A novel dual-specificity protein kinase targeted to the chloroplast in tobacco.

The NtDSK1 cDNA encoding a novel chloroplast-targeted protein kinase was identified in Nicotiana tabacum. It contains the kinase domain at the C-terminus and a putative regulatory domain at the N-terminus. The recombinant NtDSK1 underwent autophosphorylation of serine, threonine, and tyrosine residues, indicating that NtDSK1 encodes a functional dual-specificity protein kinase. The NtDSK1-green fluorescent protein fusion protein was targeted to chloroplasts. Furthermore, the NtDSK1 protein was immunodetected in chloroplast fractions isolated from tobacco seedlings. The NtDSK1 mRNA expression was developmentally regulated in different tissues, including anthers and germinating seeds, and strongly stimulated by gibberellin. The mRNA was rapidly light responsive during seedling growth. NtDSK1 may play a role in a light-regulated signaling process in tobacco.