Biology Department, Coastal Carolina University, 107 Chanticleer Drive, Conway, SC 29526, USA.
Toxicology and Environmental Health. Duke University. 225 B Wing, Levine Science Research Center Durham, North Carolina 27708, USA.
Plant Cell Physiol. 2020 Jun 1;61(6):1028-1040. doi: 10.1093/pcp/pcaa047.
Cellular homeostasis is maintained by the proteasomal degradation of regulatory and misfolded proteins, which sustains the amino acid pool. Although proteasomes alleviate stress by removing damaged proteins, mounting evidence indicates that severe stress caused by salt, metal(oids), and some pathogens can impair the proteasome. However, the consequences of proteasome inhibition in plants are not well understood and even less is known about how its malfunctioning alters metabolic activities. Lethality causes by proteasome inhibition in non-photosynthetic organisms stem from amino acid depletion, and we hypothesized that plants respond to proteasome inhibition by increasing amino acid biosynthesis. To address these questions, the short-term effects of proteasome inhibition were monitored for 3, 8 and 48 h in the roots of Brassica napus treated with the proteasome inhibitor MG132. Proteasome inhibition did not affect the pool of free amino acids after 48 h, which was attributed to elevated de novo amino acid synthesis; these observations coincided with increased levels of sulfite reductase and nitrate reductase activities at earlier time points. However, elevated amino acid synthesis failed to fully restore protein synthesis. In addition, transcriptome analysis points to perturbed abscisic acid signaling and decreased sugar metabolism after 8 h of proteasome inhibition. Proteasome inhibition increased the levels of alternative oxidase but decreased aconitase activity, most sugars and tricarboxylic acid metabolites in root tissue after 48 h. These metabolic responses occurred before we observed an accumulation of reactive oxygen species. We discuss how the metabolic response to proteasome inhibition and abiotic stress partially overlap in plants.
细胞内环境稳态是通过蛋白酶体降解调节蛋白和错误折叠蛋白来维持的，这为氨基酸池提供了支持。虽然蛋白酶体通过清除受损蛋白来缓解压力，但越来越多的证据表明，盐、金属（类金属）和一些病原体造成的严重压力会损害蛋白酶体。然而，蛋白酶体在植物中受到抑制的后果尚未被很好地理解，其功能障碍如何改变代谢活动更是知之甚少。非光合作用生物中蛋白酶体抑制的致死性源自于氨基酸的耗竭，我们假设植物会通过增加氨基酸的生物合成来应对蛋白酶体的抑制。为了解决这些问题，我们在 Brassica napus 的根中监测了蛋白酶体抑制剂 MG132 处理 3、8 和 48 小时后的蛋白酶体抑制的短期影响。蛋白酶体抑制在 48 小时后并未影响游离氨基酸池，这归因于从头合成的氨基酸增加；这些观察结果与早期时间点亚硫酸还原酶和硝酸还原酶活性水平升高一致。然而，升高的氨基酸合成未能完全恢复蛋白质合成。此外，转录组分析表明，蛋白酶体抑制 8 小时后，脱落酸信号转导受到干扰，糖代谢减少。蛋白酶体抑制增加了交替氧化酶的水平，但在 48 小时后降低了柠檬酸合酶的活性，根组织中的大多数糖和三羧酸代谢物也降低了。这些代谢反应发生在我们观察到活性氧积累之前。我们讨论了蛋白酶体抑制和非生物胁迫在植物中部分重叠的代谢反应。
