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 mod e(s) of action and biological regulation of ethylene responses. The recepto rs are related to bacterial two-component regulators, which are histidine p rotein kinases. In both arabidopsis and tomato, a family of genes encodes a structurally divergent set of receptors. While one arabidopsis receptor, E TR1, has been shown to be a functional histidine kinase, the significant st ructural divergence among the family members makes the actual mode of actio n of the receptors unclear. Molecular and genetic evidence indicates that q uantitative alterations in receptor levels can modify the sensitivity of a plant or tissue to ethylene. However, our current knowledge of receptor gen e regulation does not address how a plant regulates differential responsive ness of a tissue to ethylene. (C) 2001 Annals of Botany Company.