Exploring Meiosis in Brown Algae: Meiotic Axis Proteins in the model brown alga Ectocarpus

Most extant eukaryotic systems share core meiosis-specific genes, suggesting meiosis evolved only once in the last eukaryotic common ancestor (LECA). These genes have been characterized as master regulators of meiotic recombination, ensuring genetically diverse lineages. However, our understanding is limited as eukaryotic organisms beyond the animal, plant, and yeast lineages remain poorly understood. Recently, core meiotic genes have been identified in the genome of the model brown alga Ectocarpus, but currently lack proper characterization. Here, we combine bioinformatic, structural, and biochemical approaches to characterise the axial element orthologs, meiotic Ectocarpus HORMA domain protein (ecHOP1) and its interactor, reductional division protein 1 (ecRED1), in order to elucidate the molecular mechanisms of synaptonemal complex (SC) and double strand break (DSB) formation in brown algae. We highlight novel domain architecture within ecHOP1 and ecRED1 that support HORMA domain conformational switches and quantify the thermodynamic parameters of these interactions. Together, our data suggests that brown algae may employ alternative HORMA domain regulation mechanisms compared with animal, plant and yeast systems, and provide clues for future studies on the evolutionary constraints and adaptation of meiosis across the tree of life.