Molecular and Functional Analysis of Phenolic Metabolism in Poplar

森林健康对加拿大具有重大意义。因此，了解树木如何适应环境中的压力是一个重要的研究目标。这项建议描述了一项关于杨树(统称为杨树)生化适应的研究计划。杨树已成为分子生物学和基因组学的模式树。重要的是，杨树还含有高浓度的生物活性酚类植物化学物质，特别是缩合单宁。这些是聚合物类黄酮，也被称为原花青素，它可以构成杨树叶片干重的25%。缩合单宁是植物界分布最广泛的次生代谢物，在木本植物中广泛存在。杨树还可以制造水杨素类酚苷，这是杨柳科特有的，其生物合成尚不清楚。这两类酚类物质都有助于杨树适应环境。酚苷被证明是对昆虫的有效防御，而缩合单宁的作用似乎要广泛得多。 拟议研究的目的是确定杨树酚类植物化学物质的合成，特别是单宁的合成是如何受到调控的，以及这些化学物质如何有助于树木的适应。在杨树中，单宁是受胁迫诱导的。我们以前证明了这种诱导是转录调控的，并发现了一种转录因子MYB134，它可以刺激杨树缩合单宁的合成。最近的结果表明，MYB134是单宁基因调控网络的一部分，该网络还包括至少四个MYB抑制因子样蛋白。我们推测，这些抑制物可以微调单宁和类黄酮的合成。这项拟议的研究将调查这些MYB抑制子的功能，并确定它们如何相互作用形成调控网络。同时，我们还将研究单宁在杨树中的作用。虽然有许多关于单宁在防御昆虫食草动物方面的潜在作用的研究，但最近的证据表明，它们的作用包括对其他类型的压力的耐受性。在这里，我们将利用我们的一套改变单宁水平的转基因杨树来测试缩合单宁在非生物胁迫耐受性中发挥作用的想法。另一个目标是剖析水杨苷类酚苷的生物合成。我们最近已经确定了它们合成所需的一种酶的基因，我们将使用该基因作为探针来剖析该途径的其余部分。 这项研究的结果可以直接应用于其他树木，其中许多树积累了高浓度的单宁。单宁如何影响树木健康以及更大的生态系统，对森林管理和生态都将是重要的。此外，单宁在降低心血管疾病风险方面对人类饮食的重要性使了解其调节对人类健康非常重要。

Forest health is of major significance to Canada. Understanding how trees are adapted to stresses in the environment is thus an important research aim. This proposal describes a program of research on the biochemical adaptations of Populus trees (collectively called poplars). Poplar has become a model tree for molecular biology and genomics. Importantly, poplars also contain high concentrations of bioactive phenolic phytochemicals, in particular condensed tannins. These are polymeric flavonoids, also known as proanthocyanidins, which can constitute up to 25 % of poplar leaf dry weight. Condensed tannins are the most widely distributed secondary metabolite in the plant kingdom and are very prevalent among woody plants. Poplars also make salicinoid phenolic glycosides, which are unique to the Salicaceae and whose biosynthesis is unknown. Both classes of phenolics help adapt poplar to its environment. The phenolic glycosides are established as effective defenses against insects, whereas the role of condensed tannins appears to be much broader. The aim of the proposed research is to determine how the synthesis of poplar phenolic phytochemicals, in particular of the tannins, is regulated, and how these chemicals contribute to adaptation of trees. In poplars, tannins are inducible by stress. We previously showed that this induction is transcriptionally regulated and identified a transcription factor, MYB134, that stimulates condensed tannin synthesis in poplar. Recent results indicate that MYB134 is part of a tannin gene regulatory network that also includes at least four MYB repressor-like proteins. We hypothesize that these repressors can fine-tune tannin and flavonoid synthesis. The proposed research will investigate the functions of these MYB repressors, and determine how they interact to form a regulatory network. In parallel, we will investigate the functions of tannins in poplar. While there are many studies on the potential role of tannins in defense against insect herbivores, recent evidence suggests their role includes tolerance to other types of stresses. Here we will test the idea that condensed tannins play a role in abiotic stress tolerance, making use of our suite of transgenic poplars with altered tannin levels. A further objective is to dissect the biosynthesis of the salicinoid phenolic glycosides. We have recently identified a gene for an enzyme that is required for their synthesis, and we will use this gene as a probe to dissect the rest of the pathway. The results of this research can be applied directly to other trees, many of which accumulate high concentrations of tannin. How tannins affect tree health as well as the larger ecosystem will be important for both forest management and ecology. Furthermore, the importance of tannins to the human diet in reducing the risk of cardiovascular disease makes understanding their regulation important for human health.