Stressful environments accelerate the formation of isoaspartyl (isoAsp) residues in proteins, which detrimentally affect protein structure and function. The enzyme PROTEIN l-ISOASPARTYL METHYLTRANSFERASE (PIMT) repairs other proteins by reverting deleterious isoAsp residues to functional aspartyl residues. PIMT function previously has been elucidated in seeds, but its role in plant survival under stress conditions remains undefined. Herein, we used molecular, biochemical, and genetic approaches, including protein overexpression and knockdown experiments, in Arabidopsis to investigate the role of PIMTs in plant growth and survival during heat and oxidative stresses. We demonstrate that these stresses increase isoAsp accumulation in plant proteins, that PIMT activity is essential for restricting isoAsp accumulation, and that both PIMT1 and PIMT2 play an important role in this restriction and Arabidopsis growth and survival. Moreover, we show that PIMT improves stress tolerance by facilitating efficient reactive oxygen species (ROS) scavenging by protecting the functionality of antioxidant enzymes from isoAsp-mediated damage during stress. Specifically, biochemical and MS/MS analyses revealed that antioxidant enzymes acquire deleterious isoAsp residues during stress, which adversely affect their catalytic activities, and that PIMT repairs the isoAsp residues and thereby restores antioxidant enzyme function. Collectively, our results suggest that the PIMT-mediated protein repair system is an integral part of the stress-tolerance mechanism in plants, in which PIMTs protect antioxidant enzymes that maintain proper ROS homeostasis against isoAsp-mediated damage in stressful environments.

中文翻译：

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拟南芥蛋白I-ISOASPARTYL甲基转移酶可修复异天冬氨酰对抗氧化酶的损害，并提高耐热性和氧化应激耐受性。

压力环境会加速蛋白质中异天冬氨酰（isoAsp）残基的形成，这会有害地影响蛋白质的结构和功能。蛋白质1-异戊二烯丙基甲基转移酶（PIMT）通过将有害的isoAsp残基还原为功能性天冬氨酰残基来修复其他蛋白质。以前已经在种子中阐明了PIMT的功能，但是在胁迫条件下其在植物存活中的作用仍然不确定。在本文中，我们在拟南芥中使用了分子，生化和遗传方法，包括蛋白质过表达和敲除实验，以研究PIMT在高温和氧化胁迫下在植物生长和存活中的作用。我们证明这些压力会增加植物蛋白中isoAsp的积累，PIMT活性对于限制isoAsp的积累至关重要，PIMT1和PIMT2都在这种限制以及拟南芥的生长和存活中起着重要的作用。此外，我们表明PIMT通过保护抗氧化剂酶免受isoAsp介导的应激过程中的损害，促进了有效的活性氧（ROS）清除，从而提高了压力耐受性。具体而言，生化和MS / MS分析表明，抗氧化剂酶在胁迫期间会获得有害的isoAsp残基，这会对它们的催化活性产生不利影响，而PIMT可以修复isoAsp残基，从而恢复抗氧化剂的酶功能。总体而言，我们的结果表明，PIMT介导的蛋白质修复系统是植物胁迫耐受机制不可或缺的一部分，