The Betalain Secondary Metabolic Network

几乎所有的开花植物，如玫瑰、玉米和枫树，都会产生色素，使花朵、果实和叶子呈红色或紫色。几乎所有这些红色色素都是由一种叫做苯丙氨酸的氨基酸制成的“花青素”。有一个明显的例外，那就是一组密切相关的开花植物，包括甜菜、仙人掌和苋菜，它们不产生花青素，而是从氨基酸酪氨酸中产生红色和黄色的“甜菜素”色素。和花青素一样，甜菜素也是重要的膳食抗氧化剂，在许多方面对植物和人类健康都有贡献。该项目旨在了解植物基因表达和植物细胞结构如何协调合成甜菜素色素，然后将其传递到植物细胞储存室液泡。红色和黄色甜菜素色素可以在非甜菜素物种中产生，如酵母和花青素生产植物，通过甜菜素合成基因的表达。因此，有可能生产出具有更高营养价值的改良微生物和作物，从而造福人类和动物。此外，由于这个项目是如此“丰富多彩”，它自然吸引了那些想要从事分子生物学和生物技术相关职业的本科生。该项目每年将培养35名大学新生进行下一代分子遗传学研究。研究人员最近发现了一种新的β -生物合成细胞色素P450酶，其功能是从酪氨酸中产生LDOPA和环dopa（所需的中间体），以及一种myb型转录因子，该转录因子激活编码这些酶的基因。剩下的关键知识缺口包括：基因调控如何影响β素色素模式和环境反应；β素色素如何被运输到/穿过液泡膜；甜菜素植物为什么以及如何避免产生花青素——这种互斥性是这一重要植物群的基本特性。在这个项目中，我们将利用功能的损失和获得来研究甜菜MYB，以了解其在甜菜基因组中的直接和间接靶点网络。目前还不清楚β素是如何被运送到中央储存液泡的。研究人员将进行抑制剂研究和神经质体蛋白质组学研究，以测试运输假设、潜在机制和识别相关蛋白质。最后，目前尚不清楚为什么或如何积累甜菜素的植物不能或不产生花青素。单宁途径在化学上与花青素密切相关，直到最后一步都有共同的中间产物，它们都由组合MYB-bHLH-WD转录因子复合物的版本调节。积累甜菜素的植物确实会产生单宁酸，研究人员将在培育甜菜种皮的过程中描述单宁酸途径的特征，他们将尝试在转基因甜菜根中重建花青素途径，以测试关于哪些步骤缺失的假设。

Virtually all flowering plants, like roses, maize, and maple trees, make pigments to color flowers, fruits, and leaves red or purple. And almost all of these red pigments are "anthocyanins" made from an amino acid called phenylalanine. There is one glaring exception to this in a group of closely related flowering plants that includes beets, cactus, and amaranthus, that don't make anthocyanins, but instead make red and yellow "betalain" pigments from the amino acid tyrosine. Like anthocyanins, betalains are important dietary antioxidants that contribute to plant and human health in many ways. This project is aimed at understanding how plant gene expression and plant cellular structures coordinate to synthesize the betalain pigments and then deliver them to the plant cell storage compartment called the vacuole. The red and yellow betalain pigments can be produced in non-betalain species, like yeast and anthocyanin producing-plants, through the expression of betalain-synthesizing genes. So it will be possible to produce modified microbes and crops with enhanced nutritional value for the benefit of people and animals. In addition, because this project is so "colorful" it is a natural draw for undergraduate students who want to pursue molecular biology and biotechnology-based careers. This project will train a cohort of 35 college freshmen each year in next-generation molecular-genetic research.The investigators recently identified novel, betalain-biosynthetic cytochrome P450 enzymes that function to produce LDOPA and cyclo-DOPA (required intermediates) from tyrosine, and a MYB-type transcription factor that activates the genes encoding these enzymes. Remaining critical knowledge gaps include: how gene regulation impacts betalain pigment patterning and environmental response; how betalain pigments are trafficked to/across the tonoplast (vacuole membrane); why and how betalain plants avoid making anthocyanins--this mutual exclusivity being a fundamental property in this important group of plants. In this project, the beet MYB will be investigated using loss and gain of function studies to understand its network of direct and indirect targets in the beet genome. Nothing is known about how betalains are transported to the central storage vacuole. The investigators will perform inhibitor studies and tonoplast proteomic studies to test transport hypotheses, potential mechanisms, and identify associated proteins. Finally, it is not known why or how betalain accumulating plants can't or don't make anthocyanins. The tannin pathway is closely related to the anthocyanins chemically, with common intermediates up until the very last steps, and they are both regulated by versions of the combinatorial MYB-bHLH-WD transcription factor complex. Betalain accumulating plants do make tannins and the investigators will characterize the tannin pathway in developing beet seed coats, and they will attempt to recreate the anthocyanin pathway in transgenic beet roots to test hypotheses about which steps are missing.