Plant Cell Reports (2000) 19 : 1232–1239 Q Springer-Verlag 2000 Communicated by K. Glimelius R. Müller (Y) 7 M. Serek Department of Agricultural Sciences, Horticulture, The Royal Veterinary and Agricultural University, Thorvaldsensvej 57, 1871 Frederiksberg C, Denmark e-mail: renate.muller6agsci.kvl.dk B.M. Stummann Department of Ecology; Genetics and Microbiology, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark PHYSIOLOGY AND BIOCHEMISTRY R. Müller 7 B.M. Stummann 7 M. Serek Characterization of an ethylene receptor family with differential expression in rose (Rosa hybrida L.) flowers Received: 22 December 1999 / Revision received: 22 May 2000 / Accepted: 23 May 2000 Abstract To analyze differences in flower longevity and ethylene sensitivity, we isolated Rosa hybrida gene fragments with sequence similarity to the Arabidopsis thaliana ethylene receptor gene-family. A rose gene (RhETR1) highly similar to AtERS1 had been previously sequenced. Here, we report the isolation of three additional partial rose genes (RhETR2–4) belonging to different sub-groups of ethylene receptor genes. RhETR2 clusters with AtETR1, RhETR4 with AtERS1 and RhETR1, whereas RhETR3 shows high sequence similarity to AtETR2 and AtERS2. Expres- sion analysis of RhETR2 and RhETR3 revealed that they are differentially expressed. RhETR2 is expressed at a constitutive level throughout flower development whereas RhETR3 expression increases in senescing flowers of the cultivar ‘Bronze’ which has a short floral life while it remains at low levels in the long-lasting flowers of the cultivar ‘Vanilla’. Expression of both genes was increased by ABA and ethylene treatment, but transcript abundance differed between rose culti- vars with different postharvest performance. These results indicate that differences in flower life among rose cultivars could be due to differences in receptor levels. Keywords Abscisic acid 7 Ethylene 7 ETR homologues 7 Flower senescence 7 Rosa hybrida Abbreviations ABA Abscisic acid 7 DIG Digoxigenin 7 SSC Standard saline citrate Introduction The plant hormone ethylene plays a central role in physiological and developmental processes, such as germination, growth, flower initiation, senescence of leaves and flowers, organ abscission and fruit ripening (Abeles et al. 1992). Ethylene perception in plant tissue requires specific receptors and a signal transduction pathway to coordinate downstream responses. Progress made in understanding the ethylene perception and signal transduction pathway has mainly been achieved by molecular studies that used the model plant Arabi- dopsis. Ethylene response mutants have been identified by screening for alteration in the so-called triple response, referring to morphological changes of dark- grown seedlings in response to ethylene. The ethylene- insensitive mutants, e.g. ETR1–1 (Bleecker et al. 1988), do not exhibit a triple response. The gene ETR1 encodes a protein with amino acid similarity to bacte- rial two-component sensor response-regulator systems and acts early in the response pathway as an ethylene receptor (Chang et al. 1993; Ecker 1995). ETR1 is likely to be a receptor that transduces the ethylene signal using the phosphotransfer mechanism estab- lished for bacterial sensors and receivers (Parkinson and Kofoid 1992; Chang 1996). The putative histidine kinase domain of ETR1 was expressed in yeast as a fusion protein with glutathione S-transferase and demonstrated to have histidine kinase activity (Gamble et al. 1998). However, recently reported findings indi- cate that histidine kinase activity may not be necessary for an ethylene response, because some receptors lack the histidine within the kinase domain that is predicted to be phosphorylated (Hua et al. 1998; Tieman and Klee 1999). Until now, five members of the putative ethylene receptor gene family in Arabidopsis have been cloned.