Small RNAs Derived from the T-DNA of Agrobacterium rhizogenes in Hairy Roots of Phaseolus vulgaris

Epigenetic control of T-DNA during transgenesis and pathogenesis

Mobile elements known as T-DNAs are transferred from pathogenic Agrobacterium to plants and reprogram the host cell to form hairy roots or tumors. Disarmed nononcogenic T-DNAs are extensively used to deliver transgenes in plant genetic engineering. Such T-DNAs were the first known targets of RNA silencing mechanisms, which detect foreign RNA in plant cells and produce small RNAs that induce transcript degradation. These T-DNAs can also be transcriptionally silenced by the deposition of epigenetic marks such as DNA methylation and the dimethylation of lysine 9 (H3K9me2) in plants. Here, we review the targeting and the roles of RNA silencing and DNA methylation on T-DNAs in transgenic plants as well as during pathogenesis. In addition, we discuss the crosstalk between T-DNAs and genome-wide changes in DNA methylation during pathogenesis. We also cover recently discovered regulatory phenomena, such as T-DNA suppression and RNA silencing-independent and epigenetic-independent mechanisms that can silence T-DNAs. Finally, we discuss the implications of findings on T-DNA silencing for the improvement of plant genetic engineering.

Agropine-type rolA modulates ROS homeostasis in an auxin-dependent manner in rolA-expressing cell cultures of Rubia cordifolia L

MAIN CONCLUSION

Long-term cultured calli may experience a biosynthetic shift due to the IAA-dependent expression of the rolA gene, which also affects ROS metabolism. The "hairy root" syndrome is caused by the root-inducing Ri-plasmid of Rhizobium rhizogenes, also known as Agrobacterium rhizogenes. The Ri-plasmid contains genes known as rol genes or root oncogenic loci, which promote root development. The important implications of the rolA gene from the T-DNA include reduced plant size, resistance to infections, and the activation of specialised metabolism. Nevertheless, rolA does not belong to the plast gene group because its function is still uncertain. Recent investigations have shown two important effects of the rolA gene. First, the production of secondary metabolites has changed in long-term cultivated rolA-transgenic calli of Rubia cordifolia L. Second, the expression of both the rolA and rolB genes has a strong auxin-dependent antagonistic effect on reactive oxygen species (ROS) homeostasis. In this work, we attempted to elucidate two rolA gene phenomena: what caused the secondary metabolism of long-term cultured calli to change? How does the individual expression of the rolA gene affect ROS homeostasis? We analysed SNPs in the 5' untranslated region and coding region of the rolA gene. These mutations do not affect the known essential amino acids of the RolA proteins. Notably, in the promoter of the rolA gene, an ACTTTA motif for auxin-mediated transcription factors was identified. Using two separate cell cultures, we demonstrated the strong auxin dependence of rolA gene expression. The expression of genes involved in ROS metabolism decreased in response to an auxin-mediated increase in rolA gene expression. Two assumptions can be made. The long-term cultivation of calli may cause changes in the hormonal state of the culture over time, which may modulate the action of the RolA protein. Moreover, auxin-dependent expression of the rolA gene led to a decrease in ROS metabolism. It can be assumed that the antagonistic interaction between rolA and rolB prevents strong rolB-induced auxin sensitivity and oxidative bursts to balance the cell state.

Injection-based hairy root induction and plant regeneration techniques in Brassicaceae

BACKGROUND

Hairy roots constitute a valuable tissue culture system for species that are difficult to propagate through conventional seed-based methods. Moreover, the generation of transgenic plants derived from hairy roots can be facilitated by employing carefully designed hormone-containing media.

RESULTS

We initiated hairy root formation in the rare crucifer species Asperuginoides axillaris via an injection-based protocol using the Agrobacterium strain C58C1 harboring a hairy root-inducing (Ri) plasmid and successfully regenerated plants from established hairy root lines. Our study confirms the genetic stability of both hairy roots and their derived regenerants and highlights their utility as a permanent source of mitotic chromosomes for cytogenetic investigations. Additionally, we have developed an effective embryo rescue protocol to circumvent seed dormancy issues in A. axillaris seeds. By using inflorescence primary stems of Arabidopsis thaliana and Cardamine hirsuta as starting material, we also established hairy root lines that were subsequently used for regeneration studies.

CONCLUSION

We developed efficient hairy root transformation and regeneration protocols for various crucifers, namely A. axillaris, A. thaliana, and C. hirsuta. Hairy roots and derived regenerants can serve as a continuous source of plant material for molecular and cytogenetic analyses.

