there are no comprehensive and detailed reviews of P. marsupium in terms of biotechnological research developments, specifically pharmacognosy, pharmacology, tissue culture, authentication of genuine species, and basic gene transfer studies. Thus, the present review attempts to present a comprehensive overview of the biotechnological studies centered on this species and some of the recent novel approaches for its genetic improvement.

Using Morphogenic Genes to Improve Recovery and Regeneration of Transgenic Plants

Efficient transformation of numerous important crops remains a challenge, due predominantly to our inability to stimulate growth of transgenic cells capable of producing plants. For years, this difficulty has been partially addressed by tissue culture strategies that improve regeneration either through somatic embryogenesis or meristem formation. Identification of genes involved in these developmental processes, designated here as morphogenic genes, provides useful tools in transformation research. In species from eudicots and cereals to gymnosperms, ectopic overexpression of genes involved in either embryo or meristem development has been used to stimulate growth of transgenic plants. However, many of these genes produce pleiotropic deleterious phenotypes. To mitigate this, research has been focusing on ways to take advantage of growth-stimulating morphogenic genes while later restricting or eliminating their expression in the plant. Methods of controlling ectopic overexpression include the use of transient expression, inducible promoters, tissue-specific promoters, and excision of the morphogenic genes. These methods of controlling morphogenic gene expression have been demonstrated in a variety of important crops. Here, we provide a review that highlights how ectopic overexpression of genes involved in morphogenesis has been used to improve transformation efficiencies, which is facilitating transformation of numerous recalcitrant crops. The use of morphogenic genes may help to alleviate one of the bottlenecks currently slowing progress in plant genome modification.

The Agrobacterium Phenotypic Plasticity (Plast) Genes

The transfer of T-DNA sequences from Agrobacterium to plant cells is a well-understood process of natural genetic engineering. The expression of T-DNA genes in plants leads to tumors, hairy roots, or transgenic plants. The transformed cells multiply and synthesize small molecules, called opines, used by Agrobacteria for their growth. Several T-DNA genes stimulate or influence plant growth. Among these, iaaH and iaaM encode proteins involved in auxin synthesis, whereas ipt encodes a protein involved in cytokinin synthesis. Growth can also be induced or modified by other T-DNA genes, collectively called plast genes (for phenotypic plasticity). The plast genes are defined by their common ancestry and are mostly found on T-DNAs. They can influence plant growth in different ways, but the molecular basis of their morphogenetic activity remains largely unclear. Only some plast genes, such as 6b, rolB, rolC, and orf13, have been studied in detail. Plast genes have a significant potential for applied research and may be used to modify the growth of crop plants. In this review, I summarize the most important findings and models from 30 years of plast gene research and propose some outlooks for the future.

Biosynthesis and biotechnological production of ginsenosides

Medicinal plants are essential for improving human health, and around 75% of the population in developing countries relies mainly on herb-based medicines for health care. As the king of herb plants, ginseng has been used for nearly 5,000 years in the oriental and recently in western medicines. Among the compounds studied in ginseng plants, ginsenosides have been shown to have multiple medical effects such as anti-oxidative, anti-aging, anti-cancer, adaptogenic and other health-improving activities. Ginsenosides belong to a group of triterpene saponins (also called ginseng saponins) that are found almost exclusively in Panax species and accumulated especially in the plant roots. In this review, we update the conserved and diversified pathway/enzyme biosynthesizing ginsenosides which have been presented. Particularly, we highlight recent milestone works on functional characterization of key genes dedicated to the production of ginsenosides, and their application in engineering plants and yeast cells for large-scale production of ginsenosides.

