Autophagy is a highly conserved and regulated catabolic process involved in the degradation of protein aggregates, which plays critical roles in eukaryotes. In plants, multiple molecular processes can induce or suppress autophagy but the mechanism of its regulation by phytohormones is poorly understood. Brassinosteroids (BRs) are steroid phytohormones that play crucial roles in plant response to stresses. Here, we investigate the role of BRs in NBR1-dependent selective autophagy in response to chilling stress in tomato. BRs and their signaling element BZR1 can induce autophagy and accumulation of the selective autophagy receptor NBR1 in tomato under chilling stress. Cold increased the stability of BZR1, which was promoted by BRs. Cold- and BR-induced increased BZR1 stability activated the transcription of several autophagy-related genes (ATGs) and NBR1 genes by directly binding to their promoters, which resulted in selective autophagy. Furthermore, silencing of these ATGs or NBR1 genes resulted in a decreased accumulation of several functional proteins and an increased accumulation of ubiquitinated proteins, subsequently compromising BR-induced cold tolerance. These results strongly suggest that BRs regulate NBR1-dependent selective autophagy in a BZR1-dependent manner in response to chilling stress in tomato.

中文翻译：

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油菜素类固醇作为NBR1依赖性选择性自噬的正调节剂，响应番茄的低温胁迫。

自噬是涉及蛋白质聚集体降解的高度保守和调控的分解代谢过程，其在真核生物中起关键作用。在植物中，多种分子过程可以诱导或抑制自噬，但是对植物激素调节其自噬的机制了解甚少。油菜素类固醇（BRs）是类固醇植物激素，在植物对逆境的反应中起着至关重要的作用。在这里，我们研究了BRs在依赖于NBR1的选择性自噬中响应番茄冷胁迫的作用。BRs及其信号转导元件BZR1可以诱导低温胁迫下番茄中的自噬和选择性自噬受体NBR1的积累。寒冷增强了BR促进的BZR1的稳定性。寒冷和BR诱导的BZR1稳定性增加，通过直接结合它们的启动子来激活几个自噬相关基因（ATG）和NBR1基因的转录，从而导致选择性自噬。此外，这些ATG或NBR1基因的沉默导致几种功能蛋白的积累减少，泛素化蛋白的积累增加，从而损害了BR诱导的耐寒性。这些结果强烈表明，BRs以BZR1依赖性方式调节NBR1依赖性选择性自噬，以响应番茄的低温胁迫。随后损害了BR引起的耐寒性。这些结果强烈表明，BRs以BZR1依赖性方式调节NBR1依赖性选择性自噬，以响应番茄的低温胁迫。随后损害了BR引起的耐寒性。这些结果强烈表明，BRs以BZR1依赖性方式调节NBR1依赖性选择性自噬，以响应番茄的低温胁迫。