RTE1 Is a Golgi-Associated and ETR1-Dependent Negative Regulator of Ethylene Responses

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Abstract
Arabidopsis (Arabidopsis thaliana) RTE1 encodes a membrane protein and negatively regulates ethylene responses. Genetic and transformation studies suggest that the function of the wild-type RTE1 is primarily dependent on ETR1 and can be independent on the other receptors. Ethylene insensitivity caused by the overexpression of RTE1 is largely masked by the etr1-7 mutation, but not by any other receptor mutations. The wild-type ETR1 N terminus is sufficient to the activation of the RTE1 function and the ectopic expression of etr1(1–349) restored ethylene insensitivity conferred by 35S∷gRTE1 in etr1-7. The RTE1 N terminus is not essential to the etr1-2 function and the expression of rte1(NΔ49), which has an N-terminal deletion of 49 amino acid residues, restored ethylene insensitivity in etr1-2 rte1-2. The ectopic expression of GREEN FLUORESCENT PROTEIN (GFP)-RTE1 conferred ethylene insensitivity in wild type and the GFP fusion displayed fast movement within the cytoplasm. The GFP-RTE1 and EYFP-NAG proteins colocalized and the Brefeldin A treatment caused aggregation of GFP-RTE1, suggesting RTE1 is a Golgi-associated protein. Our results suggest specificity of the RTE1 function to ETR1 and that endomembranes may play a role in the ethylene signal transduction.