Agrobacterium-Mediated Transformation of Switchgrass and Inheritance of the Transgenes

Switchgrass (Panicum virgatum L.) has been developed into an important biofuel crop. Embryogenic calli induced from caryopses or inflorescences of the lowland switchgrass cultivar Alamo were used for Agrobacterium-mediated transformation. A chimeric hygromycin phosphotransferase gene (hph) was used as the selectable marker and hygromycin as the selection agent. Embryogenic calli were infected with Agrobacterium tumefaciens strain EHA105. Calli resistant to hygromycin were obtained after 5 to 8 weeks of selection. Soil-grown transgenic switchgrass plants were obtained 4 to 5 months after Agrobacterium infection. The transgenic nature of the regenerated plants was demonstrated by PCR, Southern blot hybridization analysis, and GUS staining. T1 progeny were obtained after reciprocal crosses between transgenic and untransformed control plants. Molecular analyses of the T1 progeny revealed various patterns of segregation. Transgene silencing was observed in the progeny with multiple inserts. Interestingly, reversal of the expression of the silenced transgene was found in segregating progeny with a single insert.