Distinct thresholds condition sense posttranscriptional gene silencing initiation and amplification

Area of Science:

• Molecular Biology
• Genetics
• Plant Science

Background:

• Pro35S-driven sense transgenes frequently undergo post-transcriptional gene silencing (S-PTGS).
• The precise conditions governing S-PTGS initiation and systemic amplification remain largely unknown.
• Understanding these mechanisms is crucial for transgene stability and gene regulation studies.

Purpose of the Study:

• To elucidate the factors controlling S-PTGS initiation and amplification.
• To investigate the relationship between transgene expression levels and S-PTGS capacity.
• To determine the thresholds required for S-PTGS induction and systemic spread.

Main Methods:

• Genetic screens utilizing chromatin-related mutations.
• Analysis of independent transgenic plant lines with varying transgene expression.
• Experimental setup combining inducible/tissue-specific transgenes with S-PTGS-prone loci.

Main Results:

• Chromatin mutations modulating transgene expression affected S-PTGS amplification but not initiation.
• A direct correlation was observed between transgene expression levels and S-PTGS amplification capacity.
• Transient expression exceeding a threshold was sufficient to initiate systemic S-PTGS.
• Distinct thresholds for aberrant RNA (initiation) and target mRNA (amplification) were proposed.

Conclusions:

• Transgene expression levels are critical for S-PTGS amplification.
• Separate thresholds govern S-PTGS initiation and systemic spread.
• The proposed model applies to endogenous genes, with RNA Quality Control and DCL proteins acting as protective layers.