Biolistic Transformation

Biolistic transformation (particle bombardment) is based on the delivery of DNA into plant cells by high velocity gold or tungsten particles (Sanford, 1988). Because DNA delivery by particle bombardment is a physical process that does not depend on bacteria, it has become a versatile and effective transformation method for many species, particularly monocot plants (Wang and Ge, 2006). Biolistic transformation of embryogenic cultures has led to the production of transgenic tall fescue plants (Chen et al., 2003, 2004; Cho et al., 2000; Hu et al., 2005; Spangenberg et al., 1995; Wang et al., 2003a, 2001). Morphogenic calli or embryogenic suspension cells have been used as ideal targets for biolistic transformation. The chimeric hygromycin phosphotransferase gene (hph) and phosphinothricin acetyltransferase gene (bar) have been used as selectable markers. The integration and expression of an hph gene in transformed cells results in the ability to phosphorylate hygromycin, thus rendering the cells resistant to this antibiotic. Similarly, the expression of a bar gene in transformed cells results in the acetylation of phosphinothricin (PPT) and renders the cells resistant to this herbicide. The use of antibiotic selection provides an advantage for the transformed cells to proliferate and regenerate into plants, because most of the target cells are not transformed. The construction of a chimeric gene requires a promoter, which directs when and where the gene should be expressed. The commonly used promoters include cauliflower mosaic virus (CaMV) 35S promoter, rice actin promoter, and maize ubiquitin promoter.