Multi-modal single-cell profiling reveals transcriptional states and commitment dynamics during sexual reproduction in the diatom Pseudo-nitzschia multistriata

Diatoms, single-celled photosynthetic eukaryotes, traditionally considered primarily influenced by resource availability, are now recognized to exhibit complex developmental processes reminiscent of those in multicellular organisms. Sexual reproduction is an obligate choice in many species, albeit with variable frequency and efficiency. In order to explore decision making mechanisms and cellular heterogeneity inherent to this specific phase of the diatom life cycle, we applied a multi-modal strategy to follow sexual reproduction events in the model diatom Pseudo-nitzschia multistriata: i) we employed image-enabled cell sorting to link sexual stages morphology with gene expression ii) we developed a single-nucleus RNA sequencing assay, and iii) conducted proteomic profiling. Combining phenotypes with single-cell profiling allowed us to identify sexual state-specific transcription programs and different states within morphologically identical parental cells, revealing a widespread commitment of the majority of the population to sexual reproduction. This implies that the bottleneck to successful sexual reproduction in this species can be placed downstream of the signalling phase between mating cells, with additional, yet unidentified, factors influencing mating success at sea.