Agrobacterium-mediated maize transformation: immature embryos versus callus

Transformation with Agrobacterium tumefaciens is the preferred method for delivery of transgenes into a wide range of plant species including maize. Optimized protocols for the Agrobacterium-mediated transformation of freshly isolated immature embryos and embryogenic Type I callus derived from plant seedlings are described. These protocols are suitable for the transformation of a wide variety of corn genotypes including commercial inbred lines. Agrobacterium harboring a binary vector containing the neomycin phosphotransferase (nptII) or the glyphosate resistant 5-enolpyruvylshikimate-3-phosphate (EPSPS) as selectable marker genes and also the green fluorescence protein gene (gfp) have been used. GFP is a visual screening marker which allows tracking of transformation during different selection and regeneration steps. The described protocols provide double digit transformation frequencies and can be routinely used for the production of a large numbers of transgenic plants.