Co-transformation of grapevine somatic embryos to produce transgenic plants free of marker genes.

A cotransformation system using somatic embryos was developed to produce grapevines free of selectable marker genes. This was achieved by transforming Vitis vinifera L. "Thompson Seedless" somatic embryos with a mixture of two Agrobacterium strains. The first strain contained a binary plasmid with an egfp gene of interest between the T-DNA borders. The second strain harbored the neomycin phosphotransferase (nptII) gene for positive selection and the cytosine deaminase (codA) gene for negative selection, linked together by a bidirectional dual promoter complex. Our technique included a short positive selection phase of cotransformed somatic embryos on liquid medium containing 100 mg/L kanamycin before subjecting cultures to prolonged negative selection on medium containing 250 mg/L 5-fluorocytosine.