A basic-type PR-1 promoter directs ethylene responsiveness, vascular and abscission zone-specific expression

Area of Science:

• Plant Molecular Biology
• Plant Physiology
• Biochemistry

Background:

• Pathogenesis-related (PR) proteins are crucial for plant defense responses.
• The PRB-1b gene in Nicotiana tabacum encodes a basic-type PR-1 protein regulated by ethylene.
• Understanding ethylene-responsive promoter elements is key to deciphering plant defense mechanisms.

Purpose of the Study:

• To identify the minimal ethylene-responsive promoter element for the PRB-1b gene.
• To investigate the expression patterns of PRB-1b under ethylene treatment.
• To correlate promoter function with nuclear protein binding sites.

Main Methods:

• Deletion analysis of the PRB-1b promoter in transgenic tobacco plants.
• Reporter gene assays using beta-glucuronidase (GUS).
• Gel-shift analysis to identify protein-DNA interactions.

Main Results:

• A minimal promoter region of 213 bp was sufficient for a 20-fold increase in GUS expression upon ethylene treatment.
• Sequences of 67 bp were insufficient for ethylene responsiveness.
• Ethylene-inducible constructs showed phloem-specific activity and constitutive expression in abscission zones.
• Gel-shift analysis identified five specific protein-DNA binding sites within the promoter region (-863 to -142 bp).

Conclusions:

• Ethylene induction of PRB-1b requires a promoter region of at least 213 bp.
• The expression pattern suggests a role in pre-emptive plant defense at specific interfaces.
• Constitutive expression in abscission zones may prime defenses against pathogens.