Thermosensory pathway makes a U-turn to respond to heat

Heat stress in Arabidopsis thaliana seedlings triggers phytochrome B (phyB) to form enlarged nuclear condensates and actively suppress cotyledon auxin/PIF4-driven growth.

• Why it matters: The mechanistic switch between growth-promoting and growth-inhibiting temperature ranges is unresolved, limiting understanding of how plants reverse thermomorphogenesis programs.
• What they did: In seedlings, the study tracked auxin levels, auxin signalling, and PIF4 abundance in cotyledons across temperatures, while imaging phyB nuclear bodies; it also reproduced the enlarged condensates in mammalian cells.
• The result: Temperatures beyond the growth optimum downregulate auxin, auxin signalling, and PIF4 specifically in cotyledons, implying heat inhibition is an active reversal of the warm-promotive pathway rather than passive damage.

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