Characterization of meiotic axis proteins in the model brown alga Ectocarpus.

Most eukaryotes share core meiosis-specific genes, suggesting meiosis evolved once in the last eukaryotic common ancestor (LECA). These genes are master regulators of meiotic recombination, ensuring genetically diverse lineages. However, meiosis in organisms outside the animal, plant, and yeast lineages remains poorly understood. Core meiotic genes were recently identified in the model brown alga Ectocarpus but remain uncharacterised. Here, we combine bioinformatic, structural, and biochemical approaches to characterise the axial-element orthologues meiotic Ectocarpus HORMA-domain protein (ecHOP1) and its interactor reductional division protein 1 (ecRED1), providing insight into meiotic-recombination regulation in brown algae. We define the chromatin-binding region of ecHOP1 and show that it binds double-stranded DNA, and we find that Ectocarpus assembles its axial element using evolutionarily conserved principles in a unique combination. Our work lays a foundation for further studies of meiosis in brown algae and broadens understanding of the diversity and conservation of meiotic mechanisms.