Diversification of DIX domain-containing proteins in the SAR supergroup.

Polarity establishment is crucial for development, cellular organization, and signaling in living organisms. In animals and plants, this process involves DIX domain-containing proteins (DDPs) that assemble into oligomers via head-to-tail DIX polymerization, facilitating localized protein aggregation. This study uncovers the unexpected diversity of DDPs within the SAR supergroup, characterizing four DDPs with novel domain combinations conserved in Stramenopiles and Alveolates. These proteins are predominantly found in micro-swimmers and species with a motile stage in their life cycle. We hypothesize that DDPs from these eukaryotic lineages may be involved in cell polarity-related processes, including those associated with motility. Our work provides insights for further investigations of DDPs in protists and will enable the development of evolution-informed control strategies against pathogens and parasites within this clade.