Analysis of Arabidopsis cDNA that shows homology to the tomato E8 cDNA.

The negative regulatory protein of ethylene synthesis in ripening tomato fruit, E8, is structurally related to the enzyme that catalyzes the last step in ethylene synthesis, 1-aminocyclopropane-1-carboxylate (ACC) oxidase, and to a large family of 2-oxoglutarate-dependent dioxygenases (2-ODD). A cDNA with structural homology to the tomato E8 was isolated from a cDNA library of Arabidopsis thaliana. Sequence analysis showed that this cDNA, 2A6, encodes a protein of 361 amino acids. Southern blot analysis indicated that the corresponding gene is unique in the Arabidopsis genome. The level of the 2A6 transcript was not increased by ethylene in siliques of Arabidopsis, as was E8 in tomato fruits, and was also expressed in etiolated seedlings, leaves, stems and flowers. The 2A6 protein shows three domains that are highly conserved among E8, ACC oxidases, and 2-ODDs.