The brassinosteroid receptor BRL3 triggers acclimation to elevated temperature from phloem companion cells in <i>Arabidopsis</i>

Insights into plant receptor signaling are vital in mitigating the impact of climate change and plant disease on agriculture. The role of the BRASSINOSTEROID-INSENSITIVE 1 (BRI1) membrane receptor kinase in promoting growth and development in response to brassinosteroid (BR) hormones is well-established; however, the significance of vascular BRI1-LIKE 1 and 3 (BRL1/3) receptors remains largely overlooked. Here, in Arabidopsis (Arabidopsis thaliana), we reveal that loss of BRL3 causes defects in growth acclimation to elevated temperature. We establish that BRL3 activates the downstream signaling transcription factor BRI1-EMS-SUPPRESSOR 1 (BES1) and regulates the expression of several major growth pathways. We demonstrated via tissue-specific complementation experiments that BRL3 signaling in phloem companion cells is sufficient to regulate thermoresponsive growth. Transcriptome profiling revealed BRL3 regulates growth-related processes, including hormonal homeostasis and the switch to stress responses. Our research uncovers a previously unknown mechanism involving the BRL3 receptor that modulates growth adaptability under elevated temperature conditions, specifically from the phloem companion cells. This discovery challenges the conventional understanding of BR signaling and opens additional possibilities for developing climate-smart crops.