biostudies-literatureUnknown17(1)Zhang DWhen Arabidopsis plants are exposed to warm temperatures (e.g., 29 °C), they undergo adaptive growth known as thermomorphogenesis. This process is primarily regulated by the phytochrome B (phyB)-PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) module; however, the potential involvement of additional signaling pathways remains underexplored. Here, we show that warmth triggers endoplasmic reticulum (ER) stress, activating both arms of the Unfolded Protein Response (UPR). Three UPR-associated bZIP transcription factors, bZIP17, bZIP28 and bZIP60, promote hypocotyl growth under warmth in a PIF4-dependent manner. Active bZIP factors form complexes with PIF4 in the nucleus, where they bind to promoter regions of PIF4 and other growth-related genes to enhance their expression. In parallel, bZIPs overexpression counteract the inhibitory effect of phyB on PIF4 stability, thereby reinforcing thermomorphogenic growth. Together, our findings define a regulatory axis that links ER stress, the UPR and thermomorphogenesis, clarifying how plants coordinate physiological and environmental cues to adapt to warming conditions.Nature communications1151https://www.ebi.ac.uk/biostudies/studies/S-EPMC12858828biostudies-literaturebZIP factors of the Unfolded Protein Response interact with PIF4 to promote thermomorphogenesis.PMC12858828Zhang DXu HChua NHfalsebZIP factors of the Unfolded Protein Response interact with PIF4 to promote thermomorphogenesis.When Arabidopsis plants are exposed to warm temperatures (e.g., 29 °C), they undergo adaptive growth known as thermomorphogenesis. This process is primarily regulated by the phytochrome B (phyB)-PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) module; however, the potential involvement of additional signaling pathways remains underexplored. Here, we show that warmth triggers endoplasmic reticulum (ER) stress, activating both arms of the Unfolded Protein Response (UPR). Three UPR-associated bZIP transcription factors, bZIP17, bZIP28 and bZIP60, promote hypocotyl growth under warmth in a PIF4-dependent manner. Active bZIP factors form complexes with PIF4 in the nucleus, where they bind to promoter regions of PIF4 and other growth-related genes to enhance their expression. In parallel, bZIPs overexpression counteract the inhibitory effect of phyB on PIF4 stability, thereby reinforcing thermomorphogenic growth. Together, our findings define a regulatory axis that links ER stress, the UPR and thermomorphogenesis, clarifying how plants coordinate physiological and environmental cues to adapt to warming conditions.2025-01-01T00:00:00Z2025 Dec2026-06-11T06:01:55.895Z2026-06-11T03:12:19.308ZS-EPMC128588284146938210.1038/s41467-025-67909-9