Selection of npUl Transgenic Sweetpotato Plants Using G418 and Paromomycin

We have used two aminoglycosides, G418 and paromomycin, to develop a reliable selection system for nptll transgenic sweetpotato (Ipomoea batatas (L.) Lain.). Embryogenic calli derived from shoot apical meristems were bombarded with gold particles coated with pCAMBIA2301, which contained the nptll and gusA genes. When compared on a kill curve that was based on calli proliferation and cell viability, G4~8-selection proved to be more efficient and had fewer escapes than kanamycin. These bombarded explants were then selected on G418-containing media. The total time required from bombardment to plant establishment in soil was seven to nine months. Multiple copies of the transgene were integrated into the sweetpotato genome. Northern analysis confirmed transgene expression in the regenerated plants, and a paromomycin assay demonstrated that the npUl gene was functionally expressed in transformed sweetpotato. These molecular analyses and assays all showed that selection with G418 and paromomycin is reliable. So far, we have produced 69 transgenic events with this system, at a transformation frequency of approx. 1.1%. That efficiency is based on the number of transgenic plants obtained and the amount of calli bombarded. Thus, this selection method that combines G41a with paromomycin is now available for selecting npUl transgenic sweetpolato.