Both major xanthophyll cycles present in nature can provide Non-Photochemical Quenching in the model diatomPhaeodactylum tricornutum

Xanthophyll cycling contributes to photoprotection by regulating Non-Photochemical Quenching (NPQ). While most photosynthetic eukaryotes including land plants use the violaxanthin cycle, some algae like diatoms and haptophytes rely on the diadinoxanthin cycle for photoprotection. These algae also contain minor amounts of violaxanthin cycle pigments, serving as precursors in xanthophylls biosynthesis. Both cycles are catalyzed by the enzymes violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). Here, we characterized the role of VDE and different ZEP-encoding paralogs ( ZEP2 and ZEP3 ) in the model diatom Phaeodactylum tricornutum . While knockout of VDE and ZEP3 significantly impaired the diadinoxanthin cycle, lack of ZEP2 led to sustained accumulation of the violaxanthin cycle instead of diadinoxanthin cycle pigments under high irradiance, with no negative effect on NPQ capacity. We demonstrate that both major xanthophyll cycles present in nature can function with comparable efficiency within the same species, offering a new perspective on the evolution of xanthophyll-mediated photoprotection.