Characterization of Defense-Related Genes Ectopically Expressed in Viroid-lnfected Tomato Plants. Jose Gadea. Instituto de Biologfa Molecular y Celular de Plantas (IBMCP), Universidad Politecnica-Consejo Superior de Investigaciones Cientfficas, Camino de Vera s/n, 46022-Valencia, Spain. Maria Esther Mayda, Vicente Conejero, and Pablo Vera Instituto de Biologfa Molecular y Celular de Plantas (IBMCP), Universidad Politecnica-Consejo Superior de Investigaciones Cientfficas, Camino de Vera s/n, 46022-Valencia, Spain. MPMI 9:409-415. Accepted 16 March 1996. Copyright 1996 The American Phytopathological Society.

Differential hybridization was used to isolate genes induced by viroid infection in tomato plants. Four new cDNA clones encoding a peroxidase, a desaturase-like enzyme, a lipoxygenase, and a proteinase inhibitor, were selected and characterized. All of these genes display a characteristic expression pattern, showing constitutive expression in roots of healthy plants and being ectopically activated in aerial tissues upon viroid infection and ethephon treatment. Possible functions for these genes in the viroid-tomato interaction are proposed. The existence of an integrated program that compiles developmental and defense-related responses is also suggested to explain the characteristic expression pattern detected for these genes as well as for other defense-related genes