A nuclear casein kinase 2 activity is involved in early events of transcriptional activation induced by salicylic acid in tobacco

Salicylic acid (SA) activates immediate early transcription of genes contro lled by a family of DNA promoter elements named ns-l-like elements. These e lements are functional in the promoter of glutathione S-transferase genes. We have previously shown that SA increases the binding of tobacco (Nicotian a tabacum cv Xanthi nc) nuclear factors to the ns-1 sequence in a process m ediated by protein phosphorylation. In this study we give evidence for the participation of a nuclear protein kinase CK2 (casein kinase 2) in the path way activated by SA in tobacco. The first line of evidence comes from the e valuation of the CK2 activity in nuclear extracts prepared from tobacco pla nts treated with SA or water as a control. Results from these experiments i ndicate that SA increases the nuclear CK2 activity. The second line of evid ence derives from the evaluation of the in vivo effect of 5,6-dichloro-l-(b eta-(D)-ribofuranosyl) benzimidazole (DRB), a cell-permeable CK2 inhibitor, on the responsiveness of the as-1 sequence to SA. Results from these exper iments indicate that DRB impairs the activating effect of SA on the transcr iption of both, the GLIS reporter gene controlled by a tetramer of the as-1 element, and the endogenous gnt35 gene encoding a glutathione S-transferas e, in transgenic tobacco plants. DRB also impaired the increasing effect of SA on the binding of nuclear factors to the as-1 element. Furthermore, tra nscription of the as-1/GUS reporter gene activated by the synthetic auxin 2 ,4-dichlorophenoxyacetic acid and by methyl jasmonate was also inhibited by DRB. To our knowledge, this is the first report in which activation of a C K2 enzyme by a plant hormone is reported.