GERMLINE TRANSFORMATION OF MAIZE FOLLOWING MANIPULATION OF CHIMERIC SHOOT MERISTEMS

Genetic transformation of maize has been limited to a small number of genotypes that form embryogenic tissue in culture. We have investigate d whether cells in the developing shoot meristem of immature zygotic e mbryos might provide an alternative, more universal target for product ion of transformed maize plants. Following DNA delivery mediated by mi croprojectile bombardment, immature embryos developed into chimeric pl ants with transgenic sectors containing an antibiotic resistance marke r and the B-glucuronidase (GUS) gene at a high frequency. Because the majority of transgenic sectors were restricted in size, the probabilit y of a transformation event contributing to the germline without furth er manipulation was low. To enlarge the transgenic sectors and increas e the likelihood of germline transmission, the apical meristems of ger minated plants were excised and cultured on cytokinin-containing mediu m with a selective agent. Transformed sectors were visualized by their non-bleached phenotype or by staining with a GUS histochemical stain. Hormonally-induced shoot multiplication produced plants with sectors that had a greater chance of contributing to the germline. Transmissio n to progeny was demonstrated both by transgene expression and by Sout hern analysis. This method has been used successfully with genotypes t hat include a sweet corn hybrid and an elite field corn inbred.