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

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 35STgRTE1 in etr1-7. The RTE1 N terminus is not essential to the etr1-2 function and the expression of rte1(ND49), 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.

Differential Control of Ethylene Responses byGREEN-RIPEandGREEN-RIPE LIKE1Provides Evidence for Distinct Ethylene Signaling Modules in Tomato

“…Furthermore, in tissues where overexpression of either SlGR or SlGRL1 fails to give rise to an ethylene-insensitive phenotype, it is possible that the appropriate target receptor may be absent, present at reduced levels compared with other receptors, or that the response is mediated by receptors that do not require GR/RTE1 family proteins. The latter hypothesis is supported by the observation that the etr1-9/ers1-3 double null mutant of Arabidopsis remains responsive to ethylene, suggesting that certain ethylene responses are therefore likely to be independent of AtRTE1, given that AtRTE1 acts predominantly through the ETR1 receptor (Resnick et al, 2006;Qu et al, 2007;Zhou et al, 2007;Rivarola et al, 2009).…”

“…Genetic analysis indicates that AtRTE1 functions at or upstream of the ethylene receptors but acts independently of the RAN1 copper transporter (Resnick et al, 2006. In support of this hypothesis, AtRTE1 colocalizes with ETR1 in the ER and Golgi membranes and interacts with the N-terminal region of the ETR1 and ERS1 receptors (Zhou et al, 2007;Dong et al, 2008Dong et al, , 2010. Interestingly, mutations at the rte1 locus suppress ethylene insensitivity mediated by a subset of, but not all, etr1 mutant alleles, and reduced ethylene sensitivity mediated through AtRTE1 overexpression is primarily dependent on the presence of ETR1 and not the other ethylene receptors (Resnick et al, 2006Zhou et al, 2007).…”

“…In support of this hypothesis, AtRTE1 colocalizes with ETR1 in the ER and Golgi membranes and interacts with the N-terminal region of the ETR1 and ERS1 receptors (Zhou et al, 2007;Dong et al, 2008Dong et al, , 2010. Interestingly, mutations at the rte1 locus suppress ethylene insensitivity mediated by a subset of, but not all, etr1 mutant alleles, and reduced ethylene sensitivity mediated through AtRTE1 overexpression is primarily dependent on the presence of ETR1 and not the other ethylene receptors (Resnick et al, 2006Zhou et al, 2007). Together, these data suggest that AtRTE1 acts predominantly through the ETR1 receptor, although the exact mechanisms of this interaction are not fully understood.…”

“…S1). The current model of the ethylene signaling pathway would place the localization of the receptors and their interaction with the GR/ RTE1 proteins within the ER, and previous studies have suggested either exclusive localization of AtRTE1, OsRTH1, and OsRTH2 within the Golgi or dual localization within the Golgi and ER (Zhou et al, 2007;Dong et al, 2008;Zhang et al, 2012). These slight discrepancies may be caused by the use of different experimental systems and high-level overexpression of heterologous transgenes that may influence the subcellular localization of proteins.…”

“…SlGR, SlGRL1, and SlGRL2 Are Predominantly Golgi-Localized Proteins Several components of the ethylene signaling pathway are localized within the endomembrane system, and separate studies have reported either dual localization of AtRTE1 within the Golgi and ER membranes or exclusive localization within the Golgi (Chen et al, 2002;Gao et al, 2003;Zhou et al, 2007;Dong et al, 2008;Bisson et al, 2009). To determine the subcellular localization of SlGR and SlGRL1, N-terminal yellow fluorescent protein (YFP) fusions of each protein were constructed and transformed into the etr1-2/rte1-3 double mutant.…”