Temperature-responsive OfARF6 controls flower opening in Osmanthus fragrans through auxin feedback and protein...

Flower opening is crucial for reproductive success in ornamental plants, modulated by diverse cues. In Osmanthus fragrans, this process is particularly influenced by ambient temperature (AT) and auxin signaling pathways. Our previous studies demonstrated that low AT promoted flower opening by increasing endogenous auxin levels. Here, we further showed that flower opening in O. fragrans occurs within a narrow auxin concentration range, as excessive auxin also inhibited this process. We found that OfARF6 was activated in a temperature-dependent manner and its protein stability was finely regulated by auxin levels, undergoing proteasome-mediated degradation when auxin deviated from the optimal range. Transcriptomic analysis revealed that OfARF6 overexpression significantly altered pathways associated with intercellular signaling, metabolism, and cell expansion. Furthermore, OfARF6 interacted with the bHLH protein OfBPEub, enhancing its transcriptional activation of cell expansion-related targets such as OfEXP15-4, thereby linking temperature cues to auxin signaling. Overexpression of OfARF6 in petunia significantly reduced auxin content and impaired flower opening, supporting a model in which excessive OfARF6 activity triggers a negative feedback loop that maintains homeostasis among auxin levels, OfARF6 abundance, and expansin/plasma membrane intrinsic protein (EXP/PIP) transcription during flowering. These findings provide new insights into the molecular mechanisms underlying temperature-dependent flower opening and auxin homeostasis regulation in plants.