Elicitor-induced activation of transcription via W box-related cis-acting elements from a basic chitinase gene by WRKY transcription factors in tobacco.

A putative elicitor responsive element with two W boxes (CTGACC/T) has been identified in the region between -125 and -69 of a tobacco class I basic chitinase gene CHN48. We generated transgenic tobacco calli that contained the -125/-69 region fused to a luciferase reporter gene. The expression of the reporter gene was induced upon treatment with an elicitor, xylanase from Trichoderma viride (TvX). This induction required protein kinase activity. We isolated three cDNA clones encoding DNA-binding proteins, designated as NtWRKY1, NtWRKY2, and NtWRKY4, from tobacco cultured cells. Gel mobility shift assays showed that in vitro translation products of NtWRKY1, NtWRKY2 and NtWRKY4 bound to W box of CHN48 gene. These NtWRKY proteins stimulated W box-mediated transcription of a luciferase reporter gene in the transient assay. In addition, the transactivation of W box-mediated transcription by NtWRKY1 and NtWRKY4 was enhanced in response to elicitor treatment, suggesting elicitor-induced posttranscriptional activation of these NtWRKYs. Northern blot analyses showed that mRNAs for NtWRKY1 and NtWRKY2 increased after treatment with the elicitor, whereas mRNAs for NtWRKY4 were expressed constitutively at a low level. These results suggested possible involvement of NtWRKYs in elicitor-responsive transcription of defense genes in tobacco.