Horizontal gene transfer from Agrobacterium to plants

Most genetic engineering of plants uses Agrobacterium mediated transformation to introduce novel gene content. In nature, insertion of T-DNA in the plant genome and its subsequent transfer via sexual reproduction has been shown in several species in the genera Nicotiana and Linaria. In these natural examples of horizontal gene transfer from Agrobacterium to plants, the T-DNA donor is assumed to be a mikimopine strain of A. rhizogenes. A sequence homologous to the T-DNA of the Ri plasmid of Agrobacterium rhizogenes was found in the genome of untransformed Nicotiana glauca about 30 years ago, and was named "cellular T-DNA" (cT-DNA). It represents an imperfect inverted repeat and contains homologs of several T-DNA oncogenes (NgrolB, NgrolC, NgORF13, NgORF14) and an opine synthesis gene (Ngmis). A similar cT-DNA has also been found in other species of the genus Nicotiana. These presumably ancient homologs of T-DNA genes are still expressed, indicating that they may play a role in the evolution of these plants. Recently T-DNA has been detected and characterized in Linaria vulgaris and L. dalmatica. In Linaria vulgaris the cT-DNA is present in two copies and organized as a tandem imperfect direct repeat, containing LvORF2, LvORF3, LvORF8, LvrolA, LvrolB, LvrolC, LvORF13, LvORF14, and the Lvmis genes. All L. vulgaris and L. dalmatica plants screened contained the same T-DNA oncogenes and the mis gene. Evidence suggests that there were several independent T-DNA integration events into the genomes of these plant genera. We speculate that ancient plants transformed by A. rhizogenes might have acquired a selective advantage in competition with the parental species. Thus, 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 review we focus on the structure and functions of cT-DNA in Linaria and Nicotiana and discuss their possible evolutionary role.

Chromium accumulation and changes in plant growth, selected phenolics and sugars of wild type and genetically modified Nicotiana langsdorffii

Chromium accumulation, dry weight (DW) biomass yield, water content and concentrations of some selected phenolic compounds and carbohydrates were determined in root and shoot of Nicotiana langsdorffii, either wild type (WT) or genetically modified by the insertion of GR and rolC genes, in response to the presence of Cr(VI) in the growth medium. A biomass decrease was observed for WT plants, but not for GR and rolC transformations, in response to Cr(VI) in the growth medium, highlighting a stress situation only in WT line. Shoot chromium concentrations were in all cases about 300 mg kg(-1) DW. In root higher concentrations were found in rolC than in GR and WT (3843, 2600 and 2751 mg kg(-1) DW, respectively). Based on the DW biomass, GR and WT accumulated higher chromium quantities than rolC, both in root (330 and 424 versus 85 μg Cr per plant) and shoot (282 and 275 versus 121 μg Cr per plant). Therefore, GR should be preferred to WT as a promising candidate for chromium phytoremediation. Metabolic shifts of sugars and phenolics were generally observed in response to either gene insertions or exposure to Cr(VI), being the latter more related to the resistance to Cr(VI) than the former.

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.

Horizontal gene transfer from genus agrobacterium to the plant linaria in nature

Genes can be transferred horizontally between prokaryotes and eukaryotes in nature. The best-studied examples occur between Agrobacterium rhizogenes and certain Nicotiana spp. To investigate possible additional cases of horizontal gene transfer in nature between Agrobacterium and plants, a real-time polymerase chain reaction-based approach was employed to screen 127 plant species, belonging to 38 families of Dicotyledones, for the presence of oncogenes homologous to the transfer DNA fragments (T-DNA) from both A. tumefaciens and A. rhizogenes. Among all of the analyzed plant species, we found that only Linaria vulgaris contained sequences homologous to the T-DNA of A. rhizogenes. All screened L. vulgaris plants from various parts of Russia contained the same homologous sequences, including rolB, rolC, ORF13, ORF14, and mis genes. The same opine gene is found in the species of Nicotiana which contain genes of A. rhizogenes. In L. vulgaris, there are two copies of T-DNA organized as a single tandem imperfect direct repeat. The plant DNA sequence of the site of integration shows similarity to a retrotransposon. This site is most likely silent, suggesting that the T-DNA is not expressed. Attempts to demonstrate expression of the T-DNA genes were negative. Our study indicates that the frequency of gene transfer and fixation in the germline from Agrobacterium to plant hosts is rare in the natural environment.

