We will develop an optimized transformation system with Agrobacterium to provide marker-free transgene plants. Genetically engineered plants that lack antibiotic or herbicide resistance genes are free of concerns about health and environmental effects that might arise from the use of these marker genes. Moreover, with each new transgene added, a new selectable marker must be used. This proposal will allow development of transgenic plants lacking marker genes and other vector sequences. The marker and transgene contained on two different T-DNAs, each in a different Agrobacterium strain, are introduced into the cell in a process that selects for a co- transformation event. Segregation in the progeny results in recovery of marker-free transgenic plants. Technology obtained in Phase I using Arabidopsis will be transferred to crop plants in Phase II.National Institute of General Medical Sciences (NIGMS)