Abstract:

Harpins are bacterial proteins that can enhance plant growth and defense against pathogens and insects. To elaborate whether harpins perform the diverse functions in coordination with the activa-tion of specific promoters that contain particular elements, we cloned pathogen-inducible plant promoters PPP1, PPP2, and PPP3 from tobacco and investigated their responses to harpin_Xoo or its truncated fragments DEG, DIR, and DPR (domains for enhancing plant growth, insect resistance and pathogen resistance). PPP1 contains an internal repeat composed of two tandem 111 bp fragments; 111 bp in the repeat was deleted in PPP2. PPP3 contains a bacteria-inducible element; PPP1 and PPP2 additionally contain TAC-1 and Eli boxes inducible correspondingly by salicylic acid (SA) and elicitors. Function of cloned PPPs was confirmed based on their activation in transgenic Arabidopsis plants by Ralstonia solanacearum (Ralston) or SA. Harpin_Xoo, DEG, DIR, or DPR activated PPP1 and PPP2 but not PPP3, consistent with the presence of Eli boxes in promoters. PPP1 was ca. 3-fold more active than PPP2, suggesting that the internal repeat affects levels of the promoter activation.

Key words: harpin_Xoo, pathogen-inducible plant promoter (PPP), cis-acting elements, transgenic Arabidopsis