Department of Environmental and Plant Biology, Ohio University, Athens, Ohio, 45701, USA.
Interdisciplinary Program in Molecular and Cellular Biology, Ohio University, Athens, Ohio, 45701, USA.
Plant J. 2022 Sep;111(5):1324-1339. doi: 10.1111/tpj.15891. Epub 2022 Jul 12.
Functional studies of the ubiquitin-26S proteasome system (UPS) have demonstrated that virtually all aspects of the plant's life involve UPS-mediated turnover of abnormal or short-lived proteins. However, the role of the UPS during development, including in seeds and fruits, remains to be determined in detail, although mutants of several of its core elements are known to be embryonically lethal. Unfortunately, early termination of embryogenesis limits the possibility to characterize the activities of the UPS in reproductive organs. Given both the economic and the societal impact of reproductive production, such studies are indispensable. Here, we systematically compared expression of multiple 26S proteasome subunits along with the dynamics of proteasome activity and total protein ubiquitylation in seedlings, developing siliques, and embryos of Arabidopsis thaliana. Since autophagy plays the second largest role in maintaining proteome stability, we parallelly studied three rate-limiting enzymes that are involved in autophagy flux. Our experiments unexpectedly discovered that, in contrast to the activities in seedlings, both protein and transcript levels of six selected 26S proteasome subunits gradually decline in immature siliques or embryos toward maturation while the autophagy flux rises despite the nutrient-rich condition. We also discovered a reciprocal turnover pathway between the proteasome and autophagy. While the autophagy flux is suppressed in seedlings by UPS-mediated degradation of its three key enzymes, transcriptional reprogramming dampens this process in siliques, which in turn stimulates a bulk autophagic degradation of proteasomes. Collectively, our study of the developmental changes of the UPS and autophagy activities suggests that they relay the proteome homeostasis regulation in early silique and/or seed development, highlighting their interactions during development.
泛素-26S 蛋白酶体系统 (UPS) 的功能研究表明，植物生命的几乎所有方面都涉及 UPS 介导的异常或短命蛋白质的周转。然而，UPS 在发育过程中的作用，包括在种子和果实中，仍有待详细确定，尽管其几个核心元件的突变体已知是胚胎致死的。不幸的是，胚胎发生的早期终止限制了在生殖器官中表征 UPS 活性的可能性。鉴于生殖生产的经济和社会影响，这样的研究是不可或缺的。在这里，我们系统地比较了拟南芥幼苗、发育中的蒴果和胚胎中多个 26S 蛋白酶体亚基的表达，以及蛋白酶体活性和总蛋白泛素化的动态。由于自噬在维持蛋白质组稳定性方面发挥着第二大作用，我们平行研究了参与自噬通量的三个限速酶。我们的实验出人意料地发现，与幼苗中的活性相反，在未成熟的蒴果或胚胎中，六个选定的 26S 蛋白酶体亚基的蛋白和转录水平逐渐下降，而自噬通量上升，尽管条件是营养丰富。我们还发现了蛋白酶体和自噬之间的一个相互转化途径。虽然自噬通量在幼苗中被 UPS 介导的三个关键酶的降解所抑制，但在蒴果中，转录重编程抑制了这个过程，这反过来又刺激了蛋白酶体的大量自噬降解。总的来说，我们对 UPS 和自噬活性发育变化的研究表明，它们在早期蒴果和/或种子发育中传递蛋白质组稳态调节，突出了它们在发育过程中的相互作用。
