Cellular Basis of Novel Organelle Integration by a Photosynthetic Animal

PROJECT SUMMARY / ABSTRACT Endosymbiotic events have driven the evolution of dramatic and consequential biological traits, however most known examples occurred billions of years ago, resulting in deeply integrated associations that mask early steps in the evolution of these associations. “Solar powered, sap sucking” Sacoglossan sea slugs represent a recent and incompletely established endosymbiosis in which stolen, functional chloroplasts are stored in slug tissues. Here, I propose to leverage this unique organism to understand the mechanistic basis of stolen chloroplast (kleptoplast) retention and integration into host cell physiology as a model for understanding endosymbiosis more broadly. To accomplish this, I will: (Aim 1) use organellar proteomics to identify proteins critical for establishment and maintenance of this endosymbiosis (often called “functional kleptoplasty”), (Aim 2) determine the function of those proteins using a combination of pharmacology, patch clamp experiments, and heterologous expression studies, and finally (Aim 3) expand these experiments in a comparative approach using different species of Sacoglossan slugs with different retention abilities. Thus, this study will employ rigorous methodology combining state-of-the-art sequencing technology and multi-omics approaches with physiological approaches, functional assays, and a diverse set of imaging techniques. Further, I will leverage the incredible biodiversity of sea slugs to empower a comparative approach for a comprehensive understanding of a truly unique biological phenomenon: the maintenance of functional photosynthetic chloroplasts within animal tissues. This project will take place at host institution Harvard Medical School (HMS, Cell Biology) and builds on my expertise in transcriptomics, evolutionary biology, and bioinformatics with training in new skills from my primary sponsor, Dr. Corey Allard (HMS, Cell Biology), in electrophysiology, biochemistry, and molecular techniques. I will be aided by an interdisciplinary advisory team composed of my co-sponsor, Dr. Wade Harper (HSM, Cell Biology), an expert in organelle proteomics, Dr. Steven Gygi (HMS, Cell Biology), a world leader in proteomics, and Dr. Amy Lee (HMS, Cell Biology/Dana Farber Cancer Institute), an expert in transcription and RNA biology. Investigation of functional kleptoplasty in Sacoglossan sea slugs will fill a critical gap in our understanding of the evolution of endosymbiosis and the integration of novel organelles into host cells. Completion of these aims will reveal mechanisms used by slugs for sequestration and maintenance of chloroplasts, and thus advance our understanding of the origins and functions of organelles and the fundamental processes that drive the evolution of novel traits. These insights may have broad applications in biotechnology, and could serve as a blueprint to engineer other types of cells to perform photosynthesis, or to take up different foreign cargoes for applications in agriculture, medicine, or even space travel.