Heritable transformation of tobacco by Agrobacterium-mediated transfer of the Streptomyces-derived herbicide resistance gene bar

Abstract

Thebar gene of Streptomyces hygroscopicus encodes an enzyme that detoxifies the herbicide Basta. We have transferred the Streptotnyces-derived bar gene to tobacco through the Agrobacterium tumefaciens gene delivery system. Expression ofbar was driven by two different promoters, TR2' or CaMV 35S, in two DNA constructs. TR2' is a weak promoter in tobacco. CaMV 35S is, on the other hand, a strong promoter in tobacco, and transformation using the CaMV 35S promoter construct yielded Basta-resistant transgenic plants. Out of the over one hundred transformants obtained, most could be grown to maturity. Four of these were characterized by genetic and molecular methods. Subsequently, one of the four plants was not resistant and did not show presence ofbar DNA. The remaining three plants contained one or more copies ofbar DNA at one or two loci. Segregation data were consistent with this observation: we obtained ratios of either 3:1 (single locus) or 15:1 (two loci) Basta-resistant:Basta-sensitive in the F2 generation. Field-grown plants showed resistance to Basta up to a level of 4000 g of active ingredient per hectare.