Diatoms, siliceous micro-algae, are among the world's most prolific primary producers, contributing about one-fifth of global oxygen production. They are characterised by a tremendous biodiversity and an almost ubiquitous presence in the biosphere, with habitats in freshwater, marine and wet terrestrial environments. Consequently, multiple lifestyles and survival strategies have evolved to fit a wide variety of light climates, temperature ranges, and ecological niches.
They are considered one of the most diverse groups of eukaryotes and are the most diverse group of micro-algae, with an estimated number of 100,000 to 200,000 species. Sexual reproduction is the main driver of speciation, but in diatoms it is also the main mechanism for restoring cell size. As a result of their characteristic silica cell wall, repeated mitotic divisions cause a gradual decrease in the cell size of diatom populations, resulting in cell death. However, sexual reproduction can be initiated below a species-specific size threshold. Gametes are produced and fuse into a zygote, which expands into an auxospore, a large cell unique to diatoms, which eventually releases a large initial cell, restoring the original cell size. Although well described, the molecular drivers of this characteristic sequence of sexual cell stages are almost completely unexplored.
In this thesis, we performed physiological experiments in combination with genomics, transcriptomics and genome editing to investigate the genetic basis of life cycle regulation in the pennate diatom Cylindrotheca closterium, which we introduce here as a new model
