TOLERANCE TO THE FUNGAL PATHOGEN RHIZOCTONIA-SOLANI AG4 OF TRANSGENICTOBACCO EXPRESSING THE MAIZE RIBOSOME-INACTIVATING PROTEIN B-32

The maize b-32 protein is a functional ribosome-inactivating protein ( RIP), inhibiting in vitro translation in the cell-free reticulocyte-de rived system and having specific N-glycosidase activity on 28S rRNA. P revious results indicated that opaque-2 (o2) mutant kernels, lacking b -32, show an increased susceptibility to fungal attack and insect feed ing and that ectopic expression in plants of a barley and a pokeweed R IP leads to increased tolerance to fungal and viral infection. This pr ompted us to test whether b-32 might function as a protectant against pathogens. The b32.66 cDNA clone under the control of the potato wunl gene promoter was introduced into tobacco by Agrobacterium tumefaciens -mediated transformation. Out of 23 kanamycin resistant regenerated sh oots, 16 contained a PCR fragment of the correct size spanning the bou ndary between the promoter used and the coding region of the b-32 gene . Eight independently transformed tobacco lines were randomly chosen f or protein analysis: all of them expressed b-32 protein. The data pres ented indicate that transgenic tobacco plants expressing b-32 show an increased tolerance against infection by the soil-borne fungal pathoge n Rhizoctonia solani Kuhn.