Institute of Life Sciences, Scuola Superiore Sant'Anna, Pisa, Italy.
Biology Department, University of Pisa, Pisa, Italy.
J Exp Bot. 2019 Mar 27;70(6):1815-1827. doi: 10.1093/jxb/erz052.
Ethanol fermentation is considered as one of the main metabolic adaptations to ensure energy production in higher plants under anaerobic conditions. Following this pathway, pyruvate is decarboxylated and reduced to ethanol with the concomitant oxidation of NADH to NAD+. Despite its acknowledgement as an essential metabolic strategy, the conservation of this pathway and its regulation throughout plant evolution have not been assessed so far. To address this question, we compared ethanol fermentation in species representing subsequent steps in plant evolution and related it to the structural features and transcriptional regulation of the two enzymes involved: pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH). We observed that, despite the conserved ability to produce ethanol upon hypoxia in distant phyla, transcriptional regulation of the enzymes involved is not conserved in ancient plant lineages, whose ADH homologues do not share structural features distinctive for acetaldehyde/ethanol-processing enzymes. Moreover, Arabidopsis mutants devoid of ADH expression exhibited enhanced PDC activity and retained substantial ethanol production under hypoxic conditions. Therefore, we concluded that, whereas ethanol production is a highly conserved adaptation to low oxygen, its catalysis and regulation in land plants probably involve components that will be identified in the future.
乙醇发酵被认为是高等植物在厌氧条件下确保能量产生的主要代谢适应之一。沿着这条途径，丙酮酸脱羧并被还原为乙醇，同时 NADH 被氧化为 NAD+。尽管它被认为是一种重要的代谢策略，但到目前为止，还没有评估这条途径在植物进化过程中的保守性及其调控。为了解决这个问题，我们比较了代表植物进化后续步骤的物种中的乙醇发酵，并将其与涉及的两种酶（丙酮酸脱羧酶 (PDC) 和醇脱氢酶 (ADH)）的结构特征和转录调控联系起来。我们观察到，尽管在遥远的门中缺氧时都具有产生乙醇的保守能力，但在古老的植物谱系中，涉及的酶的转录调控并不保守，其 ADH 同源物不具有乙醛/乙醇处理酶特有的结构特征。此外，缺乏 ADH 表达的拟南芥突变体在缺氧条件下表现出增强的 PDC 活性，并保留了大量的乙醇产生。因此，我们得出结论，虽然乙醇产生是对低氧的高度保守适应，但在陆地植物中，其催化和调控可能涉及未来将被识别的成分。
