Fluorescence recovery after photobleaching (FRAP) revealed relatively slow FRI–GFP dynamics (Fig. A FRI–Myc fusion showed similar condensate formation (Extended Data Fig. Like many other co-transcriptional regulators 19, 20 we found that FRI–GFP forms nuclear condensates, which were increased in size and number after cold exposure (Fig. Second, we analysed the localization of FRI in vivo. The higher prevalence of these interactors in extracts from cold-grown plants may reflect the cold-induced accumulation of FRI (Extended Data Table 1). FRI interacted with subunits of the Mediator complex 12, 13, WDR5a and ATX2 (which promote H3K4me3) 7, 9, 14, the PAF1 complex 15, general transcription factors 13, RNA-polymerase-II-associated proteins, and many RNA splicing factors and uridine-rich small nuclear ribonucleoproteins (snRNPs) 16, 17, 18, which suggests that FRI has a role in co-transcriptional regulation (Extended Data Table 1). FRI–GFP did not enrich any of the FRI complex components from warm-grown plant extracts, but, counterintuitively, FRI–GFP accumulated in plants that underwent two weeks of cold exposure, and in these conditions FRL1 and FRL2-but not FLX, SUF4 or FES1-were enriched 8 (Extended Data Table 1). 1), was used for immunoprecipitation in combination with mass spectrometry (IP–MS) 10 (Supplementary Table 1). A line carrying a translational FRI-GFP fusion, expressed at the same level as endogenous FRI, and fully complementing the fri early flowering phenotype (Extended Data Fig.
Our work describes the dynamic partitioning of a transcriptional activator conferring plasticity in response to natural temperature fluctuations, thus enabling plants to effectively monitor seasonal progression.įirst, we analysed how cold influences FRI protein interactions. The accumulation of condensates in the cold is affected by specific co-transcriptional regulators and cold induction of a specific isoform of the antisense RNA COOLAIR 5, 11. Warm temperature spikes reverse this process, buffering FLC shutdown to prevent premature flowering. This correlates with reduced FRI occupancy at the FLC promoter and FLC repression. Here we show that cold rapidly promotes the formation of FRI nuclear condensates that do not colocalize with an active FLC locus. Transcriptional repression correlates with decreased local levels of histone H3 trimethylation at K36 (H3K36me3) and H3 trimethylation at K4 (H3K4me3) 5, 6, which are deposited during FRIGIDA (FRI)-dependent activation of FLC 7, 8, 9, 10. A prerequisite for silencing is transcriptional downregulation of FLC, but how this occurs in the fluctuating temperature regimes of autumn is unknown 2, 3, 4.
This vernalization process aligns flowering with spring. In Arabidopsis thaliana, winter cold epigenetically silences the floral repressor locus FLOWERING LOCUS C ( FLC) through POLYCOMB REPRESSIVE COMPLEX 2 (PRC2) 1. Plants use seasonal temperature cues to time the transition to reproduction.