RESUMO
During the last decade, Agrobacterium-mediated transformation of more than a dozen monocotyledonous plants, including forage and turf grasses, has been achieved. So far, switchgrass is the only warm season grass that has been transformed with A. tumefaciens. We have developed a highly efficient system for transformation of different switchgrass explants utilizing the A. tumefaciens strain AGL1 carrying the binary vector pDM805, containing the phosphinotricin acetyltransferase (bar) and beta-glucoronidase (GUS) (uidA or gus) genes. Transformed cultures were selected in the presence of 10 mg/L bialaphos and the resultant plantlets were treated with the herbicide Basta. The T-DNA delivery frequency was affected by the genotype, explant used, and the presence or absence of acetosyringone during inoculation and cocultivation. The total time required from inoculation to the establishment of plants in soil was 3-4 mo. Stable integration, expression, and inheritance of both transgenes were confirmed by molecular and genetic analyses. Approximately 90% of the tested plants appeared to have only one or two copies of the T-DNA inserts. The transgenes were sexually transmitted through both male and female gametes to the progeny obtained from controlled crosses in the expected segregation ratio of 1:1 according to a chi(2) test at p = 0.05.