## 1 Introduction  
_Catharanthus_ is a perennial tropical medicinal plant belonging to the Family Apocynaceae which comprises eight species, seven endemic to Madagascar (_C. coriaceus_, _C. lanceus_, _C. longifolius_, _C. ovals_, _C. roseus_, _C. scitulus_, _C. trichophyllus_), and one, _C. pusillus_, from India. Specifically, _C. roseus_ is a decorative and curing plant of enormous pharmaceutical interest because it is nothing less than a chemical factory, producing more than 130 different terpenoid indole alkaloids (TIAs), some of which exhibit strong and important pharmacological activities [1]. In fact, vinblastine and vincristine are commercial TIAs used in anticancer chemotherapy, and together with a number of related semi-synthetic compounds, are collectively named the Vinca alkaloids. Currently, vinblastine, vincristine, vinorelbine and vindesine have been used in clinical trials, although only vinblastine, vincristine and vinorelbine have been approved for medical treatment in the United States [2]. Vinflunine, a fluorinated analogue of vinorelbine, has been approved in Europe [3,4]. Vincristine and vinblastine also show a strong antimicrobial activity [5]. In addition, _C. roseus_ also produces ajmalicine and serpentine, which are monoterenoic indole alkaloids used as anti-hypertensive and anti-neuro-inflammatory agents, yohimbine which is mainly used in treatments for erectile dysfunction, and vindolicine used for the development of antidiabetic therapeutics. The large interest in the anticancer compounds vinblastine and vincristine, which derive from the coupling of catharanthine and vindoline, contrasts with the low amounts of these compounds found in the plants, making their extraction a very expensive process. These low levels are mainly associated to the spatial separation of biosynthetic sites where these compounds are produced in the plant and to the high degree of specialization of some leaf cells where the assembly of specific steps of the TIA biosynthetic pathway occurs [6]. In fact, catharanthine is accumulated almost exclusively in the wax exudates on the leaf surface, whereas vindoline is produced in specialized internal leaf cells, suggesting that an involvement of transport processes are needed for their coupling to take place [7]. Recently, an ABC transporter, CrTPT2, whose primary function consists in enhancing the transport and hence, the accumulation of catharanthine in the leaf epidermal surface, has been identified [6]. However, the physical separation of catharanthine and vindoline observed by [PERSON] and [PERSON] [6] is probably a limiting factor in very young leaves, where AVLB was actually shown to be absent [8], but definitely not in developed leaves, where the dimer AVLB was repeatedly reported to be abundant [8, 9, 10, 11, 12]. In fact, [PERSON] _et al._[12] demonstrated that catharanthine, vindoline and AVLB were accumulated in the vacuoles of mesophyll cells by a specific proton antiport system, dependent on the transtonoplast pH gradient generated by V-H\({}^{+}\)-ATPase and V-H\({}^{+}\)-PPase using vacuoles isolated from leaves of adult plants. In addition, researchers have looked for alternative sources and strategies to produce TIAs in high amounts. In fact, the low levels of the TIAs with anticancer activity found in plants have stimulated an intense research effort aiming to obtain _in vitro C. roseus_ cultures with a higher production of these TIAs. Technologically, [PERSON] and [PERSON] showed that although _C. roseus_ cells can be cultivated in bioreactors, the TIA biosynthesis is extremely low, which prevents their industrial production. To increase this production, several approaches were tried [13] using _C. roseus_ cell cultures, being genetic modification or metabolic engineering the most promising biotechnological alternatives for producing these compounds [1].