A LOV-domain photoreceptor mediates phototaxis in brown algae

Loss of the LOV-domain protein Helmchrome (HELM) in the brown alga Ectocarpus abolishes phototactic accumulation and directional orientation while leaving basal motility and fertilization intact.

• Why it matters: Phototaxis is vital for survival, but the molecular basis of light-directed movement is still unclear in many stramenopiles, limiting understanding of how distinct photoreceptor systems evolved.
• What they did: Using functional genetics, cell biology, and evolutionary analyses, the study shows HELM localizes to the posterior flagellum and underlies flavin-associated fluorescence in brown algal gametes.
• The result: HELM-like proteins are found across diverse stramenopile lineages, and their domain architecture evolved via repeated duplication of an ancestral RGS-LOV module, defining a distinct phototaxis system.

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