A two-component gene (NTHK1) encoding a putative ethylene-receptor homologis 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 previo usly obtained NTHK1 cDNA fragment as a probe. Sequence analysis revealed th at NTHK1 shared high homology with LeETR4 from tomato and encoded an ethyle ne-receptor homolog. The predicted NTHK1 protein had a putative signal pept ide, three transmembrane domains, a histidine kinase domain and a receiver domain. The putative autophosphorylation site at His378 and the phosphate r eceiver site at Asp689 were also identified. By using the in situ hybridiza tion technique, NTHK1 mRNA was detected during flower organ development. It is also highly expressed in the processes of pollen formation and embryo d evelopment. The expression of NTHK1 in response to wounding and other stres ses was investigated using competitive RT-PCR. The results demonstrated tha t NTHK1 was inducible upon wounding (cutting). Floating of the cut leaf pie ces in 0.5 x MS, with shaking, led to a relatively rapid and strong express ion. This phenomenon was confirmed by the in situ hybridization results. In addition to the up-regulation by wounding, NTHK1 expression was also induc ed following NaCl and PEG treatment, indicating a possible role for NTHK1 i n multiple stress responses.