Cold-induced Arabidopsis FRIGIDA nuclear condensates for FLC repression

Area of Science:

• Plant biology
• Epigenetics
• Molecular mechanisms of flowering time control

Background:

• Plants utilize seasonal temperature cues for reproductive timing.
• Vernalization, involving epigenetic silencing of FLOWERING LOCUS C (FLC) by POLYCOMB REPRESSIVE COMPLEX 2 (PRC2) in Arabidopsis thaliana, aligns flowering with spring.
• Transcriptional downregulation of FLC is essential for silencing, but the mechanism in fluctuating autumn temperatures is unclear.

Purpose of the Study:

• Investigate how fluctuating autumn temperatures regulate FLC transcriptional downregulation.
• Elucidate the role of FRIGIDA (FRI) in FLC repression under cold conditions.
• Understand the plasticity of flowering time control in response to natural temperature variations.

Main Methods:

• Observation of FRI nuclear condensate formation in response to cold.
• Analysis of FRI occupancy at the FLC promoter.
• Assessing the impact of temperature fluctuations on FLC repression.
• Investigating the role of co-transcriptional regulators and COOLAIR RNA in condensate formation.

Main Results:

• Cold rapidly promotes the formation of FRI nuclear condensates, which do not colocalize with active FLC loci.
• Condensate formation correlates with reduced FRI occupancy at the FLC promoter and subsequent FLC repression.
• Warm temperature spikes reverse condensate formation, preventing premature flowering by buffering FLC shutdown.
• Condensate accumulation in cold is influenced by co-transcriptional regulators and a specific COOLAIR RNA isoform.

Conclusions:

• Dynamic partitioning of the transcriptional activator FRI confers plasticity to FLC regulation in response to temperature fluctuations.
• This mechanism enables plants to effectively monitor seasonal progression and optimize flowering time.
• The findings reveal a novel layer of epigenetic regulation for seasonal adaptation in plants.