The ELF3-BBX24/25-PIF4 module regulates thermosensory growth in Arabidopsis

In Arabidopsis, B-BOX domain-containing proteins, BBX24 and BBX25, play a key role in inhibiting photomorphogenesis. However, their role in temperature-mediated regulation of
growth remains unknown. Here, we show that BBX24/BBX25 are essential for warm temperature-mediated growth. Analysis of bbx24 bbx25 double mutants show strong insensitivity
to warm temperature-mediated hypocotyl growth, which is due to the reduced expression of growth-related genes. However, the overexpression lines show enhanced hypocotyl
growth. Warm temperature enhances the gene expression and protein stability of BBX24/25. Epistatic analysis suggests that BBX24 and BBX25 function in the same pathway as
PHYTOCHROME INTERACTING FACTOR 4 and are essential for PIF4-mediated thermomorphogenic growth. BBX24 and BBX25 promote PIF4 protein stability, probably through
physical interaction. Furthermore, EARLY FLOWERING 3, a key negative regulator of thermosensory growth, functions upstream and inhibits BBX24 and BBX25 gene expression,
depicting an indirect pathway of regulation of PIF4 activity by ELF3. Thus, our study uncovered a novel mechanism through which plants integrate temperature cues and promote
warm temperature-mediated growth.