efficient plant regeneration and Agrobacterium-mediated genetic transformation of Tagetes erecta

Tagetes erecta, L. an asteraceous plant of industrial and medicinal value, contains important compounds like pyrethrins, thiophenes and lutein, possessing immense potential for insecticidal, nematicidal and nutraceutical activities. Considering the importance and demand for these natural compounds, genetic manipulation of this crop for better productivity of secondary metabolites holds great significance. A rapid and reproducible direct regeneration and genetic transformation system is the prerequisite for genetic manipulation of any crop. This paper elucidates the establishment of an efficient direct regeneration and transformation protocol of T. erecta using Agrobacterium tumefaciens. Investigation of the effects of different types of explants (Hypocotyls, cotyledonary leaves, rachis and leaf sections) and different BAP and GA₃ combinations on the regeneration frequency of T. erecta suggested that the best regeneration frequency (66 %) with an average of 5.08 ± 0.09 shoot buds/explant was observed from hypocotyl explants cultured on media containing 1.5 mg/l BAP and 5 mg/l GA₃. The transformation protocol was established using A. tumefaciens strain LBA4404, containing the binary vector pBI121, along with the gusA reporter gene with intron under the transcriptional control of the Cauliflower Mosaic Virus (CaMV) 35S promoter and the neomycin phosphotransferase II (nptII) gene as a kanamycin-resistant plant-selectable marker. Various parameters like optimization of kanamycin concentration (200 mg/l) for selection, standardization of cocultivation time (45 min) and acetosyringone concentration (150 μM) for obtaining higher transformation frequency were established using hypocotyl explants. The selected putative transgenic shoots were subsequently rooted on the Murashige and Skoog medium and transferred to the green house successfully. The plants were characterised by analysing the gus expression, amplification of 600 bp npt II fragment and Southern blot hybridization using the PCR-amplified gusA fragment as probe. The standardised protocol established during the study will open new vistas for genetic manipulation and introduction of desired genes for genetic improvement of T. erecta.