Isolation of an RNA-directed RNA polymerase-specific cDNA clone from tomato

Area of Science:

• Plant molecular biology
• Enzymology
• Genetics

Background:

• RNA-directed RNA polymerase (RdRP) is crucial in RNA silencing pathways.
• The specific function and characterization of plant RdRPs remain largely elusive.
• Understanding RdRP is key to deciphering gene regulation and defense mechanisms in plants.

Purpose of the Study:

• To isolate and characterize a novel RNA-directed RNA polymerase (RdRP) from tomato.
• To investigate the expression and enzymatic activity of the identified tomato RdRP.
• To explore the evolutionary conservation and potential role of RdRP in gene silencing.

Main Methods:

• Isolation and sequencing of a 3600-bp cDNA encoding a putative RdRP.
• Antibody production against synthetic peptides for protein detection.
• Enzymatic activity assays and protein purification using various chromatography techniques.
• DNA gel blot analysis and polymerase chain reaction (PCR) for gene analysis.
• Sequence homology searches across different species.

Main Results:

• A 3600-bp RdRP-specific cDNA with an 1114-amino acid open reading frame was isolated from tomato.
• The encoded protein, a 127-kD tomato RdRP, showed no homology to known proteins but was specifically detected by custom antibodies.
• Enzymatic activity correlated with protein purification, and a single copy of the RdRP gene was found in tomato.
• RdRP homologs were identified in other plants (petunia, Arabidopsis, tobacco, wheat), yeast, and a nematode, indicating evolutionary conservation.
• RdRP activity induction upon viroid infection was linked to increased mRNA levels.

Conclusions:

• A novel tomato RdRP has been identified and characterized.
• The study provides evidence for the conserved nature of RdRP across eukaryotes.
• The findings suggest a potential role for this plant RNA polymerase in homology-dependent gene silencing.