Abstract
Ethylene influences many processes in Arabidopsis (Arabidopsis thaliana) through the action of five receptor isoforms. We used high-resolution, time-lapse imaging of dark-grown Arabidopsis seedlings to better understand the roles of each isoform in the regulation of growth in air, ethylene-stimulated nutations, and growth recovery after ethylene removal. We found that ETHYLENE RECEPTOR1 (ETR1) is both necessary and sufficient for nutations. Transgene constructs in which the ETR1 promoter was used to drive expression of cDNAs for each of the five receptor isoforms were transferred into etr1-6;etr2-3;ein4-4 triple loss-of-function mutants that have constitutive growth inhibition in air, fail to nutate in ethylene, and take longer to recover a normal growth rate when ethylene is removed. The patterns of rescue show that ETR1, ETR2, and ETHYLENE INSENSITIVE4 (EIN4) have the prominent roles in rapid growth recovery after removal of ethylene whereas ETR1 was the sole isoform that rescued nutations. ETR1 histidine kinase activity and phosphotransfer through the receiver domain are not required to rescue nutations. However, REVERSION TO SENSITIVITY1 modulates ethylene-stimulated nutations but does not modulate the rate of growth recovery after ethylene removal. Several chimeric receptor transgene constructs where domains of EIN4 were swapped into ETR1 were also introduced into the triple mutant. The pattern of phenotype rescue by the chimeric receptors used in this study supports a model where a receptor with a receiver domain is required for normal growth recovery and that nutations specifically require the full-length ETR1 receptor.
Highlights
Ethylene influences many processes in Arabidopsis (Arabidopsis thaliana) through the action of five receptor isoforms
Responses to ethylene in Arabidopsis are mediated by a family of five receptors called ETHYLENE RECEPTOR1 (ETR1), ETR2, ETHYLENE RESPONSE SENSOR1 (ERS1), ERS2, and ETHYLENE INSENSITIVE4 (EIN4; Chang et al, 1993; Hua and Meyerowitz, 1998; Hua et al, 1998; Sakai et al, 1998)
I consists of ETR1 and ERS1 that are capable of His kinase activity whereas subfamily II includes ETR2, EIN4, and ERS2 that have Ser/Thr kinase activity in vitro (Gamble et al, 1998; Moussatche and Klee, 2004)
Summary
Ethylene influences many processes in Arabidopsis (Arabidopsis thaliana) through the action of five receptor isoforms. We have previously used high-resolution, time-lapse imaging of seedlings growing in darkness to examine the role of each receptor isoform (Binder et al, 2004b, 2006) Using this system we obtained evidence that ETR1, ETR2, and EIN4 are important for rapid growth recovery after ethylene removal while ERS1 and ERS2 have little or no role in this phenotype (Binder et al, 2004b). In this study we characterized the receptor and receptor domain requirements underlying growth in air, ethylene-stimulated nutations, and recovery of growth after removal of ethylene and found that these phenotypes have different receptor and receptor domain requirements
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