Zhu Qiao-Yun, Wang Mei-Jing, Luo Hui-Dan, Zhang Lin-Lin, Lu Hai-Ping, Liu Jian-Xiang
State Key Laboratory of Plant Environmental Resilience, College of Life Sciences, Zhejiang University, Hangzhou, 310027, China.
The National Engineering Laboratory of Crop Stress Resistance Breeding, School of Life Sciences, Anhui Agricultural University, Hefei, 230031, China.
Plant J. 2025 May;122(3):e70204. doi: 10.1111/tpj.70204.
Brassinosteroid (BR) promotes hypocotyl growth at warm temperatures through BZR1 by directly regulating the expression of PIF4, or by interacting with PIF4 to enhance its downstream gene expression; however, how BZR1 level is modulated by warm temperature is not known. We found that the Homology to E6-Associated Carboxy-Terminus (HECT) E3 ubiquitin ligase UPL3 plays an important role in regulating the accumulation of BZR1 under warm temperature conditions. UPL3 interacted with BZR1 both in vitro and in vivo; mutations in UPL3 led to increased BZR1 accumulation levels and accelerated hypocotyl growth under warm temperature conditions, which was inhibited by the BR biosynthesis inhibitor BRZ. The expression of PIF4 and its downstream genes was found to be increased in upl3 mutants, and PIF4 is epistatic to UPL3, further supporting that UPL3 is an upstream regulator of PIF4 in suppressing hypocotyl growth at warm temperatures. Overall, our findings highlight the importance of UPL3 in modulating BZR1 accumulation and, consequently, regulating thermo-responsive hypocotyl growth in Arabidopsis.
油菜素甾醇（BR）在温暖温度下通过BZR1直接调控PIF4的表达，或与PIF4相互作用以增强其下游基因表达，从而促进下胚轴生长；然而，温暖温度如何调节BZR1水平尚不清楚。我们发现，与E6相关羧基末端同源（HECT）的E3泛素连接酶UPL3在温暖温度条件下调控BZR1的积累中起重要作用。UPL3在体外和体内均与BZR1相互作用；UPL3突变导致温暖温度条件下BZR1积累水平增加和下胚轴生长加速，而这被BR生物合成抑制剂BRZ所抑制。研究发现，upl3突变体中PIF4及其下游基因的表达增加，并且PIF4对UPL3上位，进一步支持UPL3是温暖温度下抑制下胚轴生长过程中PIF4的上游调节因子。总体而言，我们的研究结果突出了UPL3在调节BZR1积累以及因此调节拟南芥热响应下胚轴生长中的重要性。
