Iron and Light Limitation in Ecologically Important Polar Diatoms: Comparative Transcriptomics and Development of Molecular Indicators

由于地球气候变暖，南极洲周围的南大洋正在迅速变化。这些变化无疑将通过改变影响其生长和组成的条件，影响初级生产者（食物链底部的生物，特别是利用阳光作为能量的植物类生物）的群落。由于浮游植物等初级生产者在全球生物地球化学循环中发挥着重要作用，因此了解它们如何应对环境变化至关重要。在南大洋的某些地区，浮游植物的生长受到在空间和时间上变化的化学和物理性质的陡峭梯度的限制。光和铁已被确定为影响南极水域浮游植物丰度和分布的关键变量。被称为硅藻的微小藻类是浮游植物和海冰群落的主要成员，占初级生产的很大比例。本项目的总体目标是确定极性硅藻对不同光和铁条件的生理反应的分子基础。该项目应提供一种手段，评价这些因素调节南极水域硅藻生长和影响群落净生产力的程度。该项目还将进一步实现国家科学基金会的目标，即让公众获得科学发现，并培养新一代的科学家。它将通过将研究目标转化为中学生易于获取的教材，促进与极地有关的主题的教与学。该项目还将提供资金，使一名研究生和几名本科生在现代生物学的技术和观点方面得到培训。尽管许多研究已经调查了极地硅藻如何受到不同光和铁的影响，但导致其独特生理反应的细胞机制仍然未知。利用比较转录组学，最近从南极水域分离并在不同铁和辐照条件下生长的几种生态重要的极地硅藻的关键基因表达模式和代谢途径将被检查。此外，通过鉴定铁和光反应基因，将在这些极性硅藻中开发铁和光限制的分子指标，这些基因的表达模式可用于确定其生理状态。在实验室培养中验证后，这些指标将通过超转录组测序的方式来检查南极半岛西部水域沿环境梯度收集的天然硅藻组合中的铁和光限制。为了充分了解浮游植物在南大洋生物地球化学循环中的作用，提供一种可靠的方法来阐明浮游植物在任何时间和地点的生理状态是必不可少的。

The Southern Ocean surrounding Antarctica is changing rapidly in response to Earth's warming climate. These changes will undoubtedly influence communities of primary producers (the organisms at the base of the food chain, particularly plant-like organisms using sunlight for energy) by altering conditions that influence their growth and composition. Because primary producers such as phytoplankton play an important role in global biogeochemical cycling, it is essential to understand how they will respond to changes in their environment. The growth of phytoplankton in certain regions of the Southern Ocean is constrained by steep gradients in chemical and physical properties that vary in both space and time. Light and iron have been identified as key variables influencing phytoplankton abundance and distribution within Antarctic waters. Microscopic algae known as diatoms are dominant members of the phytoplankton and sea ice communities, accounting for significant proportions of primary production. The overall objective of this project is to identify the molecular bases for the physiological responses of polar diatoms to varying light and iron conditions. The project should provide a means of evaluating the extent these factors regulate diatom growth and influence net community productivity in Antarctic waters. The project will also further the NSF goals of making scientific discoveries available to the general public and of training new generations of scientists. It will facilitate the teaching and learning of polar-related topics by translating the research objectives into readily accessible educational materials for middle-school students. This project will also provide funding to enable a graduate student and several undergraduate students to be trained in the techniques and perspectives of modern biology. Although numerous studies have investigated how polar diatoms are affected by varying light and iron, the cellular mechanisms leading to their distinct physiological responses remain unknown. Using comparative transcriptomics, the expression patterns of key genes and metabolic pathways in several ecologically important polar diatoms recently isolated from Antarctic waters and grown under varying iron and irradiance conditions will be examined. In addition, molecular indicators for iron and light limitation will be developed within these polar diatoms through the identification of iron- and light-responsive genes -- the expression patterns of which can be used to determine their physiological status. Upon verification in laboratory cultures, these indicators will be utilized by way of metatranscriptomic sequencing to examine iron and light limitation in natural diatom assemblages collected along environmental gradients in Western Antarctic Peninsula waters. In order to fully understand the role phytoplankton play in Southern Ocean biogeochemical cycles, dependable methods that provide a means of elucidating the physiological status of phytoplankton at any given time and location are essential.