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。该提案描述了一个关于杨树（统称杨树）生物化学适应性的研究计划。白杨已成为分子生物学和基因组学研究的模式树种。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。这些是聚合类黄酮，也称为原花色素，其可以构成高达25%的白杨叶干重。缩合单宁是植物界分布最广的次生代谢产物，在木本植物中非常普遍。杨树也能产生水杨酸酚苷，这是杨柳科独有的，其生物合成尚不清楚。这两类酚类物质有助于白杨适应环境。酚苷被确立为有效的防御昆虫，而缩合单宁的作用似乎要广泛得多。 拟议的研究的目的是确定如何合成的白杨酚类植物化学物质，特别是单宁，调节，以及这些化学物质如何有助于适应树木。在杨树中，单宁是由压力诱导的。我们以前表明，这种诱导是转录调控，并确定了一个转录因子，MYB134，刺激缩合单宁在白杨的合成。最近的研究结果表明，MYB134是单宁基因调控网络的一部分，该网络还包括至少四种MYB阻遏物样蛋白。我们推测这些阻遏物可以微调单宁和类黄酮的合成。拟议的研究将调查这些MYB阻遏物的功能，并确定它们如何相互作用以形成调控网络。同时，我们将研究单宁在白杨中的功能。虽然有许多关于单宁在防御昆虫食草动物中的潜在作用的研究，但最近的证据表明它们的作用包括对其他类型压力的耐受性。在这里，我们将测试的想法，缩合单宁发挥作用，在非生物胁迫耐受性，利用我们的一套转基因杨树与改变单宁水平。另一个目标是剖析水杨酸酚苷的生物合成。我们最近发现了一个合成它们所需的酶的基因，我们将用这个基因作为探针来分析剩下的通路。 这项研究的结果可以直接应用于其他树木，其中许多树木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将是重要的森林管理和生态。此外，单宁对人类饮食在降低心血管疾病风险方面的重要性使得了解它们的调节对人类健康至关重要。

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.