Ethylene plays important roles in plant growth, development and stress responses. Its receptor genes have been studied in dicots such as Arabidopsis, tobacco and tomato. However, no research has been reported for the ethylene receptors from monocots currently. In the present study, we cloned an ethylene receptor gene OSPK2 from rice and found that its encoded protein was divergent from the ethylene receptors from dicots. OSPK2 had a long extension in its N- terminal, followed by three transmembrane segments, a GAF domain, a putative kinase domain and a putative receiver domain. Although most of the domains were conserved, the expected phosphorylation site His and the phosphate receiver Asp have been replaced by Gln and Asn, respectively. This fact indicates that OSPK2 may not function as a histidine kinase in a phosphorelay manner, but rather play roles by other mechanism, probably through Ser/Thr kinase activity. The expression of the OSPK2 gene was investigated by RT-PCR method under different conditions. We found that this gene was apparently induced by wounding and PEG treatment, but not significantly affected by salt and ABA treatments. The differential expression of the OSPK2 gene may reflect its roles in mediating different abiotic stress responses, consistent with our previous studies on tobacco ethylene receptors.
