Agrobacterium-mediated gene transformation in grain sorghum

The major cereals, rice, wheat, maize, and barley, have been transformed successfully with agronomically useful genes by both biolistic and Agrobacterium-mediated techniques. However, only a limited number of reports on sorghum transformation, all using biolistic protocols, have been reported. In this study, we demonstrated that Agrobacterium -mediated transformation could be used successfully to introduce agronomically useful genes into sorghum. Even though some limitations exist regarding the sorghum inbreds that are amenable to transformation with a specific Agrobacterium strain, the efficiency of transformation appears to be higher than that of biolistic procedures. Further, a majority of the transformants appeared to have a small number of copies of transgenes, which were transmitted to T₁ progeny and expressed stably. Nineteen transgenic plants expressing a rice thaumatin-like protein and three expressing a rice chitinase were obtained with the bar gene as the selectable marker from embryogenic calli of sorghum inbred line C401.; Transformation of sorghum using the Agrobacterium technique has been optimized using the visual marker gene, gfp, in order to establish a reliable and efficient transformation system. GFP was detected in living tissues following transient transfection of sorghum calli. Transient expression was observed shortly after biolistic bombardment. GFP expression could be detected in all three inbreds, Tx430, C401, and Wheatland, using both biolistic and Agrobacterium-mediated transformation. The Agrobacterium strains were tested with different concentrations of a phenolic compound (acetosyringone) for maximal GFP expression. Inbred Tx430 and A. tumefaciens strain EHA105 was most appropriate for gfp gene transformation. Micro-wounding caused by sonication enhanced the bacterial infection for the sorghum calli leading to the formation of larger transformed cell clusters.; T₁ and T₂ progenies of seven segregating transgenic lines expressing the tlp gene were tested for drought tolerance and sorghum stalk rot caused by Fusarium moniliforme under greenhouse conditions. Plants expressing tlp gene at high levels had significantly higher (P < 0.05) relative water content (RWC) and osmotic potential compared to control and non-expressing or lower tlp expressing plants. These plants resist drought stress by controlling plant and water relationship under a water-deficient condition, whereas the control plants were very susceptible. The T₁ plants derived from plant #22 expressing the tlp transgene showed high resistance to stalk rot disease by inhibiting fungal growth around the point of inoculation. The majority of the tlp transgenic plants showed improved resistances to water deficit and Fusarium stalk rot compared to the control plants.