Nucleotide substitutions in rolC and nptII gene sequences during long-term cultivation of Panax ginseng cell cultures

It has been shown previously that the rolC gene from Agrobacterium tumefaciens gene was stably and highly expressed in 15-year-old Panax ginseng transgenic cell cultures. In the present report, we analyze in detail the nucleotide composition of the rolC and nptII (neomycin phosphotransferase) genes, which is the selective marker used for transgenic cell cultures of P. ginseng. It has been established that the nucleotide sequences of the rolC and nptII genes underwent mutagenesis during cultivation. Particularly, 1-4 nucleotide substitutions were found per sequence in the 540 and 798 bp segments of the complete rolC and nptII genes, respectively. Approximately half of these nucleotide substitutions caused changes in the structure of the predicted gene product. In addition, we attempted to determine the rate of accumulation of these changes by comparison of DNA extracted from P. ginseng cell cultures from 1995 to 2007. It was observed that the frequency of nucleotide substitutions for the rolC and nptII genes in 1995 was 1.21 +/- 0.02 per 1,000 nucleotides analyzed, while in 2007, the nucleotide substitutions significantly increased (1.37 +/- 0.07 per 1,000 nucleotides analyzed). Analyzing the nucleotide substitutions, we found that substitution to G or to C nucleotides significantly increased (in 1.9 times) in the rolC and nptII genes compared with P. ginseng actin gene. Finally, the level of nucleotide substitutions in the rolC gene was 1.1-fold higher when compared with the nptII gene. Thus, for the first time, we have experimentally demonstrated the level of nucleotide substitutions in transferred genes in transgenic plant cell cultures.

Suppression of reactive oxygen species and enhanced stress tolerance in Rubia cordifolia cells expressing the rolC oncogene

It is known that expression of the Agrobacterium rhizogenes rolC gene in transformed plant cells causes defense-like reactions, such as increased phytoalexin production and expression of pathogenesis-related proteins. In the present study, we examined whether this phenomenon is associated with increased production of reactive oxygen species (ROS). Single-cell assays based on confocal microscopy and fluorogenic dyes (2,7-dichlorofluorescein diacetate and dihydrorhodamine 123) showed reduced steady-state levels of ROS in rolC-expressing Rubia cordifolia cells as compared with normal cells. Paraquat, a ROS inducer, caused significant ROS elevation in normal cells but had little effect on rolC-transformed cells. Likewise, ROS elevation triggered by a light stress was suppressed in transformed cells. Our results indicate that the rolC gene acts as a ROS suppressor in unstressed cells and its expression prevents stress-induced ROS elevations. We detected a two- to threefold increase in tolerance of rolC-transformed cells to salt, heat, and cold treatments. Simultaneously, rolC-transformed cells maintained permanently active defensive status, as found by measuring isochorismate synthase gene expression and anthraquinone production. Thus, the oncogene provoked multiple effects in which ROS production and phytoalexin production were clearly dissociated.

Functions of rol genes in plant secondary metabolism

For a long time, the Agrobacterium rhizogenes rolA, rolB and rolC oncogenes have been considered to be modulators of plant growth and cell differentiation. A new function of the rol genes in plant-Agrobacterium interaction became apparent with the discovery that these genes are potential activators of secondary metabolism in transformed cells from the Solanaceae, Araliaceae, Rubiaceae, Vitaceae and Rosaceae families. In some cases, the activator effect of individual rol genes is sufficient to overcome the inability of cultured plant cells to produce large amounts of secondary metabolites. Here, I summarize the available evidence that shows that genetic transformation by single Agrobacterium rol genes may be used as a powerful tool to manipulate secondary metabolites in cultured plant cells. Although it is known that the rol genes act via transcriptional activation of defense genes, the mechanism of activation is unclear. In this review, evidence is presented to support the hypothesis that the rol genes mediate uncommon signal transduction pathways in plants.

The rolC gene induces expression of a pathogenesis-related beta-1,3-glucanase in transformed ginseng cells

The Agrobacterium rhizogenes rolC oncogene is capable of stimulating production of secondary metabolites in transformed plant cells that suggest its possible involvement in plant defense reactions. We tested whether the gene could also affect production of pathogenesis-related proteins. Using a well-known group of PR-proteins, such as beta-1,3-glucanases, we observed a 10-fold increase in total beta-1,3-glucanase activity in rolC-transformed Panax ginseng cells compared with normal cells. The increase was due to the production of a salicylic acid-activated beta-1,3-glucanase isoform. We isolated cDNA of the corresponding beta-1,3-glucanase gene (Pg-glu1), which shared 38-60% sequence identity with previously reported sequences of plant beta-1,3-glucanases at the protein level. Levels of Pg-glu1 mRNA transcripts were tightly correlated with expression of the rolC gene. Our data, together with previously reported information, indicate that A. rhizogenes can activate plant defense reactions via expression of T-DNA oncogenes.