[Seminar] "Single-cell genomics and fluorescence microscopy indicate permanent plastid in a marine centrohelid" by Prof. Fabien Burki

Speaker: Prof. Fabien Burki, Senior Lecturer/Associate Professor at Department of Organismal Biology; Systematic Biology at Uppsala University [website]

Title: Single-cell genomics and fluorescence microscopy indicate permanent plastid in a marine centrohelid

Abstract:

Plastids have a complex evolutionary history. Though initially established through primary endosymbiosis between an ancient eukaryote and a cyanobacterium, plastids have since spread throughout the tree of eukaryotes not only vertically, but also horizontally. Several secondary and higher order endosymbioses have resulted in countless algae, which play crucial roles as primary producers in all environments. Yet, despite its evolutionary and ecological significance, the process that leads to the establishment of these endosymbiotically derived organelles is still poorly understood, in part due to the ancient origin of most plastids. We present Meringosphaera, a widespread marine centrohelid amoeba with the potential to shed light on this transition. Centrohelids have no history of photoautotrophy, but we previously showed that Meringosphaera contains at least two groups hosting distinct plastid-like organelles of Dictyochophyceae origin. Using single-cell genomics on geographically diverse environmental samples, here we reveal new key microdiversity and fully mirroring host and plastid phylogenomic trees, suggesting co-evolution and vertical transmission. We also find genetic evidence of plastid integration into the host genomes of the photosynthetic clades. Furthermore, using extensive double CARD-FISH screening, we show that Meringosphaera’s plastid are only found inside Meringosphaera cells, not in putative preys. Together, these results suggest that Meringosphaera does not steal its plastids, but instead represents an entirely new algal lineage in centrohelids. Meringosphaera is thus a unique system to study a more recent plastid integration.