The Cytokinin Oxidase/Dehydrogenase CKX1 Is a Membrane-Bound Protein Requiring Homooligomerization in the Endoplasmic Reticulum for Its Cellular Activity1
The Cytokinin Oxidase/Dehydrogenase CKX1 Is a Membrane-Bound Protein Requiring Homooligomerization in the Endoplasmic Reticulum for Its Cellular Activity1
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DOI：
10.1104/pp.17.00925
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发表时间：
2018-01
期刊：
影响因子：
7.4
通讯作者：
Michaela Niemann;H. Weber;Tomáš Hluska;Georgeta Leonte;S. Anderson;O. Novák;A. Senes;T. Werner
中科院分区：
文献类型：
--
作者：
Michaela Niemann;H. Weber;Tomáš Hluska;Georgeta Leonte;S. Anderson;O. Novák;A. Senes;T. Werner
拟南芥细胞分裂素氧化酶/脱氢酶CKX1在内质网细胞分裂素降解中起关键作用。植物激素细胞分裂素的降解是由细胞分裂素氧化酶/脱氢酶（CKX）控制的。这些蛋白质的分子和细胞行为在很大程度上仍然是未知的。在这项研究中，我们发现CKX1是一种II型单遍膜蛋白，主要定位于拟南芥（Arabidopsis thaliana）的内质网（ER）。这表明这个CKX亚型是一个真正的内质网蛋白，直接控制细胞分裂素，触发内质网的信号。通过使用各种方法，我们证明CKX1在体内形成同型二聚体和同型寡聚体。CKX1的氨基末端部分对于蛋白质的寡聚以及在内质网中的靶向和保留是必要和充分的。此外，我们发现蛋白质-蛋白质相互作用在很大程度上是由跨膜螺旋促进的，并依赖于一个功能性的gxxx -样相互作用基序。重要的是，CKX1单体的突变会干扰其在内质网中的稳态定位，并通过增加其内质网相关降解导致CKX1生物活性的丧失。因此，我们的研究提供了证据，证明寡聚化是调节CKX1生物活性和内质网细胞分裂素浓度的关键参数。这项工作也为内质网的细胞分裂素信号传导和细胞分裂素池在这个隔室中的功能相关性提供了强有力的支持。
The Arabidopsis cytokinin oxidase/dehydrogenase CKX1 plays a key role in cytokinin degradation in the endoplasmic reticulum. Degradation of the plant hormone cytokinin is controlled by cytokinin oxidase/dehydrogenase (CKX) enzymes. The molecular and cellular behavior of these proteins is still largely unknown. In this study, we show that CKX1 is a type II single-pass membrane protein that localizes predominantly to the endoplasmic reticulum (ER) in Arabidopsis (Arabidopsis thaliana). This indicates that this CKX isoform is a bona fide ER protein directly controlling the cytokinin, which triggers the signaling from the ER. By using various approaches, we demonstrate that CKX1 forms homodimers and homooligomers in vivo. The amino-terminal part of CKX1 was necessary and sufficient for the protein oligomerization as well as for targeting and retention in the ER. Moreover, we show that protein-protein interaction is largely facilitated by transmembrane helices and depends on a functional GxxxG-like interaction motif. Importantly, mutations rendering CKX1 monomeric interfere with its steady-state localization in the ER and cause a loss of the CKX1 biological activity by increasing its ER-associated degradation. Therefore, our study provides evidence that oligomerization is a crucial parameter regulating CKX1 biological activity and the cytokinin concentration in the ER. The work also lends strong support for the cytokinin signaling from the ER and for the functional relevance of the cytokinin pool in this compartment.