Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin 300071, China.
Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin 300071, China
J Exp Bot. 2014 Aug;65(15):4397-408. doi: 10.1093/jxb/eru211. Epub 2014 May 24.
Post-transcriptional control of the expression of the 1-aminocyclopropane-1-carboxylate synthase (ACS) gene family is important for maintaining appropriate levels of ethylene production. However, the molecular mechanism underlying the post-transcriptional regulation of type 3 ACS proteins remains unclear. Multiple sequence alignment revealed that the N-terminus of type 3 ACSs was longer than that of other ACSs. Fusing the N-terminal 54 residues of ACS7, the sole type 3 ACS in Arabidopsis, to the β-glucuronidase (GUS) reporter significantly decreased the stability of N(7(1-54))-GUS fusion protein. Among these 54 residues, residues 1-14 conferred this negative effect on the GUS fusion gene. Consistently, a truncated form of ACS7 lacking residues 1-14 was more stable than full-length ACS7 when transgenically expressed in Arabidopsis and led to a more severe ethylene response phenotype in the light-grown transgenic seedlings. Interestingly, the ACS7 N-terminus had no effect on the stability of N(7)-GUS and ACS7 proteins at the etiolated seedling stage. Both exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) treatment and salt stress could rescue the levels of accumulation of N(7)-GUS fusion protein in light-grown seedlings. These results suggest that the non-catalytic N-terminus of ACS7 is involved in its own post-translational regulation. The proteasome inhibitor MG132 suppressed degradation of full-length ACS7 in vivo, but had little effect on the N-terminal truncated form of ACS7, indicating that the N-terminus mediates the regulation of ACS7 stability through the ubiquitin-26S proteasome pathway.
转录后调控 1-氨基环丙烷-1-羧酸合酶（ACS）基因家族的表达对于维持适当的乙烯产生水平非常重要。然而，3 型 ACS 蛋白的转录后调控的分子机制尚不清楚。多重序列比对显示，3 型 ACSs 的 N 端比其他 ACSs 长。将拟南芥中唯一的 3 型 ACS ACS7 的 N 端 54 个残基与β-葡萄糖醛酸酶（GUS）报告基因融合，显著降低了 N(7(1-54))-GUS 融合蛋白的稳定性。在这 54 个残基中，残基 1-14 对 GUS 融合基因产生了这种负效应。一致地，缺失残基 1-14 的 ACS7 截断形式在拟南芥中转基因表达时比全长 ACS7 更稳定，并导致光生长的转基因幼苗中更严重的乙烯响应表型。有趣的是，ACS7 的 N 端在黄化幼苗阶段对 N(7)-GUS 和 ACS7 蛋白的稳定性没有影响。外源性 1-氨基环丙烷-1-羧酸（ACC）处理和盐胁迫都可以挽救光生长幼苗中 N(7)-GUS 融合蛋白积累水平。这些结果表明，ACS7 的非催化 N 端参与其自身的翻译后调控。蛋白酶体抑制剂 MG132 抑制体内全长 ACS7 的降解，但对 ACS7 的 N 端截断形式几乎没有影响，表明 N 端通过泛素-26S 蛋白酶体途径介导 ACS7 稳定性的调节。
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