**7. Conclusion and future perspectives**

This chapter presents a survey of obtaining and developing transgenic *AtCKX* centaury plants grown *in vitro* and is intended to provide a synthesis of the existing literature data. In addition, recent achievements in the characterisation of transgenic centaury plants and determination as well as application of their secondary metabolite content is reported in details.

Centaury is a medicinal plant species endangered in natural habitat. A successful protocol for its genetic transformation using *A. tumefaciens* to introduce foreign, *AtCKX*, genes is described here. This protocol favours centaury root tips as primary infection explants that can directly regenerate shoots without callus phase. As the *in vitro* regeneration of centaury is possible without the addition of exogenous plant growth regulator(s), *in vitro* culture represents an optimal model for studying metabolic pathways of endogenous phytohormones including CKs without any interferences from other exogenous hormones present in nutrition medium. The first step of a successful genetic transformation of centaury was the establishment of stable transformants with *AtCKX* overexpression and enhanced CKX activity. Molecular, morphometric and developmental characterisation of obtained *AtCKX*-transgenic plants as well as chemical profiling of CK metabolites represented the following steps. The subsequent secondary metabolite analyses showed antibacterial and antifungal activity of transgenic centaury plants that can also be used as potential producers of anti-cancer compounds. Considering that centaury can inhabit saline soils in natural habitats, salinity tolerance of transgenic *AtCKX* centaury plants was investigated as well.

All obtained results were summarized and indicated that transgenic *AtCKX* centaury plants can serve as a suitable material for investigations of numerous physiological and developmental processes that are under endogenous phytohormonal control. Also, further studies of endogenous plant hormone regulations during NaCl-induced stress might represent an useful tool for better understanding the salinity tolerance of non-transformed and CK-deficient transgenic centaury plants grown *in vitro*. Future research will certainly be focused on the identification of centaury candidate genes specifically expressed during the salt stress to understand complex regulatory pathways in response of centaury plants to salinity *in vitro*.

## **Acknowledgements**

This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, contract number 451-03-68/2020- 2114/200007, and by the Czech Science Foundation, project number 19-12262S.
