Collaborative Research: Molecular, Biochemical and Signal Transduction Analysis of a Phytotoxic Root-Root Communication Process Mediated by (-)-Catechin in the Rhizosphere

植物根周围的土壤被称为根际，是一种独特的物理、生化和生态环境。根际在很大程度上是由根系通过分泌到周围土壤中的化学物质来控制的。这些根分泌物（渗出物）可能在植物与其环境沟通时发挥共生或防御作用，最终对其根际其他元素产生积极或消极的反应。消极交流的一个例子是亚洲本土的马蹄莲（Centaurea maculosa L.）。半人马。（斑knapweed）是北美最具侵略性和破坏性的外来杂草之一，特别是在美国西北部的田地和牧场。尽管长期以来人们一直认为斑knapweed通过分泌一种植物毒性化学物质（化感化学物质）来获得优势地位，但直到去年才发现这种化学物质，当时确定斑knapweed根的分泌物确实对其他植物有毒。这种化学物质的活性“成分”是外消旋儿茶素，是(+)-儿茶素和(-)-儿茶素50:50的混合物。虽然(+)-儿茶素在植物界广泛存在，但(-)-儿茶素和外消旋形式都极为罕见。此外，渗出液的抗植物部分完全是由于(-)-儿茶素，而(+)-儿茶素是无活性的。相反，(+)-儿茶素对某些细菌有活性，而(-)-儿茶素则没有。（-）-儿茶素对拟南芥和多种作物有毒性，对斑点knapweed的近亲C. diffusa也有毒性。（-）-儿茶素本身不影响黄花姜幼苗和种子的萌发。在拟南芥中，斑knapweed的有毒化学物质引发了一系列快速的应激反应，杀死了根分生组织和伸长区的细胞，最终导致整个根系的死亡。拟议的研究将阐明与这种植物地下部分的消极交流过程相关的分子和生化相互作用。具体而言，本研究将研究（-)-儿茶素对拟南芥根际的负调控作用，目的如下：1)了解（-)-儿茶素在拟南芥根际引发的毒性化学过程；2）了解(-)-儿茶素解毒的机制；3）克隆(-)-儿茶素产生的相关基因。儿茶素与拟南芥等植物的相互作用是在自然土壤条件下发生的事件，因此具有生物学相关性。此外，这项研究将提供更广泛的好处，培养两名博士后学者，一名研究生和本科生在一个多学科的研究氛围。此外，该研究对美国农业和保护美国西部植物多样性具有实际意义

The soil surrounding a plant root, known as the rhizosphere, is a unique physical, biochemical and ecological environment. The rhizosphere is to a large extent controlled by the root system through chemicals secreted into the surrounding soil. These root secretions (exudates) may play symbiotic or defensive roles as a plant communicates with its environment, ultimately developing a positive or negative response to the other elements in its rhizosphere. An example of negative communication is provided by the Asian native Centaurea maculosa L. (spotted knapweed). Centaurea maculosa Lam. (spotted knapweed) is one of the most invasive and destructive introduced weeds in North America, particularly in the fields and pastures of the northwest U.S. Although it has long been proposed that spotted knapweed achieves its dominance through secretion of a plant-toxic chemical (allelochemical), no such chemical had been identified until last year, when it was determined that an exudate of spotted knapweed roots is indeed toxic to other plants. The active "ingredient" of this chemical is composed of racemic catechin, a 50:50 mixture of (+)-catechin and (-)-catechin. Although (+)-catechin is widespread throughout the plant kingdom, both (-)-catechin and the racemic form are extremely rare. Further, the anti-plant part of the exudate was entirely due to (-)-catechin, while (+)-catechin was inactive. Conversely, (+)-catechin was active against certain bacteria, while (-)-catechin was not. (-)-Catechin was found to be toxic against Arabidopsis and a variety of crop plant species and was also toxic to C. diffusa (diffuse knapweed), a close relative of spotted knapweed. (-)-Catechin did not affect seedlings or seed germination of C. maculosa itself. In Arabidopsis thaliana, spotted knapweed's toxic chemical triggers a rapid cascade of stress responses which kill cells in the root meristem and elongation zone and ultimately lead to the death of the entire root system. The proposed research will shed light on the molecular and biochemical interactions that occur in conjunction with this negative communication process in the subterranean part of this plant. Specifically, the proposal will examine the negative control exerted by (-)-catechin in the rhizosphere of C. maculosa using the following aims: 1) to understand the toxic chemical processes initiated by (-)-catechin in Arabidopsis roots, 2) to understand the mechanism by which C. maculosa detoxifies (-)-catechin, and 3) to clone the gene(s) involved in (-)-catechin production. The interaction of (-)-catechin with plants such as Arabidopsis is an event that occurs under natural soil conditions, and thus has biological relevance. In addition, this research will provide the broader benefits of training two postdoctoral scholars, one graduate student and undergraduates in a multidisciplinary research atmosphere. Furthermore, the research outlined has practical implications to both U.S. agriculture and to preserving plant diversity of the Western U.S.