Meringosphaera as a new model to study the origin of plastids by endosymbiosis

Time period:

1 January 2026 – 31 December 2029

Project leader:

Fabien Burki

Project member:

Omaya Dudin, Filip Husnik

Funder:

Swedish Research Council

Type of award:

Project grant

Total funding:

4,435,000 SEK

Endosymbioses have profoundly shaped the diversity of life, with plastid evolution driving the rise of algae and land plants that sustain global biogeochemical cycles. However, the transition from free-living organisms to photosynthetic organelles remains poorly understood due to the ancient origins of plastids. In this proposal, we will investigate the endosymbiosis in Meringosphaera, a marine group of uncultured micro-organisms that may represent an ongoing plastid acquisition. Recently, we have started working on Meringosphaera populations from the Swedish West Coast, showing that it exhibits remarkable diversity within a heterotrophic clade while maintaining photosynthetic endosymbionts of eukaryotic algal origin. Preliminary data suggest genetic integration of these endosymbionts, indicating a potential step toward organellogenesis. To unravel this process, here we have assembled an international team with expertise in super-resolution microscopy, single-cell transcriptomics, and stable isotope probing. These advanced methods will be used to elucidate the cellular, genetic, and metabolic integration of Meringosphaera’s endosymbionts, which will provide critical insights into plastid evolution and the mechanisms driving organelle formation, and a path forward to study the vast majority of uncultured microbial eukaryotic diversity.