A powerful anticancer agent called paclitaxel (Taxol®) has been found to accumulate at low levels in yew (Taxus spp.). Hairy root cultures can be generated by transformation with the bacterium Rhizobium rhizogenes, resulting in hairy roots (HRs) formation. This is an emerging biotechnology tool that can be applied for the production of paclitaxel, which is appealing from both commercial and medicinal standpoints. As a prerequisite, obtaining Taxus seedlings is crucial for transformation with R. rhizogenes to form HRs. Taxus seeds, however, are characterized by a deep dormancy. Embryo rescue methods have therefore been used to assist in breaking the dormancy of Taxus baccata seeds, thus resulting in seedlings. An effective strategy for embryo rescue in the present study (Paper I) was to sterilize the surface of T. baccata seeds collected from the field. There was a 100% germination rate with this strategy, but it is important to keep in mind that not all embryos that germinated grew into fully developed plants. Hence, the present experiment described the growth of seedlings from germinated embryos using an innovative indicator - the fully developed seedling index. Collectively, the results indicated that about 21% of the seedlings eventually grew into fully developed plants. Despite significant efforts were made to overcome the deep seed dormancy of T. baccata and successfully obtain in vitro seedlings, the succeeding transformation experiments using the same protocol that provided effective for Kalanchöe and oilseed rape failed to induce HR formation in the different tissues of these seedlings. Therefore, ex vitro T. baccata seedlings were collected in nature to replace in vitro seedlings for transformation with R. rhizogenes A4 strain (Paper II). With a transformation efficiency of 14.3%, HRs were formed solely from ex vitro seedlings inoculated by a direct inoculation method. In addition to the above studies, additional work has also been conducted. The roles of the individual root oncogenic loci (rol)-genes and open reading frames (ORFs) contained in R. rhizogenes have not been fully understood. Therefore, Kalanchoë blossfeldiana 'Molly' was regenerated following transformation of plant with individual rol-genes / ORFs: rolB, rolC, ORF13a, ORF14 (Paper III and Paper IV). The corollas of the transgenic lines were spherical, and the four petals were fan-shaped. Moreover, the petal edges of transgenic lines were not smooth as wild type, exhibiting curly and irregular edges. A single or low relative gene copy insertion was correlated to higher gene expression in rolB and ΔORF13a lines. Tolerance of detached flowers to 0.5 μl L−1 ethylene was markedly higher for ORF14 with 66% less flower closure at day 3 compared to wild type. Furthermore, subcelluar localization investigated using transient expression in Nicotiana benthamiana showed that rolC and ΔORF13a are soluble and localize in the cytoplasm being able to enter the nucleus.