Ethylene receptors and molecular mechanism of ethylene sensitivity in plants

A short post-harvest longevity remains a major limiting factor for many crops. Separation from plant leads quickly to ripening of fruits and senescence of flowers. In many species, ripening and senescence are ethyleneregulated. Thus, attempts have been made to retard the post-harvest processes by applying chemicals that inhibit ethylene synthesis. The long-term solution will probably be based on genetically modified plants with genes that either suppress synthesis or reduce sensitivity to ethylene. Several genes that confer ethylene insensitivity are known, e.g. tomato Nr and dominant mutants of Arabidopsis ethylene receptor sensor genes, ETR and ERS. Transformation with the etr1-1 allele delays fruit ripening, flower senescence and flower abscission of tomato and petunia. After the successful isolation of the Arabidopsis ethylene receptor gene ETR1, many ETR1-like genes has been isolated, based on sequence similarity and structural features, from various plant species. Characterization of ethylene receptor genes provides clues to understand how plants regulate their ethylene sensitivity. Therefore, an alteration of ethylene action is a valuable target for the genetic engineering of crops. Manipulation of ethylene biosynthesis or perception allows us to modulate these processes and thereby create plants with more robust and desirable traits, giving us a glimpse into the role of ethylene in the plant. The recent progress in genetic and protein analysis of ethylene receptors is summarized in this review. The possible strategies for altering the ethylene sensitivity of plants using ethylene receptor genes are also discussed.