A two-component gene (NTHK1) encoding a putative ethylene-receptor homolog is both developmentally and stress regulated in tobacco

The full-length of a two-component gene NTHK1 (Nicotiana tabacum histidine kinase-l) was isolated from tobacco (N. tabacum var. Xanthi) using a previously obtained NTHK1 cDNA fragment as a probe. Sequence analysis revealed that NTHK1 shared high homology with LeETR4 from tomato and encoded an ethylene-receptor homolog. The predicted NTHK1 protein had a putative signal peptide, three transmembrane domains, a histidine kinase domain and a receiver domain. The putative autophosphorylation site at His378 and the phosphate receiver site at Asp689 were also identified. By using the in situ hybridization technique, NTHK1 mRNA was detected during flower organ development. It is also highly expressed in the processes of pollen formation and embryo development. The expression of NTHK1 in response to wounding and other stresses was investigated using competitive RT-PCR. The results demonstrated that NTHK1 was inducible upon wounding (cutting). Floating of the cut leaf pieces in 0.5 x MS, with shaking, led to a relatively rapid and strong expression. This phenomenon was confirmed by the in situ hybridization results. In addition to the up-regulation by wounding, NTHK1 expression was also induced following NaCl and PEG treatment, indicating a possible role for NTHK1 in multiple stress responses.