Improved Co-transformation of Maize with Vectors Carrying Two Separate T-DNAs Mediated by Agrobacterium tumefaciens

Vectors with two separate T-DNAs for co-transformation mediated by Agrobacterium tumefaciens were tested in maize inbred A188. Although the frequency of transformation during the initial trials was very low, it was remarkably improved by the vector with a phosphinothricin resistance gene (bar) using a modified transformation protocol, which is characterized by the presence of silver nitrate and carbenicillin in the selection medium. The vector with hygromycin resistance gene (hpt) showed low frequency even with the improved protocol, but the use of maize ubiquitin gene promoter elevated the frequency. Both co-transformation and segregation of the progeny free from the selection markers frequencies were reasonably high and similar to those previously observed in rice and tobacco. The two-T-DNA vectors will be a useful tool in molecular biology and biotechnology studies of maize.