26S蛋白酶体系统通过有效降解许多关键蛋白因子而调控植物的生长发育和对环境胁迫的响应。26蛋白酶体系统由20S蛋白酶体和19S蛋白酶体两个亚复合物组成。20S蛋白酶体由多个α亚基和β亚基按照α1-7/β1-7/β1-7/α1-7方式组装成一个中空的圆柱体结构。其亚基的突变与人类许多疾病的产生密切相关，包括心血管疾病、糖尿病、神经系统性疾病及癌症等。有趣的是，人体内除标准的蛋白酶体外，20S蛋白酶体还有三种组织特异性形式/类型：免疫型蛋白酶体、胸腺型蛋白酶体和精子型蛋白酶体。另外，氧化胁迫也可以诱导产生胁迫型蛋白酶体。这些特定形式的蛋白酶体介导特定蛋白质在特定细胞环境下降解。然而，目前在植物中还没有关于依赖于细胞特定类型或环境的特异性蛋白酶体的报道。

中国科学院遗传与发育生物学研究所研究员谢旗研究组通过系统地比较盐胁迫和未经胁迫处理的拟南芥幼苗纯化的20S蛋白酶体的亚基，发现盐胁迫增加了20S蛋白酶体中β5亚基PBE蛋白的丰度。同时，发现PBE1基因表达也受到盐胁迫的诱导。PBE1的功能缺失损害了盐胁迫下拟南芥26S蛋白酶体的正常组装，降低了蛋白酶体的活性。这些实验结果揭示了植物中也存在一种特异的胁迫型蛋白酶体。进一步的研究发现，PBE1的缺失导致ABA信号通路关键转录因子ABI5的降解受到抑制，从而影响ABA信号下游一系列响应基因的表达，造成PBE1突变体子叶不变绿的ABA敏感表型。因此，PBE1介导的完整蛋白酶体组装对拟南芥自养生长的成功建立是必需的。综上所述，该研究揭示了PBE1通过调控蛋白酶体的组装和活性，形成胁迫特异性蛋白酶体，参与植物非生物胁迫信号的响应，调控植物幼苗由异养生长向自养生长的转换过程。

上述研究结果于10月10日在线发表在New Phytologist 杂志（DOI：10.1111/nph.15471）。谢旗研究组已出站的博士后韩佳嘉为该论文第一作者。谢旗和浙江大学教授刘建祥是共同通讯作者。该研究得到科技部蛋白质重大专项以及自然科学基金委项目资助。（来源：中国科学院遗传与发育生物学研究所）

The β5 Subunit is Essential for Intact 26S Proteasome Assembly to Specifically Promote Pant Autotrophic Growth under Salt Stress

Abstract  The ubiquitin 26S proteasome (26SP) system efficiently degrades many key regulators of plant development. 26SP consists of two subcomplexes: the catalytic 20S core particle (CP) and the 19S regulatory particle (RP). Previous studies have focused on 19S RP; whether there is a specific subunit in 20S CP that has a stress‐related biological function in plants is unclear. PBE1, one of the β5 subunits of Arabidopsis proteasome CP, is essential for the assembly and proteolytic activity of 26SP in salt‐stressed seedlings. The expression of PBE1 is stress‐induced. During the transition from seed germination to autotrophic growth in salt‐stressed seedlings, loss of PBE1 function results specifically in arrest in developmental transition but not in germination and post‐germination growth. PBE1 is also important for other types of proteasome stress and Endoplasmic Reticulum (ER) stress. PBE1 modulates the protein level of the transcription factor ABI5 and thereby down‐regulates the expression of several genes downstream of this key regulator which are known to be essential for plant growth under stress. Collectively, our results showed PBE1‐mediated intact proteasome assembly that is essential for successful autotrophic growth, and revealed how PBE1 mediated stress proteasome functions to control both proteasome activity and abscisic acid (ABA)‐mediated stress signaling in plants.

原文链接：https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.15471