Transient gus expression studies in sorghum to develop a simple protocol for Agrobacterium mediated genetic transformation

Abstract

Agrobacterium mediated transformation was studied in different explants of sorghum through transient gus expression. Our studies showed that immature embryos and calli derived from immature inflorescences were ideal target tissues for obtaining high gus expression with the construct pDM80S. Since the availability of immature embryos and immature inflorescences is limited to the crop season, in vitro protocols based on mature seed as explant source were tested. A simple, economic and time-saving procedure has been developed using shoot apices from three-day old germinated seedlings as target for Agrobacterium infection. Studies on callus induction and regeneration using different explants of sorghum showed that calli derived from immature inflorescences have high regeneration capacity. Callus induction from mature seeds was poor, while in shoot apex explants callus induction was high, but regeneration was low. Therefore, two alternative methods were developed: (i) recovery of plants through direct root induction from shoot apices and (ii) induction of multiple shoots using 6-benzylaminopurine. Genotype specific response to BAP was observed. In addition, infection of 3 day old shoot apices showed high gus expression in all the three elite lines of sorghum tested. These explants can be infected with Agrobacterium and then used either for multiple shoot induction or for obtaining transformed plants directly after root induction