Selectable marker genes are essential for the efficient selection of transgenic plants. Heterologous genes used as markers typically encode enzymes that neutralize a toxic compound, allowing for positive selection of plants containing the marker. We report on the efficacy of a novel marker gene system that exploits the varying phytotoxicity of D-amino acids and their oxidative deamination products. Our investigation of a putative DAAO gene from Schizosaccharomyces pombe reveals sufficient oxidative deaminase activity to confer D-alanine and D-serine tolerance to transgenic Arabidopsis thaliana plants carrying the heterologous spDAAO gene. We have demonstrated that the spDAAO, when used in conjunction with D-alanine, allows for the positive selection of primary transformants at levels comparable to hygromycin. Additionally, our selection scheme carries the potential for negative selection in the presence of different selection substrates, such as D-valine or D-isoleucine. This attribute, known as conditional selection would provide particular utility to applications involving site-specific recombinase mediated marker gene removal.M.S.Includes bibliographical references (p. 42-46)
