RUI Collaboraitve Research: Mechanisms of induced pathogen resistance in seagrasses

海草容易受到迷路菌门(迷路菌门)内形成网的原生生物的攻击。这些无处不在的、主要是腐生或寄生的生物体可以周期性地成为致命的病原体，导致牧草消耗性疾病，并导致种群突然下降。这些科学家认为，由于不断变化的环境条件改变了海草通过莽草酸/苯丙烯(SA/PP)途径产生酚类化合物来维持或发展抗病能力的能力，海草种群对迷宫攻击的敏感度出现了差异。海草叶片和枝条中酚类化合物的浓度是唯一与抗病有关的特征。以前的研究表明，对某些物种来说，抗病性与酚酸和其他多聚酚类物质的含量有关，迷宫攻击和/或伤害可以诱导酚类物质的产生，海草酚类物质在培养中抑制这种病原菌的生长。虽然海草酚类物质和抗病能力之间存在联系的证据是相关的，而且来自对少数物种的相对较少的研究，但它表明，海草像迄今研究过的所有陆地植物一样，表现出对病原体攻击的诱导防御。证据还表明，海草的反应涉及SA/PP途径的激活，导致植物酚类物质的产生。然而，SA/PP途径的调控尚未在海草中得到研究，我们也不完全了解环境因素如何影响海草的抗病能力。Arnold、Boettcher和Tanner博士将研究SA/PP途径的调节以及海草对迷宫真菌感染的抵抗力。具体地说，该研究的目标是：(1)检验关键的SA/PP途径酶被迷宫攻击诱导的假设，(2)确定SA/PP途径诱导过程中哪些酚类物质积累，(3)在体内测试酚酸/缩合单宁水平与海草抗性之间的关系，(4)确定SA/PP途径的诱导和酚类化合物的积累是否受特定环境条件的影响，以及(5)测试这些条件、SA/PP代谢的改变和海草对迷路攻击的抗性变化之间的关系。这些问题将在热带/亚热带海草地中海藻和温带海草Zostera marina这两个物种的中生体种群中得到解决，这两个物种都容易发生周期性的消耗性疾病暴发，并表现出对病原体攻击和/或伤害的诱导产生酚类化合物。在感染和未感染病原菌的植物中，将检测SA/PP途径酶的活性、酚酸和多聚酚的浓度以及生理健康指标(生长、光合作用、碳水化合物和蛋白质的浓度)。他们还将比较这些海草在不同环境条件下对感染的反应。最后，将使用特定SA/PP途径酶的人工抑制剂来确定植物在无法产生SA/PP酚类物质时抵抗迷宫攻击的能力。

Seagrasses are susceptible to attack by net-forming protists within the genusLabyrinthula (Phylum Labyrinthulomycota). These ubiquitous, largely saprophytic orweakly parasitic organisms can periodically become virulent pathogens, causing theseagrass wasting disease and contributing to sudden population declines. These scientists suggest that differences in susceptibility of seagrass populations to Labyrinthula attack arise as changing environmental conditions alter the ability of seagrasses to maintain or develop disease resistance by the production of phenolic compounds via the shikimic acid /phenylpropenoid (SA/PP) pathway. The concentrations of phenolic compounds in seagrass leaves and shoots are the only characteristics that have been linked with resistance to the wasting disease. Previous studies indicate that, for certain species, disease resistance is correlated with the contentof phenolic acids and other polymeric phenolics, that phenolic production can be induced by Labyrinthula attack and/or wounding, and that seagrass phenolics inhibit the growth of this pathogen in culture. While the evidence for a link between seagrass phenolics and disease resistance is correlative and comes from relatively few studies on a limited number of species, it indicates that seagrasses, like all terrestrial plants examined to date, exhibit induced defenses against pathogen attack. The evidence also suggests that seagrass responses involve activation of the SA/PP pathway leading to the production of plant phenolics. However, the regulation of the SA/PP pathway has not yet been examined in seagrasses, and we do not fully understand how environmental factors may affect disease resistance in seagrasses. Drs. Arnold, Boettcher and Tanner will investigate the regulation of the SA/PPpathway and the resistance of seagrasses to infection by Labyrinthula. Specifically, thegoals of the research are: (1) to test the hypothesis that key SA/PP pathwayenzymes are induced by Labyrinthula attack, (2) to determine which phenolicsaccumulate in response to SA/PP pathway induction, (3) to test, in vivo, the link between phenolic acid / condensed tannin levels and seagrass resistance, (4) to determine whether SA/PP pathway induction and the accumulation of phenolic compounds are affected by specific environmental conditions, and (5) to test the proposed link between these conditions, altered SA/PP metabolism and changes in seagrass resistance to Labyrinthula attack. These questions will be addressed in mesocosm populations of two species, the tropical/subtropical seagrass Thalassia testudinum and the temperate seagrass Zostera marina, both of which are subject to periodic wasting disease outbreaks and exhibit induced production of phenolic compounds in response to pathogen attack and/or wounding. Activities of SA/PP pathway enzymes, concentrations of phenolic acids and polymeric phenols, and indicators of physiological health (growth, photosynthesis, concentrations of carbohydrates and proteins) will be examined in infected and pathogen-free plants. They will also compare the responses of these seagrasses to infection underdifferent environmental conditions. Finally, artificial inhibitors of specific SA/PPpathway enzymes will be used to determine the ability of plants to resist Labyrinthulaattack when they are unable to produce SA/PP phenolics.