BT37 is a crown gall
teratoma incited on tobacco by Agrobacterium tumefaciens containing pTi-T37, a
nopaline-type Ti plasmid. Treatment of this cloned
tumor tissue with
kinetin at 1 mg/liter results in the formation of relatively normal-appearing shoots. These shoots can be induced to root and set viable seed. In contrast to BT37 tissue, the derived tissues are not
phytohormone independent and do not produce
nopaline. The reverted plants, like normal tobacco plants, are susceptible to
infection by A. tumefaciens. This loss of tumorous traits is accompanied by the loss of most of the Ti plasmid sequences (
T-DNA) found in BT37
DNA. Southern blot analysis indicates that the revertant tissues have lost the central portion of the
T-DNA, which contains the "common DNA" sequences, a highly conserved region of the Ti plasmid that has been found to be incorporated into all
tumors studied. Thus, these sequences appear necessary for oncogenicity and
tumor maintenance and their loss is probably directly related to
tumor reversal. The reverted plants as well as the plants obtained from seed, however, do retain sequences homologous to the ends of the
T-DNA present in the parental
teratoma. The persistence of foreign DNA sequences during the process of meiosis and seed formation has important implications for the possibility of the genetic engineering of plants.