# CUL3LRB E3 ubiquitin ligases control thermosensory growth in Arabidopsis by differentially regulating HY5 and PIF4 protein stability

## TL;DR

This study shows how LRB proteins help plants sense and respond to warm temperatures by controlling key growth regulators.

## Contribution

The paper reveals a dual mechanism by which LRBs regulate PIF4 and HY5 to control thermosensory growth in plants.

## Key findings

- LRB mutants show reduced or no response to warm temperatures.
- LRBs stabilize PIF4 and degrade HY5 to promote thermomorphogenesis.
- Transcriptomic analysis links LRBs to warm temperature–induced gene expression.

## Abstract

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.

LRBs potentiate thermosensory growth by inhibiting HY5 activity while promoting PIF4 function.