A cellular and molecular atlas reveals the basis of chytrid development.
The chytrids (phylum Chytridiomycota) are a major early-diverging fungal lineage of ecological and evolutionary importance. Despite their importance, many fundamental aspects of chytrid developmental and cell biology remain poorly understood. To address these knowledge gaps, we combined quantitative volume electron microscopy and comparative transcriptome profiling to create an atlas of the cellular and molecular basis of the chytrid life cycle, using the model chytrid Rhizoclosmatium globosum. From our developmental atlas, we show that zoospores exhibit a specialised biological repertoire dominated by inactive ribosome aggregates, and that lipid processing is complex and dynamic throughout the cell cycle. We demonstrate that the chytrid apophysis is a distinct subcellular structure characterised by high intracellular trafficking, providing evidence for division of labour in the chytrid cell plan, and show that zoosporogenesis includes animal like amoeboid cell morphologies resulting from endocytotic cargo transport from the interstitial maternal cytoplasm. Taken together, our results reveal insights into chytrid developmental biology and provide a basis for future investigations into early-diverging fungal cell biology.