A family of dispersed repetitive DNA sequences in tobacco contain clusters of W-box elements recognized by pathogen-induced WRKY DNA-binding proteins

Abstract

We have previously identified in tobacco ( Nicotiana tabacum) a group of pathogen- and salicylic acid (SA)-induced DNA-binding proteins that contain the highly conserved WRKY DNA-binding domain. In order to identify their potential target genes, we have isolated tobacco genomic DNA sequences that contain the consensus TTGAC(C/T) binding sites (W boxes) recognized by WRKY DNA-binding proteins. Surprisingly, sequence analysis of the 16 clones with the strongest binding affinities for the WRKY proteins indicated that they all belong to a family of dispersed repetitive DNA sequences with an approximate copy number of 10,000 per haploid tobacco genome. These repetitive DNA sequences contain a number of direct and inverted repeats, a feature commonly attributed to mobile genetic elements. BLAST search revealed that similar repetitive sequences are present in the promoters of the tobacco par/ str246C gene and the gene encoding a feedback-insensitive anthranilate synthase α-2 chain. Interestingly, the par/ str246C gene, which contains a W-box element in the repetitive sequence of its promoter, was induced dramatically in resistant tobacco plants after infection with tobacco mosaic virus. These results support that dispersed repetitive DNA sequences may serve as reservoirs for new functional cis-acting DNA elements that can be recruited through chromosomal rearrangement to participate in transcriptional regulation of nearby genes.