High-efficiency Agrobacterium rhizogenes-mediated transformation of heat inducible sHSP18.2-GUS in Nicotiana tabacum

Nicotiana hairy roots for recombinant protein expression, where to start? A systematic review

BACKGROUND

Hairy roots are a plant-tissue culture raised by Rhizobium rhizogenes infection (formerly known as Agrobacterium rhizogenes). Nowadays, these roots have been gaining more space in biotechnology due to their benefits for the recombinant expression of valuables proteins; it includes simplified downstream processing, protein rhizosecretion, and scalability in bioreactors. However, due to methodological inconsistency among reports, the tissue platform is still a promising technology.

METHODS AND RESULTS

In the current paper, we propose the first step to overcome this issue through a systematic review of studies that employ Nicotiana hairy roots for recombinant expression. We conducted a qualitative synthesis of 36 out of 387 publications initially selected. Following the PRISMA procedure, all papers were assessed for exclusion and inclusion criteria. Multiple points of root culture were explored, including transformation methods, root growth curve, external additives, and scale-up with bioreactors to determine which approaches performed best and what is still required to achieve a robust protocol.

CONCLUSION

The information presented here may help researchers who want to work with hairy roots in their laboratories trace a successful path to appraisal the literature status.

A comparison of strategies for multiple-gene co-transformation via hairy root induction

Hairy root is a transformed root tissue in which transfer DNA (T-DNA) is inserted in the genome by Agrobacterium rhizogenes. To establish a system for multiple-gene co-transformation in hairy roots, we evaluated four different strategies using A. rhizogenes. The genes gusA and mgfp5 were located in separate plasmids, which were transformed into two different batches of A. rhizogenes (strategy 2AR) or a single batch (strategy 2BV). The two reporter genes were also inserted in one T-DNA (strategy 1TD) or two different T-DNAs (strategy 2TD) in a binary vector. Over 90 % of infected Nicotiana tabacum leaf discs formed hairy roots in all four groups, which was not significantly different from the infection efficiency of wild-type A. rhizogenes. Proportions of co-transformed hairy roots with strategies 2AR, 2BV, 1TD, and 2TD were 65.4, 40.0, 78.6, and 82.1 %, respectively, which indicated that all of the strategies were suitable for co-transformation of multiple genes. High variation in growth rate and heterologous protein expression indicated that further screening is required to identify the clone with the highest productivity. Our results indicated that strategies 1TD and 2TD achieved the highest co-transformation efficiency. Combination with strategy 2AR or 2BV provides additional options for co-transformation of multiple transgenes.

What can we learn from tobacco and other Solanaceae about horizontal DNA transfer?

In eukaryotic organisms, horizontal gene transfer (HGT) is regarded as an important though infrequent source of reticulate evolution. Many confirmed instances of natural HGT involving multicellular eukaryotes come from flowering plants. This review intends to provide a synthesis of present knowledge regarding HGT in higher plants, with an emphasis on tobacco and other species in the Solanaceae family because there are numerous detailed reports concerning natural HGT events, involving various donors, in this family. Moreover, in-depth experimental studies using transgenic tobacco are of great importance for understanding this process. Valuable insights are offered concerning the mechanisms of HGT, the adaptive role and regulation of natural transgenes, and new routes for gene trafficking. With an increasing amount of data on HGT, a synthetic view is beginning to emerge.

Isolation of heat shock-induced Nicotiana tabacum transcription promoters and their potential as a tool for plant research and biotechnology

Transcription promoters of heat shock protein (HSP) genes have been used to control the expression of heterologous proteins in plants and plant cells. To obtain a strong HSP promoter that is functionally active in Nicotiana tabacum BY-2 cells, we set out to identify a promoter of an endogenous gene showing high activation of expression by heat. An N. tabacum BY-2 cell culture was treated for 8 h at 37°C and the cell protein extract analyzed by two-dimensional electrophoresis. A major spot was identified by mass spectrometry as belonging to the small HSP family. The promoter regions and the 5' and 3' untranslated regions of two genes, NtHSP3A and NtHSP3B, with sequences fitting the protein identified were cloned and fused to a hybrid reporter gene coding for β-glucuronidase (GUS) and a yellow fluorescent protein. These constructs were introduced into N. tabacum BY2 cells by Agrobacterium tumefaciens-mediated transformation. Both promoters conferred similar heat-induced GUS expression. In the best heat shock condition, GUS activity was increased 200 fold and reached 285 pmol min(-1) μg protein(-1). Up-scaling in a 4-l bioreactor resulted in similar heat-induced expression. The NtHSP3A promoter was then used to drive the expression of NtPDR1, a plasma membrane transporter belonging to the pleiotropic drug resistance family. No expression was observed at 25°C, while, at 37°C, expression was similar to that obtained using a strong constitutive promoter. These data show that the HSP promoters isolated are useful for high heat-induced expression in N. tabacum BY-2 cells.