Abstract: An isolated DNA molecule which comprises a DNA promoter sequence which directs root cortex specific transcription of a downstream heterologous DNA segment in a plant cell. A DNA construct which comprises an expression cassette comprising, in the 5' to 3' direction, a promoter of the present invention and a heterologous DNA segment positioned downstream from the promoter and operatively associated therewith. Transformed plants, such as tobacco plants, comprise transformed plant cells containing a heterologous DNA construct comprising an expression cassette as described above.

Abstract: Described herein is a bacterial cell containing a recombinant bacteriophage defense mechanism. The defense mechanism comprises a bacteriophage promoter (e.g., a phage .phi.31 promoter; a T7 promoter) operatively associated with a heterologous DNA encoding a product lethal to the bacterial cell. The bacterial cell is susceptible to infection by a bacteriophage, and the promoter is activated upon the infection of said bacterial cell by that bacteriophage. Bacteria useful in carrying out the invention include both gram negative and gram positive bacteria (e.g., Lactococcus lactis; Escherichia coli); the heterologous DNA may encode an enzyme that degrades nucleic acid (e.g., the products of the LlaI restriction cassette; barnase). Recombinant DNAs useful for making the foregoing cells, cultures prepared from such cells, and fermentation methods carried out with such cells are also disclosed.

Abstract: Recombinant pathogen-resistant plants comprise transformed plant cells, with the transformed plant cells containing a heterologous DNA construct comprising an expression cassette. The construct comprises a promoter, a structural gene positioned downstream from the promoter, and a termination sequence such as the nos terminator positioned downstream from the structural gene. The promoter is one which is activated by a plant pathogen which attacks the plant, such as the RB7 nematode-responsive element. The structural gene encodes a product such as Barnase which is toxic to the plant cells.

Abstract: Disclosed is an isolated DNA molecule comprising a DNA promoter sequence, the RB7 promoter sequence, which is capable of directing root-specific transcription of a downstream structural gene in a plant cell. Also disclosed is a DNA construct comprising an expression cassette, which construct comprises, in the 5' to 3' direction, a promoter of the present invention and a structural gene such a gene coding for an insect toxin positioned downstream from the promoter and operatively associated therewith. Transformed plants, such as tobacco plants, which comprise transformed plant cells which contain a heterologous DNA construct comprising an expression cassette as described above are also disclosed.