Summary
Ethylene evolved during compatible or susceptible disease interactions may hasten and/or worsen disease symptom development; if so, the prevention of disease-response
ethylene should reduce disease symptoms. We have examined the effects of reduced
ethylene synthesis on Verticillium wilt (causal organism, Verticillium dahliae) of tomato by transforming tomato with
ACC deaminase, which cleaves ACC, the immediate biosynthetic precursor of
ethylene in plants. Three promoters were used to express
ACC deaminase in the plant: (i) CaMV 35S (constitutive expression); (ii) rolD (limits expression specifically to the site of Verticillium
infection, i.e. the roots); and (iii) prb-1b (limits expression to certain environmental cues, e.g. disease
infection). Significant reductions in the symptoms of Verticillium wilt were obtained for rolD- and prb-1b-, but not for 35S-transformants. The pathogen was detected in stem sections of plants with reduced symptoms, suggesting that reduced
ethylene synthesis results in increased disease tolerance. The effective control of formerly recalcitrant diseases such as Verticillium wilt may thus be obtained by preventing disease-related
ethylene production via the tissue-specific expression of
ACC deaminase.