The Ri-technology: improving horticultural plants for the European Society

Breeding through natural transformation with the soil bacterium Rhizobium rhizogenes successfully generated compact growth in many ornamental plants – and serve as a bio-sustainable alternative to application of chemical growth retardants. In the transformation process, transfer-DNA fragments of the root-inducing (Ri) plasmid including root oncogenic loci genes (rol-genes) are inserted into the plant’s genome during infection, thus termed as Ri-technology. With particular interest for the European Society is that this method is labeled non-GMO when unmodified bacterial strains are solely used and hence directly applicable to European breeders. Interestingly, this is supported by evolutionary studies where several plants, e.g., tobacco, sweet potato, tea and blueberries have been shown to carry intrinsic Ri genes from the bacterium through horizontal gene transfer during evolution. Recently, novel studies on the belowground phenotype of plants, naturally transformed with Rhizobium rhizogenes e.g., Kalanchoë have shown that substantial biomass is allocated to the root systems. This feature indicates improved rooting of potted plants, but it also opens up for improved drought tolerance and potentially increased nutrient uptake in agricultural crops e.g., oilseed rape. This study targets the effects of polyethene-glycol 6000 (PEG6000) in hydroponic solutions growing wild plant species from three different genera: Linaria, Nicotiana and Veronica using species with and without intrinsic Ri genes. Moreover, antioxidant gene expression was investigated in Ri lines of oilseed rape. In conclusion, wild species from the Linaria, Nicotiana and Veronica genera tolerated PEG up to 10% for ca. 7-10 days. Furthermore, in Ri oilseed rape lines, a strong upregulation of BnSD2 was found suggesting a pivotal role in enhancing antioxidant capacity under osmotic stress conditions.