In legumes, ENOD40 expression is increased upon interaction of plants with rhizobia. Little is known of the expression pattern of ENOD40 during other stages of the plant life cycle. Studies of ENOD40 expression in non-legume development may give an indication of the function of the gene. To investigate the ENOD40 expression pattern during plant development, a fusion between the beta-glucuronidase (GUS) reporter gene and 150 bp of the 5' untranslated region plus 3,000 bp of 5' untranscribed tomato ENOD40 sequence was constructed and introduced into Lycopersicon esculentum Miller. Based on the observed GUS expression patterns in transgenic tomato we speculate that ENOD40 in tomato has a role in counteracting ethylene-provoked responses.