An Efficient Agrobacterium-Mediated Genetic Transformation Using Embryonic Axis in Cotton (Gossypium hirsutum L.)

Agrobacterium-mediated genetic transformation approach allows for introducing novel genes in cotton (Gossypium hirsutum L.). Development of efficient regeneration and transformation protocol is very important for recalcitrant plants like cotton. In the present study, five-day-old germinated mature embryo parts especially embryonic axis, hypocotyl and plumule of cotton 'Lashata' were wounded and inoculated with A. tumefaciens strain GV2260 harbouring plasmid p35S-GUS-INT. The binary plasmid p35S-GUS-INT contains neomycin phosphotransferase II (NPTII) gene driven by nopaline synthase (NOS) promoter and beta-glucuronidase (GUS) gene controlled by cauliflower mosaic virus (CaMV) 35S promoter. After inoculation, explants were co-cultivated in liquid and agar-solidified MS medium for 48 h in dark condition. Agar-solidified co-cultivation medium increased transformation frequency as compared to liquid medium. The putative primary transformants were confirmed with histochemical GUS assay, PCR and RT-PCR. However, comparing the three culture explant, the embryonic axis explants had significant difference with embryonic hypocotyl and plumule explants in terms of number and percentage (%) of GUS, PCR and RT-PCR positive plant. The total transformation efficiency was recorded as 3% with varying GUS expression levels.