Oligomerization-competent PIF4 drives thermomorphogenesis through functional redundancy in transactivation and DNA binding

Authors: XIONG, HAIBO - University Of Mississippi; BAJRACHARYA, ABHISHESH - University Of Mississippi; ODARI, RANJEETA - University Of Mississippi; BAYER, EDEN - University Of Mississippi; STONER, ALYSSA - University Of Mississippi; WASTI, ANUPA - University Of Mississippi; XI, JING - University Of Mississippi; Baerson, Scott; CHEN, MENG - University Of California, Riverside; QUI, YONGJIAN - University Of Mississippi

Submitted to: Nature Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2026
Publication Date: 3/17/2026
Citation: Xiong, H., Bajracharya, A., Odari, R., Bayer, E.E., Stoner, A., Wasti, A., Xi, J., Baerson, S.R., Chen, M., Qui, Y. 2026. Oligomerization-competent PIF4 drives thermomorphogenesis through functional redundancy in transactivation and DNA binding. Nature Communications. (2026). https://doi.org/10.1038/s41467-026-70748-x.
DOI: https://doi.org/10.1038/s41467-026-70748-x

Interpretive Summary: Warmer temperatures can trigger noticeable changes in plant growth. One of these changes is the elongation of the seedling’s stem, called the hypocotyl, which helps plants adjust the environment. Scientists have known that a protein called PIF4 plays a key role in helping plants respond to warmer temperatures, but how it exactly works remains unknown. In this study, researchers applied a combination of biochemical, molecular, and genetic techniques to understand how PIF4 functions in response to warmer temperature. They discovered that a specific part of the PIF4 protein sequence is critical for its role in promoting hypocotyl elongation. This finding is important because it reveals how plants sense and respond to warmer temperatures. Understanding this process could help scientists develop crops that are better adapted to warmer climate, which is becoming increasingly important as global temperatures continue to rise.

Technical Abstract: Plants tailor their architecture to warm ambient temperatures through the central thermosensory transcription factor PHYTOCHROME-INTERACTING FACTOR 4 (PIF4), yet the sequence features that confer this activity remain poorly defined. Here, we combine targeted mutagenesis, phase-separation assays, and transgenic complementation to dissect PIF4 function in thermomorphogenesis. A long N-terminal intrinsically disordered region (IDR) enables PIF4 to form gel-like condensates in vitro and in planta. Within this IDR, we identify an acidic transactivation domain (TAD) and an extended basic segment that carries a nuclear-localization signal and the canonical basic motif of the basic helix-loop-helix (bHLH) domain. The basic segment--but not the TAD--is both necessary and sufficient to drive PIF4 condensate formation, while the TAD merely tunes condensate properties. Strikingly, alanine substitutions that abolish TAD-mediated transactivation, disrupt DNA binding, or greatly reduce phase-separation propensity have no significant effect on thermomorphogenetic hypocotyl elongation, showing that promoter recognition, transcriptional activation, and condensate formation are all dispensable for PIF4 function. By contrast, replacing three conserved basic residues in the first helix of the HLH domain disrupts PIF4 oligomerization and abolishes thermo-induced hypocotyl growth. We conclude that the ability of PIF4 to oligomerize, rather than to bind DNA or recruit the transcriptional machinery, is the primary determinant of its thermomorphogenetic activity.