Desmet Sandrien, Morreel Kris, Dauwe Rebecca
Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Gent, Belgium.
Center for Plant Systems Biology, VIB, 9052 Gent, Belgium.
Plants (Basel). 2021 Nov 6;10(11):2393. doi: 10.3390/plants10112393.
The plant specialized metabolome consists of a multitude of structurally and functionally diverse metabolites, variable from species to species. The specialized metabolites play roles in the response to environmental changes and abiotic or biotic stresses, as well as in plant growth and development. At its basis, the specialized metabolism is built of four major pathways, each starting from a few distinct primary metabolism precursors, and leading to distinct basic carbon skeleton core structures: polyketides and fatty acid derivatives, terpenoids, alkaloids, and phenolics. Structural diversity in specialized metabolism, however, expands exponentially with each subsequent modification. We review here the major sources of structural variety and question if a specific role can be attributed to each distinct structure. We focus on the influences that various core structures and modifications have on flavonoid antioxidant activity and on the diversity generated by oxidative coupling reactions. We suggest that many oxidative coupling products, triggered by initial radical scavenging, may not have a function , but could potentially be enzymatically recycled to effective antioxidants. We further discuss the wide structural variety created by multiple decorations (glycosylations, acylations, prenylations), the formation of high-molecular weight conjugates and polyesters, and the plasticity of the specialized metabolism. We draw attention to the need for untargeted methods to identify the complex, multiply decorated and conjugated compounds, in order to study the functioning of the plant specialized metabolome.
植物特化代谢组由大量结构和功能各异的代谢物组成，因物种而异。特化代谢物在植物对环境变化以及非生物或生物胁迫的响应中发挥作用，同时也参与植物的生长和发育。从根本上来说，特化代谢建立在四条主要途径之上，每条途径都从几种不同的初级代谢前体开始，生成不同的基本碳骨架核心结构：聚酮化合物和脂肪酸衍生物、萜类化合物、生物碱和酚类化合物。然而，特化代谢中的结构多样性会随着后续的每一次修饰呈指数级增长。我们在此回顾结构多样性的主要来源，并探讨是否能为每一种独特结构赋予特定功能。我们重点关注各种核心结构和修饰对黄酮类抗氧化活性的影响，以及氧化偶联反应所产生的多样性。我们认为，许多由初始自由基清除引发的氧化偶联产物可能并无功能，但有可能通过酶促作用循环转化为有效的抗氧化剂。我们还将进一步讨论由多种修饰（糖基化、酰基化、异戊烯基化）所产生的广泛结构多样性、高分子量共轭物和聚酯的形成，以及特化代谢的可塑性。我们提请注意，需要采用非靶向方法来鉴定这些复杂的、经过多重修饰和共轭的化合物，以便研究植物特化代谢组的功能。
