Quinate, Focal Point of Upstream Metabolism Leading to Lignin

9728619延森和邦纳奎宁酸是生物圈中含量最丰富的天然产物之一。它在木本植物的一些组织中积累，例如新形成的针叶，其数量相当于总干重的10%。奎尼酸作为一种具有不同代谢命运的中间体，具有极高的活性。在木质部形成细胞中，它主要转化为木质素的苯丙醇前体。另一方面，在自养细胞中，奎宁酸是其他酚类化合物的有效前体--最值得注意的是绿原酸、没食子酸和原儿茶酸。绿原酸和没食子酸对食草动物捕食和植物病原微生物具有抵抗力。原儿茶酸被分解为中心中间体，在暗代谢过程中可作为碳源储备。最后，奎尼酸是一种高度溶解、易于运输的代谢物，可以作为芳香氨基酸在不同组织中的多种前体。火炬松(Pinus Taeda)这一实验系统正在被其他人深入研究，以了解和操纵木质素的含量。因此，许多生物和分子遗传资源可用于支持这一项目，包括木质素诱导的组织培养系统。这项研究的目的是阐明将L-苯丙氨酸输送到苯丙氨酸代谢区段的上游接口代谢的性质。它将集中在三种奎尼酸脱氢酶蛋白：在针状组织中的nQDHNADP和nQDHNAD，以及在木质部形成细胞中的xQDHNADP。NQDH-NADP似乎是三官能团，具有催化结构域，可将奎宁酸酯全部转化为原儿茶酸酯。这些酶将被提纯，用于产生特定的抗体，并对其物理和催化特性进行表征。通过免疫筛选获得与每个QDH相对应的cDNA克隆。特异性抗体将用于免疫金EM细胞定位。调控将通过监测酶活性水平、蛋白质含量和转录丰度来检查，以响应发育和环境提示。长期的目标是了解整个代谢网络是如何被差异化地调节以实现奎尼酸分子命运的动态变化的。这有望为生物技术操作提供最终合理的基础，这些操作旨在通过改变不同细胞隔室和不同专门组织中进出奎宁的通量来改变木质素的含量。

9728619 Jensen and Bonner Quinic acid is one of the most abundant natural products in the biosphere. It is accumulated in some tissues of woody plants, e.g., newly forming needles of conifers, in amounts equaling up to 10% of the total dry weight. Quinic acid is exceedingly active as an intermediate which possesses alternative metabolic fates. In xylem-forming cells it is mainly transformed to phenylpropanoid precursors of lignin. In autotrophic cells, on the other hand, quinic acid is an effective precursor of other phenolic compounds - the most noteworthy ones being chlorogenic acid, gallic acid and protocatechuic acid. Chlorogenic acid and gallic acid confer resistance to herbivore predation and phytopathogenic microorganisms. Protocatechuic acid is catabolized to central intermediates and can serve as a carbon-source reserve during dark metabolism. Finally, quinic acid is a highly soluble, readily transported metabolite which can serve as a versatile precursor of aromatic amino acids in different tissue compartments. Loblolly pine (Pinus taeda), the experimental system, is under intensive study by others in order to understand and manipulate lignin content. Therefore, many biological and molecular-genetic resources are available to support this project, including a tissue-culture system which is lignin-inducible. The goal of this research is to elucidate the nature of the interfacing upstream metabolism which delivers L-phenylalanine to the phenylpropanoid metabolic section. It will focus upon three quinate dehydrogenase proteins: nQDH-NADP and nQDH-NAD in needle tissue and xQDH-NADP in xylem-forming cells. NQDH-NADP appears to be trifunctional, having catalytic domains which carry out the overall conversion of quinate to protocatechuate. The enzymes will be purified, used to raise specific antibodies, and characterized for physical and catalytic properties. cDNA clones corresponding to each QDH will be obtained by immunoscreening. Specific antibody will be used for immunogold EM cytoloca lization. Regulation will be examined by monitoring levels of enzyme activity, amounts of protein, and transcript abundance in response to developmental and environmental cues. The longterm objective is to understand how this entire metabolic network is differentially regulated to accomplish the dynamic alternative molecular fates of quinate. This is expected to provide ultimately a rational basis for biotechnological manipulations designed to modify lignin content by alteration of flux toward and away from quinate in different cellular compartments and in different specialized tissues.