Evolutionary and Ecological Aspects of Plant Selenium Hyperaccumulation

摘要硒的过度积累是一种有趣的现象，某些植物物种积累这种有毒元素的浓度非常高(高达干重的0.6%)，即使在低硒土壤中也是如此。这个项目的目标是深入了解植物Se超积累可能进化的原因，以及这一特征对超积累植物生境中其他物种的影响。总体假设是：(1)Se显著影响超积累植物与草食动物之间的相互作用。由于硒介导的威慑和毒性，硒保护植物免受一般无脊椎动物和脊椎动物食草性疾病的侵害(基于初步结果)。另一方面，专业的耐硒草食动物可能已经进化，进而积累了硒，影响了更高的营养水平。(2)由于超积累植物只存在于富硒土壤中，因此硒对超积累植物与非积累植物的竞争能力是必不可少的。这些假说将使用两个超积累植物，双硫化黄芪和新铁杉，与当地相关的非积累植物物种进行比较，使用操纵性田间实验、田间调查和实验室研究相结合的方法来验证这些假设。其具体目标是确定：(1)Se是否保护超积累植物免受田间无脊椎动物和脊椎动物草食的伤害；(2)不同Se形态在保护植物免受无脊椎动物草食的影响方面的相对有效性；(3)Se超积累对草食和Se的响应的可塑性；(4)无脊椎动物对Se的耐性和积累，以及草食动物Se的积累如何影响下一营养水平；(5)超积累植物如何影响邻近非积累植物的生长，以及它们在有或没有Se的土壤中的竞争作用。金属超积累生态学的新兴研究领域有望揭示令人兴奋的生物现象。这项研究将阐明植物中Se过度积累的进化和生态，这是一个令人着迷的生理过程，目前仍知之甚少。这项研究将从分子到生态系统扩展我们关于超积累的知识：从与硒相关的基因表达对草食的响应，不同的硒化合物对草食的有效性，到超积累-草食-捕食者相互作用的研究。植物体内Se的积累也具有重要的经济后果和应用价值。过度积累的“疯草”会造成牲畜的重大损失，也可能影响濒危野生动物。硒是一种环境污染物，植物修复为解决硒问题提供了一种有吸引力的清除策略。另一方面，硒是一种必不可少的营养物质和强大的抗癌物质，富硒饮食已被证明可以改善人和动物的健康。更好地了解控制植物Se积累的因素可能有助于培育具有Se积累或耐性改变的植物。这类植物可用于硒的植物修复或作为强化食品。了解植物Se积累如何影响无脊椎动物的生长和存活，以及识别Se专家取食者，可用于控制无脊椎动物害虫和积累Se的“疯草”种群。该项目将培养研究生和本科生以及高中生。

SummarySelenium hyperaccumulation is the intriguing phenomenon that certain plant species accumulate extraordinary concentrations of this toxic element (up to 0.6% of dry weight), even from low-Se soils. The goal of this project is to obtain insight into why plant Se hyperaccumulation may have evolved, and the consequences of this trait for other species in hyperaccumulator habitats. The overall hypotheses are: (1) Se significantly affects interactions between hyperaccumulator plants and herbivores. Se protects plants from general invertebrate and vertebrate herbivory due to Se-mediated deterrence and toxicity (based on preliminary results). On the other hand, specialist Se-tolerant herbivores may have evolved that in turn accumulate Se, affecting higher trophic levels. (2) Selenium is essential for the capacity of hyperaccumulator plants to compete with nonaccumulator species, since hyperaccumulators are only found on Se-rich soils. These hypotheses will be tested using the two hyperaccumulator species, Astragalus bisulcatus and Stanleya pinnata, in comparison with related local nonaccumulator species, using a combination of manipulative field experiments, field surveys, and laboratory studies. The specific objectives are to determine: (1) whether Se protects hyperaccumulator plants from invertebrate and vertebrate herbivory in the field; (2) the relative effectiveness of different Se forms in protecting plants from invertebrate herbivory; (3) the plasticity of Se hyperaccumulation in response to herbivory and Se; (4) Se tolerance and accumulation in invertebrate herbivores and how herbivore Se accumulation affects the next trophic level; (5) how hyperaccumulator plants affect growth of neighboring nonaccumulator plant species, and their competitive interactions in soil with or without Se. The emerging research area of metal hyperaccumulation ecology promises to reveal exciting biological phenomena. This study will shed light on the evolution and ecology of Se hyperaccumulation in plants, a fascinating physiological process that is still poorly understood. This study will extend our knowledge of hyperaccumulation across the biological hierarchy from molecules to ecosystems: from Se-related gene expression in response to herbivory and the effectiveness of different selenocompounds on herbivory to the study of hyperaccumulator-herbivore-predator interactions. Se accumulation in plants also has substantial economic consequences and applications. Hyperaccumulating "locoweeds" cause significant losses in livestock and may also affect endangered wildlife. Selenium is an environmental pollutant, and phytoremediation offers an attractive cleanup strategy for the Se problem. On the other hand, Se is an essential nutrient and powerful anti-carcinogen, and Se-enriched diets have been shown to improve human and animal health. A better understanding of the factors controlling plant Se accumulation may help develop plants with altered Se accumulation or tolerance. Such plants may be useful for Se phytoremediation or as fortified foods. Knowledge of how plant Se accumulation affects growth and survival of invertebrates, and identification of Se-specialist feeders may be used to control both populations of invertebrate pests and of Se-accumulating "locoweeds". The project will train graduate and undergraduate students as well as high school students.