The present invention relates to isolated nucleic acid molecules encoding a type III--secreted bacterial protein capable of modifying a cell death pathway in a plant cell. One aspect of the present invention involves an isolated nucleic acid molecule having a nucleotide sequence that encodes the HopPtoD2 protein of Pseudomonas syringae pv. syringae DC 3000. Expression vectors, host cells, and transgenic plants which include the DNA molecules of the present invention are also disclosed. The nucleic acid molecules of the present invention can be used to impart disease resistance to a plant and to make a plant hypersusceptible to colonization by nonpathogenic bacteria.