Isolation and analysis of a TIR-specific promoter from poplar

A 5' flanking region of the well-conserved Toll/interleukin-1 receptor domain (TIR)-encoding sequence was isolated from the genomic DNA of Melampsora magnusiana Wagner resistant clones of hybrid triploid poplars(Populus tomentosa×P. bolleana)×P. tomentosa. Sequencing results and alignment analysis show that the obtained TIR-specific promoter (named as PtTIRp01) was 1,732 bp in length; moreover 3' region of the PtTIRp01 contains a 398 bp complete TIR-encoding sequence, which significantly corresponds to the 5' composition of TIR-NBS type gene PtDRG02, indicating that the obtained TIR-specific promoter region consists of 747 bp long 5' region of TIR-NBS type gene PtDRG02 and its upstream region of promoter (985 bp). It was found that the 5' region of TIR-NBS type gene PtDRG02 was characterized in the downstream region of the transcriptional start, named as 5'-untranslated region (5' UTR), consisting of one 93 bp 5'-untranslation exon, one 213 bp intron and one 441 bp TIR-encoding open reading frame (ORF). In addition, several putative cis-acting motifs were present in the obtained TIR-specific promoter of PtDRG02, including one TATA box, one GC-rich, one AT-rich, one P-box, one 3-AF1 binding site, two CAAT boxes, two GT-1 motifs, three typical W-boxes, four I-boxes, and one multi-cis-acting fragment (MCF). The latter contains five types of regulatory elements (E4, G-box, ABRE motif, box1 and HVA1s), most of which were homologous to the cis-acting regulatory elements involved in the activation of defense genes in plants. Thus, it can be suggested that TIR-specific promoter might be a pathogen-inducible promoter and be necessary for the inducible expression of defense-related genes.