CUL3 LRB E3 ubiquitin ligases control thermosensory growth in Arabidopsis by differentially regulating HY5 and PIF4 protein stability

Rising temperatures from global warming harm plant health, reducing crop yields and threatening food security. Understanding the impact of climate change on plant health is crucial for developing climate-resilient crops. Here, we report LIGHT-RESPONSE BRIC-A-BRACK/TRAMTRACK/BROAD (LRB) E3 ubiquitin ligases as essential components of thermosensory growth in Arabidopsis. Single lrb mutants show subtle to moderate warm temperature insensitivity, while lrb12 double and lrb123 triple mutants exhibit complete insensitivity. Whole-genome transcriptomic analysis revealed that LRBs are crucial for the warm temperature-induced expression of genes involved in growth and hormone signaling. Genetic and gene expression analyses confirm that the LRBs are essential for PHYTOCHROME INTERACTING FACTOR 4 (PIF4)-mediated thermomorphogenesis. LRBs physically associate with PIF4, likely preventing its degradation and maintaining optimal protein levels. Concurrently, LRBs ubiquitinate and degrade the key repressor ELONGATED HYPOCOTYL5 during the daytime, thereby enhancing PIF4 signaling. Together, this study uncovers a dual mechanism by which LRBs potentiate thermosensory growth in response to warm ambient temperatures.