Auxin-dependent regulation of growth via rolB-induced modulation of the ROS metabolism in the long-term cultivated pRiA4-transformed Rubiacordifolia L. calli

Gene transfer from Agrobacterium to plants is the best studied example of horizontal gene transfer (HGT) between prokaryotes and eukaryotes. The rol genes of A. rhizogenes (Rhizobium rhizogenes) provide uncontrolled root growth, or "hairy root" syndrome, the main diagnostic feature. In the present study, we investigated the stable pRiA4-transformed callus culture of Rubia cordifolia L. While untransformed callus cultures need PGRs (plant growth regulators) as an obligatory supplement, pRiA4 calli is able to achieve long-term PGR-free cultivation. For the first time, we described the pRiA4-transformed callus cultures' PGR-dependent ROS status, growth, and specialized metabolism. As we have shown, expression of the rolA and rolB but not the rolC genes is contradictory in a PGR-dependent manner. Moreover, a PGR-free pRiA4 transformed cell line is characterised as more anthraquinone (AQ) productive than an untransformed cell culture. These findings pertain to actual plant biotechnology: it could be the solution to troubles in choosing the best PGR combination for the cultivation of some rare, medicinal, and woody plants; wild-type Ri-plants and tissue cultures may become freed from legal controls on genetically modified organisms in the future. We propose possible PGR-dependent relationships between rolA and rolB as well as ROS signalling targets. The present study highlighted the high importance of the rolA gene in the regulation of combined rol gene effects and the large knowledge gap in rolA action.

Raise up of Scopolamine in Hairy Roots Via Agrobacterium rhizogenes ATCC15834 as Compared with Untransformed Roots in Atropa komarovii

Atropa komarovii generates tropane alkaloids and three other compounds such as hyoscyamine. Racemate atropine and scopolamine (hyoscine) are the main alkaloids with anticholinergic, antispasmodic, and sedative agents. A proficient convention has been reported for the formation of transgenic Atropa komarovii by the use of Agrobacterium rhizogenes. Root culture, by utilizing leaves explants was contaminated by Agrobacterium rhizogenes ATCC 15834, a strain with the paired vector. The hairy roots after contamination for three weeks were specifically shaped from the cut edges of the leaves. The PCR intensification demonstrated that rol B genes of Ri plasmid of Agrobacterium rhizogenes were coordinated and communicated into the genome of the changed hairy roots. Examination of HPLC revealed that hairy roots can produce scopolamine and hyoscyamine and it was appeared that scopolamine content was essentially expanded in changed roots and hyoscyamine was extremely expanded in non-transgenic roots. According to the results, it was perceived that the scopolamine content in hairy roots was raised significantly compared to the control roots. It was evidenced that hairy roots gather a great number of metabolites that have a commercial significance. Thus, later on we can enhance efficiency for example by building up the biosynthetic route overexpression of gene codifying enzymes in the metabolic route for expanding valuable secondary metabolites in the plant cures.

Trends in Symbiont-Induced Host Cellular Differentiation

Bacteria participate in a wide diversity of symbiotic associations with eukaryotic hosts that require precise interactions for bacterial recognition and persistence. Most commonly, host-associated bacteria interfere with host gene expression to modulate the immune response to the infection. However, many of these bacteria also interfere with host cellular differentiation pathways to create a hospitable niche, resulting in the formation of novel cell types, tissues, and organs. In both of these situations, bacterial symbionts must interact with eukaryotic regulatory pathways. Here, we detail what is known about how bacterial symbionts, from pathogens to mutualists, control host cellular differentiation across the central dogma, from epigenetic chromatin modifications, to transcription and mRNA processing, to translation and protein modifications. We identify four main trends from this survey. First, mechanisms for controlling host gene expression appear to evolve from symbionts co-opting cross-talk between host signaling pathways. Second, symbiont regulatory capacity is constrained by the processes that drive reductive genome evolution in host-associated bacteria. Third, the regulatory mechanisms symbionts exhibit correlate with the cost/benefit nature of the association. And, fourth, symbiont mechanisms for interacting with host genetic regulatory elements are not bound by native bacterial capabilities. Using this knowledge, we explore how the ubiquitous intracellular Wolbachia symbiont of arthropods and nematodes may modulate host cellular differentiation to manipulate host reproduction. Our survey of the literature on how infection alters gene expression in Wolbachia and its hosts revealed that, despite their intermediate-sized genomes, different strains appear capable of a wide diversity of regulatory manipulations. Given this and Wolbachia's diversity of phenotypes and eukaryotic-like proteins, we expect that many symbiont-induced host differentiation mechanisms will be discovered in this system.