Collaborative Research: A Multi-Gene Approach to Chlorophytan Phylogeny and Diversity

[128952 . 52]三个研究小组（图尔萨大学的Buchheim，北达科他州立大学的Fawley和弗雷斯诺加州州立大学的Zechman）已经开始了一项合作，将解决绿藻群之间的等级（即系统发育）关系的问题，这些绿藻群统称为绿藻。绿藻在林奈命名系统中具有门的地位，是绿色植物谱系的两个分支之一，另一个分支是陆生植物联盟。绿藻包括从微观到宏观的生物，表现出多种繁殖策略（例如，有性或无性），并生活在广泛的栖息地（例如，淡水，咸水和陆地）。目前主要基于比较形态学的绿藻分类方案的某些方面已受到来自比较分子数据的新证据的挑战。然而，对新证据的全面解释尚未出现，因为：(1)这些新的分子数据并未应用于绿藻内的所有类群；(2)在大多数情况下，仅使用单个基因来评估选定的绿藻类群之间的多样性（不像陆地植物，某些类群的多样性研究使用了三个或更多不同的基因）。本项目的目的是通过比较3种不同基因的DNA序列数据，即核18S核糖体RNA和26S核糖体RNA基因，以及叶绿体rbcL基因，对绿藻多样性进行综合评估。这两个rRNA基因编码活细胞中发现的所有核糖体的部分。rbcL基因是叶绿体基因组的一部分，编码植物中负责固定碳的酶的一部分。加州州立大学弗雷斯诺分校的泽赫曼实验室将负责收集绿藻群（即Ulvophyceae）的数据。北达科他州立大学的福利实验室小组将负责收集被称为绿藻门的绿藻组的数据。图尔萨大学的布赫海姆实验室小组将从两个绿藻组——绿藻科和绿藻科——收集数据。该项目最终将完成(1)对所有绿藻分子数据的系统发育综合，(2)对绿藻分类进行基本的重新评估，整合形态和光合色素数据，以及(3)将绿藻分子系统发育数据与（已发表的）陆地植物谱系的平行数据整合。使用绿藻作为模式生物的研究（例如，很容易在实验室培养的衣藻属）大大提高了我们对光合作用和鞭毛功能等基本过程的理解。随着生物学家继续剖析生物现象的分子和生化基础，新的叶绿素模型将被探索，以了解与这些现象相关的变异谱。更全面地了解所有绿藻群之间的关系对于解释作为模式生物的绿藻研究的结果（例如，评估更广泛的适用性）将是至关重要的。此外，对绿藻多样性的综合评估结果将为未来依赖绿藻模拟机制的生物过程研究提供信息。最后，对绿藻多样性的研究对于促进我们对绿色植物谱系起源和进化的理解至关重要。

0128952FawleyThree research teams (Buchheim at University of Tulsa, Fawley at North Dakota State University, and Zechman at California State University at Fresno) have begun a collaboration that will address questions about the hierarchical (i.e., phylogenetic) relationships among green algal groups that are collectively known as the Chlorophyta. The Chlorophyta, which has phylum status in the Linnean nomenclatural system, represents one of two branches of the green plant lineage-the other branch being the land plant alliance. The Chlorophyta comprise organisms that range from the microscopic to the macroscopic, exhibit a variety of reproductive strategies (e.g., sexual vs. asexual), and live in a broad spectrum of habitats (e.g., freshwater, saltwater and terrestrial). Some aspects of the current classification scheme for the Chlorophyta, based largely on comparative morphology, have been challenged by new evidence from comparative molecular data. A comprehensive interpretation of the new evidence, however, has not been forthcoming because (1) these new molecular data have not been applied to all groups within the Chlorophyta and (2) in most cases only a single gene has been used to evaluate diversity among select groups of Chlorophyta (unlike the land plants where diversity in some groups has been studied using three or more different genes). The goal of this project is to develop a comprehensive assessment of diversity in the Chlorophyta using a comparative study of DNA sequence data in three different genes, the nuclear 18S ribosomal RNA and 26S ribosomal RNA genes, and the chloroplast rbcL gene. The two rRNA genes code for portions of all ribosomes found in living cells. The rbcL gene is part of the chloroplast genome and codes for a portion of the enzyme responsible for carbon fixation in plants. The Zechman lab at CSU-Fresno will be responsible for gathering data from the chlorophyte group known as the Ulvophyceae. The Fawley lab group at North Dakota State University will be responsible for gathering data from the chlorophyte group known as the Prasinophyceae. The Buchheim lab group at the University of Tulsa will gather data from the two chlorophyte groups, Trebouxiophyceae and Chlorophyceae. The project will culminate in (1) a phylogenetic synthesis of all molecular data for the Chlorophyta, (2) a fundamental re-assessment of chlorophyte classification, integrating morphological and photosynthetic pigment data, and (3) an integration of the chlorophyte molecular phylogenetic data with (published) parallel data from the land plant lineage. Studies using chlorophyte green algae as model organisms (for example, the genus Chlamydomonas, easily cultured in the laboratory) have significantly advanced our understanding of fundamental processes such as photosynthesis and flagellar function. As biologists continue to dissect the molecular and biochemical basis for biological phenomena, new chlorophyte models will be explored in order to understand the spectrum of variation associated with these phenomena. A more comprehensive understanding of the relationships among all chlorophyte groups will be vital to interpreting the results (for example, assessing the broader applicability) from studies of chlorophytes used as model organisms. Moreover, the results from a comprehensive assessment of chlorophyte diversity will inform future studies of biological processes that rely on green algae to model the mechanisms. Lastly, studies of diversity within the Chlorophyta are critical to advancing our understanding of the origins and evolution of the green plant lineage.