Multi-omics approach identifies candidate phototaxis regulators in brown algae and reveals a novel kinase localized...

Phototaxis in brown algal gametes is a key behavioral response that enables successful fertilization and dispersal, yet the molecular basis underlying this process remains largely unexplored. Here, we applied an integrative multi-omics framework to identify candidate genes potentially involved in phototaxis. The framework revealed 20 orthogroups uniquely conserved in phototactic species but absent from non-phototactic lineages. Among these, only two orthogroups were previously characterized flagellar proteins: the blue-light photoreceptor Helmchrome, localized to the posterior flagellum, and the calcium-binding protein CABAF1, enriched in the anterior flagellum, indicating that these candidate genes may include previously unrecognized flagellar proteins functionally associated with Helmchrome and potentially involved in phototaxis. We further examined an ABC1-like kinase that emerged as a strong phototaxis-associated candidate and found that it localized to the electron-dense region of the paraflagellar body (PFB) in the posterior flagellum. This represents the first molecular component identified only at the PFB, a structure long recognized but lacking molecular characterization. Our findings provide a systematic framework for exploring the molecular mechanism of phototaxis in brown algae.