Streptothricin resistance as a novel selectable marker for transgenic plant cells

Streptothricins are known as antimicrobial agents produced by Streptomyces spp. Bacterial resistance to streptothricin is mediated by specific enzymes exhibiting an acetyltransferase activity which renders the drug non-toxic for bacteria. The nucleotide sequence of several streptothricin resistance genes from bacteria have been described. Certain cells of eukaryotic parasi tes (such as Ustilago maydis or Leishmania spp.) are sensitive to streptoth ricin and the introduction of the bacterial resistance gene sat2 renders th em resistant. We show that numerous species of plants are sensitive to low concentrations of streptothricin. Moreover, introduction of the bacterial r esistance gene sat3 under the control of the 35S cauliflower mosaic virus p romoter protects these cells from the toxic action of streptothricin. There fore, sat3-mediated streptothricin resistance appears to be a promising sel ective marker for genetic manipulation of plant cells.