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

California State University-Fresno Foundation, Fresno CA

Investigators

Abstract

0128977 Zechman Three 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.