Proteasome-associated HECT-type ubiquitin ligase activity is required for plant immunity.
Proteasome-associated HECT-type ubiquitin ligase activity is required for plant immunity.
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DOI：
10.1371/journal.ppat.1007447
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发表时间：
2018-11
期刊：
影响因子：
6.7
通讯作者：
Spoel SH
中科院分区：
文献类型：
--
作者：
Furniss JJ;Grey H;Wang Z;Nomoto M;Jackson L;Tada Y;Spoel SH
26S蛋白酶体调节蛋白质降解在真核细胞的维持和信号传导中起重要作用。蛋白质通过E3连接酶的作用被标记为降解，E3连接酶通过添加泛素链特异性修饰其底物。植物的先天免疫信号深深地依赖于泛素- 26s蛋白酶体系统。虽然在了解植物免疫过程中的底物泛素化方面取得了进展，但这些底物在到达蛋白酶体时是如何加工的仍不清楚。本研究表明，含HECT结构域的泛素蛋白连接酶（UPL）家族的特定成员在植物免疫过程中蛋白酶体底物加工中发挥重要作用。UPL1、UPL3和UPL5的突变显著降低了免疫激素水杨酸（SA）激活的免疫应答。对upl3突变体的深入分析表明，这些植物在几乎整个sa诱导的转录组重编程中受损，并且无法对半生物营养病原体建立免疫力。up3被发现与蛋白酶体的调节颗粒和其他泛素- 26s蛋白酶体途径组分发生物理相互作用。与此一致，我们证明了up3使蛋白酶体形成多泛素链，从而调节细胞的总多泛素化水平。综上所述，我们的研究结果表明，up3的蛋白酶体相关泛素连接酶活性促进了蛋白酶体的加工，对植物免疫的发展是不可或缺的。植物不断暴露于不同的致病因子，包括细菌、真菌、卵菌和咀嚼或吸吮昆虫。为了保护自己，植物已经进化出一个复杂的多层免疫系统，它依赖于大基因库的重编程，优先考虑免疫基因的表达，而不是正常的细胞家庭基因。蛋白酶体是一种降解蛋白质的大型蛋白水解复合物，其活性对协调免疫基因的表达至关重要。虽然众所周知，由小多肽泛素链标记的蛋白质可以靶向蛋白酶体进行降解，但仍不清楚蛋白酶体如何处理这些蛋白质。在这里，我们发现了up3酶，它使植物蛋白酶体自身能够向细胞蛋白中添加更多的泛素链，以进行降解。这被认为是一个重要的活性，增加底物对蛋白酶体的亲和力，同时防止它们在降解过程中停滞。重要的是，我们证明了UPL3的这种活性对于基因表达重编程和抗病能力的建立是必不可少的。因此，通过使蛋白酶体在其底物上添加泛素标记，UPL3可以调节植物免疫的关键方面，这可以在未来的作物保护策略中进一步利用。
Regulated degradation of proteins by the 26S proteasome plays important roles in maintenance and signalling in eukaryotic cells. Proteins are marked for degradation by the action of E3 ligases that site-specifically modify their substrates by adding chains of ubiquitin. Innate immune signalling in plants is deeply reliant on the ubiquitin-26S proteasome system. While progress has been made in understanding substrate ubiquitination during plant immunity, how these substrates are processed upon arrival at the proteasome remains unclear. Here we show that specific members of the HECT domain-containing family of ubiquitin protein ligases (UPL) play important roles in proteasomal substrate processing during plant immunity. Mutations in UPL1, UPL3 and UPL5 significantly diminished immune responses activated by the immune hormone salicylic acid (SA). In depth analyses of upl3 mutants indicated that these plants were impaired in reprogramming of nearly the entire SA-induced transcriptome and failed to establish immunity against a hemi-biotrophic pathogen. UPL3 was found to physically interact with the regulatory particle of the proteasome and with other ubiquitin-26S proteasome pathway components. In agreement, we demonstrate that UPL3 enabled proteasomes to form polyubiquitin chains, thereby regulating total cellular polyubiquitination levels. Taken together, our findings suggest that proteasome-associated ubiquitin ligase activity of UPL3 promotes proteasomal processivity and is indispensable for development of plant immunity. Plants are continuously exposed to different disease agents, including bacteria, fungi, oomycetes and chewing or sucking insects. To protect themselves plants have evolved a sophisticated multi-layered immune system that depends on the reprogramming of large gene repertoires to prioritize the expression of immune genes over normal cellular household genes. Activity of the proteasome, a large proteolytic complex that degrades proteins, is vital to coordinate the expression of immune genes. While it is well understood that proteins marked by a chain of the small polypeptide ubiquitin can be targeted to the proteasome for degradation, it remains unclear how these proteins are processed by proteasomes. Here we identify the enzyme UPL3 that enabled plant proteasomes themselves to add further ubiquitin chains to cellular proteins destined for degradation. This is thought to be an important activity that increases the affinity of substrates for proteasomes while preventing them from stalling during degradation. Importantly, we show that this activity of UPL3 is indispensable for gene expression reprogramming and establishment of disease resistance. Thus, by enabling proteasomes to add ubiquitin marks to its substrates, UPL3 regulates key aspects of plant immunity that could be further exploited in future crop protection strategies.
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