Regulation of ethylene-mediated responses at the level of the receptor

The ethylene receptor is currently the best characterized of plant hormone receptors. Mutant and biochemical analyses have revealed much about the mode(s) of action and biological regulation of ethylene responses. The receptors are related to bacterial two-component regulators, which are histidine protein kinases. In both arabidopsis and tomato, a family of genes encodes a structurally divergent set of receptors. While one arabidopsis receptor, ETR1, has been shown to be a functional histidine kinase, the significant structural divergence among the family members makes the actual mode of action of the receptors unclear. Molecular and genetic evidence indicates that quantitative alterations in receptor levels can modify the sensitivity of a plant or tissue to ethylene. However, our current knowledge of receptor gene regulation does not address how a plant regulates differential responsiveness of a tissue to ethylene. (C) 2001 Annals of Botany Company.