PIF3 is a negative regulator of the<i>CBF</i>pathway and freezing tolerance in<i>Arabidopsis</i>

Abstract

Light and temperature are major environmental factors that coordinately control plant growth and survival. However, how plants integrate light and temperature signals to better adapt to environmental stresses is poorly understood. PHYTOCHROME-INTERACTING FACTOR 3 (PIF3), a key transcription factor repressing photomorphogenesis, has been shown to play a pivotal role in mediating plants' responses to various environmental signals. In this study, we found that PIF3 functions as a negative regulator of <i>Arabidopsis</i> freezing tolerance by directly binding to the promoters of <i>C-REPEAT BINDING FACTOR</i> (<i>CBF</i>) genes to down-regulate their expression. In addition, two F-box proteins, EIN3-BINDING F-BOX 1 (EBF1) and EBF2, directly target PIF3 for 26S proteasome-mediated degradation. Consistently, <i>ebf1</i> and <i>ebf2</i> mutants were more sensitive to freezing than were the wild type, and the <i>pif3</i> mutation suppressed the freezing-sensitive phenotype of <i>ebf1</i> Furthermore, cold treatment promoted the degradation of EBF1 and EBF2, leading to increased stability of the PIF3 protein and reduced expression of the <i>CBF</i> genes. Together, our study uncovers an important role of PIF3 in <i>Arabidopsis</i> freezing tolerance by negatively regulating the expression of genes in the <i>CBF</i> pathway.