The E3 ligase XBAT35 mediates thermoresponsive hypocotyl growth by targeting ELF3 for degradation in Arabidopsis

Summary Plants are capable of coordination of their growth and development with ambient temperatures. EARLY FLOWERING3 (ELF3), an essential component of the plant circadian clock, is also involved in ambient temperature sensing, as well as in inhibiting the expression and protein activity of the thermoresponsive regulator phytochrome interacting factor 4 (PIF4). The ELF3 activity is subjected to attenuation in response to warm temperature; however, how the protein level of ELF3 is regulated at warm temperature remains less understood. Here, we report that the E3 ligase XB3 ORTHOLOG 5 IN ARABIDOPSIS THALIANA, XBAT35, mediates ELF3 degradation. XBAT35 interacts with ELF3 and ubiquitinates ELF3. Loss‐of‐function mutation of XBAT35 increases the protein level of ELF3 and confers a short‐hypocotyl phenotype under warm temperature conditions. Thus, our findings establish that XBAT35 mediates ELF3 degradation to lift the inhibition of ELF3 on PIF4 for promoting thermoresponsive hypocotyl growth in plants. ELF3, an essential component of circadian clock, is also involved in inhibiting the key thermoregulator PIF4. The Arabidopsis E3 ligase, XBAT35, ubiquitinates and degrades ELF3 under warm temperature conditions to lift the inhibitory effects of ELF3 on PIF4, therefore, promoting thermoresponsive hypocotyl growth in plants.