A PR-5 gene promoter from Asparagus officinalis (AoPRT-L) is not induced by abiotic stress, but is activated around sites of pathogen challenge and by salicylate in transgenic tobacco

Summary Using a promoter-uidA (AoPRT-L-GUS) construct, we have characterized heterologous expression controlled by an Asparagus officinalis acidic PR-5 gene promoter. The construct was found to be up-regulated following a variety of treatments with the defence signal salicylate. Similarly, AoPRT-L-GUS was induced by the SA mimic benzothiodiazole, however, unlike salicylate, this compound does not appear to be transported through the vasculature. The construct was insensitive to wounding and to the wound signal jasmonate. Pathogen challenge resulted in a restricted zone of expression at and around the infection site. High levels of NaCl or PEG 8000 failed to induce foliar expression, however, mannitol proved to be an effective inducer when applied as a root drench. The oxidants H2O2 and t-butyl hydroperoxide also failed to induce AoPRT-L-GUS expression. Developmental expression of the construct appeared to be limited to leaf axils, sepal tips, a proportion of anthers and a small segment of tissue just below the stigma. Thus, the AoPRT-L promoter exhibits a limited expression profile responding principally to salicylate-related defence signals, and shows very little developmental expression. This suggests that the AoPRT-L promoter may be an ideal choice for contained gene expression.