Genetic analysis of ethylene responses in Arabidopsis thaliana

The plant hormone ethylene mediates a number of developmental processes and responses to environmental stress in higher plants. Our research efforts over the last three years have been focused on developing an understanding of the molecular basis of ethylene action in plants. To this end, we have isolated mutants in Arabidopsis thaliana with altered responses to ethylene. One such mutant, designated etr, shows no measurable responses to ethylene and has reduced ethylene binding in leaf tissue indicating that the mutation may directly affect the ethylene receptor. We have genetically mapped the etr mutation and by chromosome walking have isolated an 18 kb fragment of genomic DNA that contains the mutant gene. Sequence analysis of cDNAs which map to the 18 kb fragment has produced a candidate for the ETR gene which codes for a putative transmembrane protein kinase. Sequence analysis indicates a domain composed of 9 copies of a 23 amino acid leucine-rich repeat unit and a domain containing a serine/threonine type protein kinase. These two domains are separated by a single 24 amino acid hydrophobic domain. A model is presented that describes the possible mechanism of action of the protein kinase with respect to ethylene-mediated responses in plants.