Ethylene formation and phenotypic analysis of transgenic tobacco plants expressing a bacterial ethylene-forming enzyme.

A bacterial ethylene-forming enzyme (EFE) catalyzes oxygenation of 2-oxoglutarate to produce ethylene and carbon dioxide in contrast to a plant enzyme which uses 1-aminocyclopropane-1-carboxylic acid as a substrate. We constructed several lines of transgenic tobacco plants which expressed an EFE from Pseudomonas syringae pv. phaseolicola PK2. The gene encoding a chimeric protein consisting of EFE and beta-glucuronidase (GUS) was introduced into the tobacco genome using a binary vector which directs expression of the EFE-GUS fusion protein under the control of constitutive promoter of cauliflower mosaic virus 35S RNA. Two lines of transgenic plants produced ethylene at consistently higher rates than the untransformed plant, and their GUS activities were expressed in different tissues. A significant dwarf morphology observed in the transgenic tobacco displaying the highest ethylene production resembled the phenotype of a wild-type plant exposed to excess ethylene. These results demonstrate a potential use of bacterial EFE to supply ethylene as a hormonal signal via an alternative route using an ubiquitous substrate 2-oxoglutarate in plant tissues.