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压力是一个重要的研究目标。本提案描述了一项关于杨树（统称为杨树）生化适应性的研究计划。杨树已成为分子生物学和基因组学研究的典范树种。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，特别是浓缩单宁。这些是聚合类黄酮，也被称为原花青素，它可以构成高达25%的杨叶干重。缩合单宁是植物界中分布最广泛的次生代谢物，在木本植物中非常普遍。杨树还能制造水杨科植物所特有的水杨酸类酚苷，其生物合成方法尚不清楚。这两类酚类物质都有助于杨树适应环境。酚类苷被确定为有效的昆虫防御，而缩合单宁的作用似乎更广泛。***本研究的目的是确定杨树酚类植物化学物质，特别是单宁的合成是如何被调节的，以及这些化学物质如何促进树木的适应。在杨树中，单宁受胁迫诱导。我们之前的研究表明，这种诱导是受转录调控的，并发现了一种转录因子MYB134，可以刺激杨树浓缩单宁的合成。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抑制蛋白样蛋白。我们假设这些抑制因子可以微调单宁和类黄酮的合成。拟议的研究将调查这些MYB抑制因子的功能，并确定它们如何相互作用以形成一个调控网络。同时，我们将研究杨树中单宁的功能。虽然有许多关于单宁在抵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压力的耐受性。在这里，我们将测试浓缩单宁在非生物胁迫耐受性中发挥作用的想法，利用我们的转基因杨树套件改变单宁水平。进一步的目的是剖析水杨酸类酚苷的生物合成。我们最近已经确定了合成它们所需的一种酶的基因，我们将用这个基因作为探针来解剖通路的其余部分。***这项研究的结果可以直接应用于其他树木，其中许多树木积累高浓度的单宁。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很重要。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得了解它们的调节对人类健康很重要。**

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. **