Novel aspects and future directions of the roltechnology: improving plants through a non-GMO breeding method

Breeding new traits using natural transformation with the soil bacterium Rhizobium rhizogenes has been successfully applied to induce compact growth in many ornamental plants – and serves as an alternative to application of chemical growth retardants. In the transformation process, transfer-DNA fragments, including root oncogenic loci genes (rol-genes) of the root-inducing (Ri) plasmid are inserted into the plant’s genome during infection. Most interestingly, if unmodified bacterial strains are used, the method is termed non-GMO in several places, e.g., the European Union and Japan. Hence, it is directly applicable to the breeders without any regulatory obstacles on the new cultivar approval. Moreover, interestingly, molecular studies show that several plants, e.g., tobacco, sweet potato and tea, have received the rol-genes from the bacterium through horizontal gene transfer during evolution adding support to the non-GMO label. Recently, novel studies of the belowground rol-transformed phenotype have shown that substantial biomass is allocated there. In the current study, we hereby prove that this also the case in Ri oilseed rape lines. This feature can improve rooting of potted plants, but it also opens for improved drought tolerance and potentially increased nutrient uptake in agricultural crops. Another important aspect is that transformed hairy root cultures can accumulate valuable bioactive compounds to a high extend, e.g., anthocyanins in purple carrots. We now study this further in yew (Taxus baccata) with the aim of investigating the levels of anticarcinogenic compounds, e.g., paclitaxel. Recently, ex vitro hairy roots from taxus seedlings were obtained. For now, it was possible to generate in vitro taxus seedlings and putative hairy roots protruded from the R. rhizogenes inoculation sites. However, persistent remnants of bacteria are consistently present around the putative hairy roots, hence indicating that further post-inoculation procedures are required to generate true hairy roots.