A Rare Event of Agrobacterium rhizogenes-assisted Genetic Transformation of 'Silk' Banana (genotype-AAB)

Genetic transformations in monocots are achieved with low frequencies with Agrobacterium tumefaciens, often in conjunction with biolistic methods. However, we report here for the first time, the use of A. rhizogenes harbouring a binary vector and utilization of shoot bud explants, instead of embryogenic cultures, while also establishing that intervening hairy root stage can be bypassed. A. rhizogenes strain A4 harbouring plasmid pCAMBIA 1301 with an intron uidA reporter and hygromycin phosphotransferase (hptII) marker gene under the control of CaMV35S promoter was used for sonication-assisted transformation of shoot bud explants of an endemic banana cv. Nanjanagudu Rasabale (NR) grouped under genotype AAB. Transformation frequency up to 2.4% was obtained depending on the medium used. The use of hygromycin in the multiple shoot induction medium allowed the selection of transgenics having Ri T-DNA along with the T-DNA from the pCAMBIA 1301 binary vector. The putative transformants were positive for the expression of the uidA gene. PCR and Southern blot analysis confirmed the independent, transgenic nature of transformants and indicated single and multiple locus integrations.