CAREER: Nitrogen Assimilation in Marine Algae: Evolution, Physiology, and Educational Opportunties

Clark University, Worcester MA

Investigators

Abstract

The assimilation of nitrogen into amino acids is a key process regulating the growth and productivity of photosynthetic organisms. The regulation of nitrogen assimilation has been studied extensively in vascular plants and cyanobacteria; however, only limited information is available concerning the evolution and regulation of these pathways in eukaryotic algae. The term "algae" is used to describe diverse lineages of photosynthetic organisms, many of which arose through independent secondary endosymbiotic events (symbioses between photosynthetic and non-photosynthetic eukaryotes). The incorporation of symbionts into host cells increased the genetic diversity on which natural selection could act and is assumed to have contributed significantly to the metabolic diversity observed in extant algal lineages. The independent endosymbiotic origin of photosynthetic lineages further suggests that enzymes involved in carbon and nitrogen metabolism may have arisen through different evolutionary processes (e.g., gene transfer versus gene duplication) and that regulatory pathways, which were established following the endosymbiotic events, may differ among lineages. The enzyme glutamine synthetase (GS) is essential for ammonium assimilation and glutamine biosynthesis in all organisms and is the enzymatic link between carbon and nitrogen metabolism. Multiple forms of GS are expressed in photosynthetic eukaryotes and the isoenzymes are compartmentalized in either the cytosol or chloroplast. The goals of this research program are to (1) expand our knowledge of the evolution of nitrogen assimilation in photosynthetic eukaryotes by examining the molecular evolution of GS in diverse algae lineages, (2) identify and characterize the physiological functions of GS isoenzymes in the diatom Skeletonema costatum, and (3) to examine the cellular processes that regulate GS expression in S. costatum. Diatoms are a species-rich group of organisms that contribute significantly to oceanic primary productivity and global biogeochemical cycles. This research will contribute to our understanding of mechanisms regulating nitrogen assimilation in photosynthetic eukaryotes, processes governing algal growth and oceanic productivity, and the evolution of metabolic pathways. The work will provide a framework for future studies using emerging genomic and bioinformatic tools to understand the complex and interacting pathways coupling carbon and nitrogen metabolism in photosynthetic organisms. The common thread woven throughout this project is that mentored research experiences improve knowledge generation and acquisition skills, develop critical thinking skills, and increase self-confidence in learners at all levels. This project uses several pedagogical approaches to provide new opportunities for undergraduates, graduate students, and science teachers from local public schools to participate in research-based learning activities. As part of Clark University's mission to establish partnerships with the Worcester community, this project provides summer research opportunities for middle- and high-school science teachers. This research alliance provides discipline-based training for teachers and a forum for the discussion of effective teaching practices for grades K-16. In addition, the PI will develop a new inquiry-based course in physiological ecology that offers investigative and cooperative learning experiences to undergraduates who may not have pursed mentored research opportunities. The integrated research and teaching program illustrates the PI's commitment to a career aimed at the multi-disciplinary study of algal physiology and evolution, to the development of innovative science curricula, and to community education.