Catharanthus roseus plant is valued for harboring more than 130 bioactive terpenoid indole alkaloids (TIAs) including the two of its leaf derived bisindole alkaloids-vinblastine and vincristine which are indispensible constituents of antineoplastic drugs used in metastatic malignancy associated with acute lymphoblastic leukaemia's and Hodgkin's/Non-Hodgkin's lymphomas. The extremely low in planta occurrence of TIAs in C. roseus plants resulting in high commercial demand and exorbitant price have brought this herb in focus of an intense scientific scrutiny in last 30 years. Research efforts have so far advanced in two major directions: towards understanding the enzymology and genetic regulation of the concerned metabolic pathway(s) leading to TIAs biosynthesis in plant and, secondly, exploring the possibility of developing cell/tissue culture based platforms for in vitro TIAs production to meet the industry's demand. Designing plants, free from such metabolic constraints, can be a possible approach to enhance the production of plant based medicines. This subject of plant metabolic engineering is gaining lot of attention these days. Pathway manipulation using the modern tools of genetic engineering to over-express a limiting enzyme or to suppress the expression of an enzyme using a shared substrate of a branched pathway are attractive options of metabolic engineering for diverting the metabolic flux towards the synthesis of a desired end product. Knowledge, thus gained, indicates that TIAs biogenetic route is characterized by extensive metabolic cross-talk and shuttling of at least 35 intermediates synthesized via 30 enzymatic reactions occurring in four different types of tissues (epidermis, internal phloem parenchyma, idioblasts and leticifers) and five different sub-cellular compartments (cytosol, vacuole, thyllakoid membrane, nucleus and endoplasmic reticulum). The complexity is further compounded by extremely high level of recalcitrancy of C. roseus plant for regeneration and Agrobacterium- mediated genetic transformation for pathway engineering. As a consequence, all genetic modulation efforts so far made in C. roseus are confined to cell suspension and transformed hairy root cultures that lack the required level of cyto- and tissue- differentiation essential for the expression of entire TIAs pathway genes and enzymes. A perusal of published work in C. roseus clearly suggests that inspite of several pathway manipulation/engineering attempts, the level of TIAs production in cell/tissue/hairy root cultures of this herb could never be enhanced to the level of expectations. The enzymatic, developmental and environmental rigidity/complexi- ties associated with the biosynthetic pathway of these alkaloids have often been cited as possible reasons for these disappointing outcomes Therefore, three major areas of investigation are in focused attention of Catharanthus researchers' the world over are: (1) how to select or design the starting cells or tissue(s) to realize the full potential of applying metabolic engineering tools for up-regulating the TIAs pathway in them; (2) how to overcome the strong recalcitrancy of Catharanthus plant tissues for de novo organogenesis and in vitro plant regeneration for whole plant-level expression of a transgene coding either for a limiting pathway enzyme or a transcription factor that can control the global expression of several pathway genes and, (3) how to overcome the inability of non-differentiated cell cultures to execute those pathway steps that are expressed only in specialized tissues/cells of C. roseus plants. Various biotechnological approaches and generation of novel tissue types have been discussed in the present chapter for the modulation and increased TIAs flux in C. Roseus.

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