PIF4-mediated thermomorphogenesis relies on its oligomerization ability, not DNA-binding or transactivation activity

Area of Science:

• Plant biology
• Molecular biology
• Genetics

Background:

• Plants adjust their growth in response to temperature changes, a process known as thermomorphogenesis.
• PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) is a key transcription factor regulating plant architectural responses to heat.

Purpose of the Study:

• To investigate the specific sequence features of PIF4 that mediate its function in thermomorphogenesis.
• To determine the roles of intrinsically disordered and structured regions of PIF4 in temperature sensing and plant growth.

Main Methods:

• Targeted mutagenesis of PIF4 to alter specific domains.
• In vitro and in planta phase-separation assays to study condensate formation.
• Transgenic complementation in Arabidopsis to assess PIF4 function in plant growth.

Main Results:

• The N-terminal intrinsically disordered region (IDR) of PIF4 is crucial for forming liquid-like condensates.
• A basic segment within the IDR drives PIF4 condensate formation, while the transactivation domain (TAD) modulates condensate properties.
• Disrupting PIF4 oligomerization via mutations in the basic helix-loop-helix (bHLH) domain abolished thermo-induced hypocotyl elongation, while mutations affecting DNA binding or transactivation did not.

Conclusions:

• PIF4's ability to oligomerize is essential for its role in thermomorphogenesis.
• Oligomerization, not DNA binding or transcriptional activity, is the primary driver of PIF4's function in plant response to warm temperatures.