Sara Kim1, Geonhee Hwang1, Soohwan Kim1, Thom Nguyen Thi2, Hanim Kim3, Jinkil Jeong4, Jaewook Kim5, Jungmook Kim2, Giltsu Choi3 & Eunkyoo Oh1,*
1 Department of Life Sciences, Korea University, Seoul, Korea.
2 Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 61186, Korea.
3 Department of Biological Sciences, KAIST, Daejeon, Korea.
4 Molecular and Cell Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
5 Faculty of Agriculture, Kyushu University, Fukuoka 819-0395, Japan
*Correspondence to Eunkyoo Oh
In plants, an elevation in ambient temperature induces adaptive morphological changes including elongated hypocotyls, which is predominantly regulated by a bHLH transcription factor, PIF4. Although PIF4 is expressed in all aerial tissues including the epidermis, mesophyll, and vascular bundle, its tissue-specific functions in thermomorphogenesis are not known. Here, we show that epidermis-specific expression of PIF4 induces constitutive long hypocotyls, while vasculature-specific expression of PIF4 has no effect on hypocotyl growth. RNA-Seq and qRT-PCR analyses reveal that auxin-responsive genes and growth-related genes are highly activated by epidermal, but not by vascular, PIF4. Additionally, inactivation of epidermal PIF4 or auxin signaling, and overexpression of epidermal phyB suppresses thermoresponsive growth, indicating that epidermal PIF4-auxin pathways are essential for the temperature responses. Further, we show that high temperatures increase both epidermal PIF4 transcription and the epidermal PIF4 DNA-binding ability. Taken together, our study demonstrates that the epidermis regulates thermoresponsive growth through the phyB-PIF4-auxin pathway.