Gene Technological Study on Disease Control by the Inactivation of Pathogenic Toxins in Transgenic Plants

Abstract

Advances in plant genetic engineering have allowed to create the transgenic plants resistant to herbicides, insects and viruses by transfer of single dominant gene. Such strategies could be used to achieve plant protection against bacterial and fungal diseases, especially caused by toxin-producing microorganisms. We have been interested in the tobacco wildfire disease caused by Pseudomonas syringae pv. tabaci, which produces a phytotoxic tabtoxin. It is known that tabtoxin has an important role in the development of chlorotic symptoms typical to the wildfire disease. An attempt was made to screen and clone the tabtoxin resistance genes from the wildfire pathogen itself, because some antibiotic-producing microorganisms are possessed of self-resistance genes to protect themselves from their toxic metabolite. We have isolated a tabtoxin resistance gene (ttr) coding for an acetyltransferase, which inactivates tabtoxin by acetylation. The chimeric ttr gene fused to the 35S promoter of cauliflower mosaic virus was inserted on the Ti-vector plasmid for introduction into tobacco cells by Agrobacterium-mediated transformation. The transgenic tobacco plants showed high-specific expression of the ttr gene, and became resistant to tabtoxin treatment. The inactivation of tabtoxin in the transgenic plants also conferred resistance to the bacterial attack of P. syringae pv. tabaci. These results demonstrate a successful approach to create the disease-resistant plants by genetic engineering for detoxification of pathogenic toxins. Also, such a strategy could be widely applied to other diseases caused by pathogenesis-related toxins.