Genomics and proteomics of nucleomorph-containing algae

The Archibald Laboratory uses molecular biological and computational methods to study the genes and genomes of eukaryotic (nucleus-containing) organisms. Our work focuses on the cryptophytes and chlorarachniophytes, two highly unusual groups of algae that acquired photosynthesis through a process called 'secondary endosymbiosis'. This occurs when a phagotrophic (cell-eating) eukaryote engulfs a photosynthetic eukaryote and retains its light-harvesting apparatus (plastid), and has given rise to some of the most ecologically significant phototrophs on the planet. In most secondary plastid-containing algae, (e.g., diatoms and kelp), the nucleus of the secondary endosymbiont has completely disappeared, having transferred all essential genes to the nuclear genome of the host cell. However, in cryptophytes and chlorarachniophytes, the endosymbiont nucleus persists in a miniaturized form called a 'nucleomorph', and the endosymbiont-derived cytoplasm (the 'periplasmic space') is retained as the site of essential cellular processes such as DNA replication, transcription and translation. As the coding capacity of nucleomorph genomes is extremely limited, most of the proteins functioning in the periplastid space must be host nucleus-encoded, but the diversity of cellular processes taking place in this unusual cellular compartment are currently unknown. Using a battery of molecular, biochemical and comparative genomic techniques, we will analyze the plastid, periplastid and nucleomorph proteomes of cryptophyte and chlorarachniophyte algae in order to (1) elucidate their true biochemical complexity and (2) understand the extent to which host- and endosymbiont-derived proteins have contributed to the molecular machines now functioning in both the host and endosymbiont cytoplasmic compartments. This research will provide insight into the minimal molecular machinery required to sustain core eukaryotic cellular processes and, more generally, shed light on an endosymbiotic process that has given rise to countless species of secondary plastid-containing algae on Earth.