Department of Plant and Environmental Sciences, University of Copenhagen , Frederiksberg 1871, Denmark.
Copenhagen Plant Science Center, University of Copenhagen , Frederiksberg 1871, Denmark.
Philos Trans R Soc Lond B Biol Sci. 2024 Nov 18;379(1914):20230365. doi: 10.1098/rstb.2023.0365. Epub 2024 Sep 30.
Plant glutathione transferases (GSTs) constitute a large and diverse family of enzymes that are involved in plant stress response, metabolism and defence, yet their physiological functions remain largely elusive. Consistent with the traditional view on GSTs across organisms as detoxification enzymes, most plant GSTs catalyse glutathionylation, conjugation of the tripeptide glutathione (GSH; γ-Glu-Cys-Gly) onto reactive molecules. However, when it comes to elucidating GST functions, it remains a key challenge that the endogenous plant glutathione conjugates (GS-conjugates) that would result from such glutathionylation reactions are rarely reported. Furthermore, GSTs often display high substrate promiscuity, and their proposed substrates are prone to spontaneous chemical reactions with GSH; hence, single-gene knockouts rarely provide clear chemotypes or phenotypes. In a few cases, GS-conjugates are demonstrated to be biosynthetic intermediates that are rapidly further metabolized towards a pathway end product, explaining their low abundance and rare detection. In this review, we summarize the current knowledge of plant GST functions and how and possibly why evolution has resulted in a broad and extensive expansion of the plant GST family. Finally, we demonstrate that endogenous GS-conjugates are more prevalent in plants than assumed and suggest they are overlooked as clues towards the identification of plant GST functions. This article is part of the theme issue 'The evolution of plant metabolism'.
植物谷胱甘肽转移酶（GSTs）是一个庞大而多样化的酶家族，参与植物应激反应、代谢和防御，但它们的生理功能仍很大程度上难以捉摸。与 GSTs 在所有生物体中作为解毒酶的传统观点一致，大多数植物 GSTs 催化谷胱甘肽化，即三肽谷胱甘肽（GSH；γ-Glu-Cys-Gly）与反应性分子的缀合。然而，在阐明 GST 功能时，一个关键的挑战仍然是，源于此类谷胱甘肽化反应的内源性植物谷胱甘肽缀合物（GS-缀合物）很少被报道。此外，GST 通常表现出高底物的混杂性，并且它们被提议的底物容易与 GSH 发生自发的化学反应；因此，单个基因敲除很少能提供明确的化学型或表型。在少数情况下，GS-缀合物被证明是生物合成中间体，它们迅速进一步代谢为途径终产物，这解释了它们的低丰度和罕见检测。在这篇综述中，我们总结了目前对植物 GST 功能的认识，以及进化如何导致植物 GST 家族的广泛扩张，以及可能的原因。最后，我们证明内源性 GS-缀合物在植物中比想象的更为普遍，并提出它们被忽视作为鉴定植物 GST 功能的线索。本文是“植物代谢进化”主题特刊的一部分。
