Mapping of a cellular and molecular atlas reveals the basis of chytrid development. Jel800 Cell Cycle Transcriptome

The chytrids (phylum Chytridiomycota) are a major early-diverging fungal lineage of evolutionary and ecological 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 a holistic ‘atlas’ of the cellular and molecular basis of the chytrid life cycle, using the model species Rhizoclosmatium globosum. From our developmental atlas, we show that zoospores exhibit a niche biological repertoire dominated by ribosome aggregates and that encystment is associated with a transition from neutral glycolipids to polar lipids. We further 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 body, and show that intrasporangial zoospore development is governed by amoeboid cell morphologies resulting from endocytotic cargo transport from the interstitial maternal cytoplasm. Taken together, our results reveal hidden insights into chytrid developmental biology and provide an integrated platform for future investigations into early-diverging fungal cell biology.