Repression by the Arabidopsis TOPLESS corepressor requires association with the core mediator complex

Area of Science:

• Plant molecular biology
• Gene regulation
• Yeast genetics

Background:

• The plant corepressor TOPLESS (TPL) regulates gene expression but its repression mechanisms are unclear.
• Previous studies utilized an Arabidopsis thaliana TPL N-terminus in yeast to repress an auxin response circuit.

Purpose of the Study:

• To investigate the structure-function relationship of TOPLESS (TPL) by identifying its repression domains.
• To elucidate the molecular mechanisms underlying TPL-mediated transcriptional repression.

Main Methods:

• Utilized a Saccharomyces cerevisiae (yeast) system to screen for TPL repression domains.
• Investigated interactions between TPL and Mediator complex subunits using yeast and plant systems.
• Assessed the role of TPL multimer formation in repression strength.

Main Results:

• Identified a potent repression domain in Helix 8 within the TPL CRA domain.
• Demonstrated direct interaction between TPL's Helix 8 domain and Mediator subunits Med21 and Med10.
• Confirmed that TPL-Mediator interactions are essential for transcriptional repression in both yeast and plants.
• Found that TPL multimerization has a negligible effect on repression efficacy.

Conclusions:

• The Helix 8 domain of TPL, interacting with the Mediator complex, is a key functional repression module.
• TPL-Mediator interaction is a conserved mechanism for transcriptional repression across species.
• TPL's repression function is primarily mediated by direct interaction with Mediator, not multimerization.