Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, 310008, Zhejiang, China; Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Hangzhou, 310008, Zhejiang, China.
Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, 310008, Zhejiang, China; Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Hangzhou, 310008, Zhejiang, China.
Phytochemistry. 2021 Jan;181:112588. doi: 10.1016/j.phytochem.2020.112588. Epub 2020 Nov 21.
Plant polyphenol oxidases (PPOs) are ubiquitous copper metalloenzymes with a biochemistry that has been known for more than a century. By the 1990s, biologists began to recognize the importance of PPOs in plant response to the infestation of herbivores and pathogens; ideas concerning a defensive role for PPOs arose to address observed evidence, and several testable hypotheses were suggested. Two pivotal discoveries in tomato (Lycopersicon esculentum Miller) plants, an inverse correlation between PPO levels and insect growth and PPO induction by defence signals, have driven many studies of PPO defence functions in the context of abiotic and biotic stresses. During the past three decades, extensive molecular research in transgenic and non-transgenic systems has partly revealed the sophisticated mechanisms underlying PPO defence against herbivores and pathogens. These understandings, rather than theoretical predictions, have driven the development of new hypotheses and advanced PPO-related studies. Here, we review progress in PPO family features, expression regulation and the defensive role of PPOs in plants. We propose assumptions of an extended range of co- and post-transcriptional processes to the regulation of unexplored PPO expression. In addition, the identification of endogenous PPO substrates and downstream targets of PPO action will be useful for elucidating PPO defensive roles. The potential effects of PPO-mediated oxidative defences on herbivore performance ultimately needs to be further investigated. Therefore, expanding multidisciplinary approaches to unexplored dimensions of PPO defence function should be a future priority.
植物多酚氧化酶（PPOs）是一种普遍存在的铜金属酶，其生物化学性质已经为人所知超过一个世纪。到 20 世纪 90 年代，生物学家开始认识到 PPO 在植物对草食动物和病原体侵害的反应中的重要性；关于 PPO 在植物防御中的作用的观点出现了，以解决观察到的证据，并提出了几个可测试的假设。番茄（Lycopersicon esculentum Miller）植物中的两个关键发现，PPO 水平与昆虫生长之间的反比关系和防御信号诱导 PPO 的诱导，推动了许多关于 PPO 在非生物和生物胁迫下防御功能的研究。在过去的三十年中，在转基因和非转基因系统中的广泛分子研究部分揭示了 PPO 防御草食动物和病原体的复杂机制。这些理解，而不是理论预测，推动了新假设的发展和 PPO 相关研究的进展。在这里，我们回顾了 PPO 家族特征、表达调控以及 PPO 在植物中的防御作用的研究进展。我们提出了假设，即在转录后和翻译后过程中存在扩展范围的调控，以调节未被探索的 PPO 表达。此外，鉴定内源性 PPO 底物和 PPO 作用的下游靶标将有助于阐明 PPO 的防御作用。PPO 介导的氧化防御对草食动物性能的潜在影响最终需要进一步研究。因此，扩大多学科方法以探索 PPO 防御功能的未知维度应该是未来的优先事项。
