The promoter of a basic PR1-like gene, AtPRB1, from Arabidopsis establishes an organ-specific expression pattern and responsiveness to ethylene and methyl jasmonate

Antimicrobial proteins are a key feature underlying the deployment of both pre-formed and inducible defence responses. Probably the most well characte rised class are the pathogenesis-related (PR) proteins, which are found in both basic and acidic isoforms. Here we describe the isolation and characte risation of a gene, designated AtPRB1, encoding a basic PR1-like protein fr om Arabidopsis. This protein showed high amino acid sequence identity with basic and acidic PR1 proteins from other plant species, for example PRB1 fr om Nicotiana tabacum and PR1 from Brassica napus, at 64% and 78% identity r espectively. A genomic DNA fragment containing 2345 bp upstream from the pu tative transcriptional start site was fused to the gene encoding the lucife rase (LUC) gene from Photinus pyralis in order to test for promoter activit y. The resulting construct was transformed into Arabidopsis accession Col-0 and analysis of LUC activity, using an ultra-low-light imaging camera syst em, revealed that the AtPRB1 promoter established an exquisite organ-specif ic expression pattern. LUC activity was observed in flowers, stems and root s but not in leaf tissue. Superimposed upon this organ-specific expression pattern was responsiveness, in root tissue, to ethylene and methyl jasmonat e (MeJA), important cues during the establishment of plant disease resistan ce. In contrast, AtPRB1::LUC gene expression was repressed in response to s alicylic acid treatment. Analysis of a limited series of AtPRB1 5'-promoter deletion mutants, identified a number of promoter regions important for bo th the establishment of organ-specific expression and responsiveness to eth ylene and MeJA. While AtPRB1 gene expression was not induced in response to an avirulent isolate of Peronospora parasitica in leaf tissue, this gene m ay contribute to horizontal resistance in other tissues and/or to MeJA- and ethylene-dependent defence responses engaged against necrotrophic pathogen s in root tissue. It is anticipated that transgenic plants containing AtPRB 1-based promoter::reporter constructs will provide useful tools for the fut ure dissection of the cognate signalling networks regulating the expression of this gene.