MAPK phosphorylation-induced stabilization of ACS6 protein is mediated by the non-catalytic C-terminal domain, which also contains the cis-determinant for rapid degradation by the 26S proteasome pathway
MAPK phosphorylation-induced stabilization of ACS6 protein is mediated by the non-catalytic C-terminal domain, which also contains the cis-determinant for rapid degradation by the 26S proteasome pathway
复制标题
DOI：
10.1111/j.1365-313x.2008.03404.x
复制
发表时间：
2008-04-01
期刊：
影响因子：
7.2
通讯作者：
Zhang, Shuqun
中科院分区：
文献类型：
--
作者：
Joo, Sunjoo;Liu, Yidong;Zhang, Shuqun
乙烯是植物生长发育和对环境刺激反应的重要激素。乙烯信号转导途径是通过诱导乙烯生物合成而启动的，乙烯生物合成在转录和转录后水平受到外源和内源信号的严格调控。1-氨基环丙烷-1-羧酸合成酶（ACS）是乙烯生物合成的限速酶。最近，我们发现ACS 2和ACS 6，拟南芥ACS家族的两个异构体，是应激反应的丝裂原活化蛋白激酶（MAPK）级联反应的底物。MPK 6对ACS 2/ACS 6的磷酸化导致ACS蛋白的积累和乙烯的诱导。在这份报告中，我们证明，非磷酸化的ACS 6蛋白被26 S蛋白酶体途径迅速降解。降解机制靶向ACS 6的C-末端非催化结构域，其足以赋予绿色荧光蛋白和荧光素酶报告基因不稳定性。ACS 6的磷酸化将负电荷引入ACS 6的C末端，这降低了降解机制对ACS 6的周转。与此相一致，附近的其他保守的带负电荷的氨基酸残基对于ACS 6稳定性调节是必需的。蛋白质降解和磷酸化是蛋白质翻译后的两种重要修饰。这项研究揭示了这两个重要过程在控制细胞ACS活性水平和乙烯生物合成方面的复杂相互作用。这两个过程的翻译后性质确保了乙烯诱导的快速反应，这是在植物暴露于胁迫后几分钟内可检测到的。
Ethylene is an important hormone in plant growth, development and responses to environmental stimuli. The ethylene-signaling pathway is initiated by the induction of ethylene biosynthesis, which is under tight regulation at both transcriptional and post-transcriptional levels by exogenous and endogenous cues. 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) is the rate-limiting enzyme that catalyzes the committing step of ethylene biosynthesis. Recently, we found that ACS2 and ACS6, two isoforms of the Arabidopsis ACS family, are substrates of a stress-responsive mitogen-activated protein kinase (MAPK) cascade. Phosphorylation of ACS2/ACS6 by MPK6 leads to the accumulation of ACS proteins and the induction of ethylene. In this report, we demonstrate that unphosphorylated ACS6 protein is rapidly degraded by the 26S proteasome pathway. The degradation machinery targets the C-terminal non-catalytic domain of ACS6, which is sufficient to confer instability to green fluorescent protein and luciferase reporters. Phosphorylation of ACS6 introduces negative charges to the C-terminus of ACS6, which reduces the turnover of ACS6 by the degradation machinery. Consistent with this, other nearby conserved negatively charged amino acid residues are essential for ACS6 stability regulation. Protein degradation and phosphorylation are two important post-translational modifications of proteins. This research reveals an intricate interplay between these two important processes in controlling the levels of cellular ACS activity, and thus ethylene biosynthesis. The post-translational nature of both processes ensures a rapid response of ethylene induction, which is detectable within minutes after plants are exposed to stress.