Genetic and morphological stability of six-year-old transgenic Tylophora indica plants

Neoteric trends in tissue culture-mediated biotechnology of Indian ipecac [Tylophora indica (Burm. f.) Merrill]

Tylophora indica (Burm. f.) Merrill, an ethno-pharmacologically important perennial climber of Asclepiadaceae, is commonly known as Antamul or Indian ipecac. It is essentially accredited for its medicinal properties owing to its wide range of alkaloids in the form of bioactive secondary metabolites, such as tylophorine, tylophorinine, and tylophorinidine. Accelerated mass propagation of Tylophora is challenging because of its reduced seed germination frequency that consequently headed the pursuit for efficient protocols on in vitro propagation for the large-scale regeneration, conservation as well as sustainable supply of quality propagules. Ample tissue culture-mediated biotechnological investigations have been carried out on this medicinal plant till date and several micropropagation protocols have been standardized as well. The present review compares between several typical methods as well as factors, involving on direct and indirect organogenesis of Tylophora along with various up-to-date and modified techniques such as somatic embryogenesis, protoplast culture, synthetic seed production, genetic transformation, and in vitro interventions for the secondary metabolite production that have been reported in last two decades. This compilation will allow assessing the achievements and trends of Tylophora research so far, as well as will advance the research more rapidly, since many aspects, basic and applied, have yet to be explored.

Micropropagation and genetic transformation of Tylophora indica (Burm. f.) Merr.: a review

This review provides an in-depth and comprehensive overview of the in vitro culture of Tylophora species, which have medicinal properties. Tylophora indica (Burm. f.) Merr. is a climbing perennial vine with medicinal properties. The tissue culture and genetic transformation of T. indica, which has been extensively studied, is reviewed. Micropropagation using nodal explants has been reported in 25 % of all publications. Leaf explants from field-grown plants has been the explant of choice of independent research groups, which reported direct and callus-mediated organogenesis as well as callus-mediated somatic embryogenesis. Protoplast-mediated regeneration and callus-mediated shoot organogenesis has also been reported from stem explants, and to a lesser degree from root explants of micropropagated plants in vitro. Recent studies that used HPLC confirmed the potential of micropropagated plants to synthesize the major T. indica alkaloid tylophorine prior to and after transfer to field conditions. The genetic integrity of callus-regenerated plants was confirmed by RAPD in a few reports. Tissue culture is an essential base for genetic transformation studies. Hairy roots and transgenic T. indica plants have been shown to accumulate tylophorine suggesting that in vitro biology and transgenic methods are viable ways of clonally producing valuable germplasm and mass producing compounds of commercial value. Further studies that investigate the factors affecting the biosynthesis of Tylophora alkaloids and other secondary metabolites need to be conducted using non-transformed as well as transformed cell and organ cultures.

The Fate of Integrated Ri T-DNA rol Genes during Regeneration via Somatic Embryogenesis in Tylophora indica

The fate of integrated Ri T-DNA rol genes during regeneration via indirect somatic embryogenesis and stability of its effect on morphology and tylophorine content of Ri-transformed plants have been studied in Tylophora indica. Integration and expression of Ri T-DNA genes in transformed embryogenic callus lines derived from transformed root lines, 300 Ri-transformed somatic embryos, and 23 Ri-transformed plant lines were analysed. Fifty root lines studied showed integration and expression of four rol genes of TL-DNA. Spontaneous regeneration via indirect somatic embryogenesis was obtained from root lines that were TL+/TR−. Stable integration and expression of rol genes were observed in root lines, embryogenic callus lines, and the spontaneously induced somatic embryos. Nineteen out of the 23 Ri-transformed plant lines and their clones showed phenotypic and genetic stability over the period of 3 years. Four Ri-transformed plants were morphologically similar to nontransformed plants but showed variation with the integration and expression of the rolA gene and absence of other rol genes. Variant Ri-transformed plant line A428#1-V showed highest tylophorine content (2.93±0.03 mg gDW−1) among plant lines studied. The effects of T-DNA genes on growth, morphology, and tylophorine content of the Ri-transformed plants were stable in the long term culture.