Dominant Gain-Of-Function Mutations In Transmembrane Domain Iii Of Ers1 And Etr1 Suggest A Novel Role For This Domain In Regulating The Magnitude Of Ethylene Response In Arabidopsis

Prior work resulted in identification of an Arabidopsis mutant, eer5-1, with extreme ethylene response in conjunction with failure to induce a subset of ethylene-responsive genes, including AtEBP. EER5, which is a TREX-2 homolog that is part of a nucleoporin complex, functions as part of a cryptic aspect of the ethylene signaling pathway that is required for regulating the magnitude of ethylene response.A suppressor mutagenesis screen was carried out to identify second site mutations that could restore the growth of ethylene-treated eer5-1 to wild-type levels.A dominant gain-of-function mutation in the ethylene receptor ETHYLENE RESPONSE SENSOR 1 (ERS1) was identified, with the ers1-4 mutation being located in transmembrane domain III at a point nearly equivalent to the previously described etr1-2 mutation in the other Arabidopsis subfamily I ethylene receptor, ETHYLENE RESPONSE 1 (ETR1). Although both ers1-4 and etr1-2 partially suppress the ethylene hypersensitivity of eer5-1 and are at least in part REVERSION TO ETHYLENE SENSITIVITY 1 (RTE1)-dependent, ers1-4 was additionally found to restore the expression of AtEBP in ers1-4; eer5-1 etiolated seedlings after ethylene treatment in an EIN3-dependent manner.Our work indicates that ERS1-regulated expression of a subset of ethylene-responsive genes is related to controlling the magnitude of ethylene response, with hyperinduction of these genes correlated with reduced ethylene-dependent growth inhibition.