PIF4 controls autophagy during hypocotyl response to elevated ambient temperatures via ArpC5 in Arabidopsis

Abstract

Increased hypocotyl elongation is a key adaptive response of plants to high ambient temperatures (HATs). However, the underlying molecular mechanisms remain to be elucidated. This study identifies the role of ArpC5, a subunit of the ACTIN-RELATED PROTEIN 2/3(Arp2/3) complex, in Arabidopsis hypocotyl response to HAT. We demonstrate that PIF4 induces ArpC5 expression upon HAT exposure to regulate autophagy. ArpC5 promotes the assembly of actin cables essential for autophagosome formation. Additionally, ArpC5 interacts with ATG8 to facilitate autophagosome association and movement along actin cables under HAT conditions. Activated autophagy is required for the degradation of the auxin transporter and regulates polar auxin transport to drive hypocotyl cell elongation in response to HAT. Collectively, these findings elucidate the PHYTOCHROME-INTERACTING FACTOR 4 (PIF4)-Arp2/3 complex-actin cytoskeleton-autophagy axis and underscore its role in plant growth adaptation to elevated temperatures.