THE ETHYLENE-RECEPTOR FAMILY FROM ARABIDOPSIS - STRUCTURE AND FUNCTION

The gaseous hormone ethylene regulates many aspects of plant growth an d development. Ethylene is perceived by a family of high-affinity rece ptors typified by the ETR1 protein from Arabidopsis. The ETR1 gene cod es for a protein which contains a hydrophobic N-terminal domain that b inds ethylene and a C-terminal domain that is related in sequence to h istidine kinase-response regulator two-component signal transducers fo und in bacteria. A structural model for the ethylene-binding domain is presented in which a Cu(I) ion is coordinated within membrane-spannin g alpha-helices of the hydrophobic domain. It is proposed that binding of ethylene to the transition metal would induce a conformational cha nge in the sensor domain that would be propagated to the cytoplasmic t ransmitter domain of the protein. A total of four additional genes tha t are related in sequence to ETR1 have been identified in Arabidopsis. Specific missense mutations in any one of the five genes leads to eth ylene insensitivity in planta. Models for signal transduction that can account for the genetic dominance of these mutations are discussed.