A role for β,β-xanthophylls in Arabidopsis UV-B photoprotection.

Plastidial isoprenoids, such as carotenoids and tocopherols, are relevant anti-oxidant metabolites synthesized in plastids from precursors generated by the methylerythritol 4-phosphate (MEP) pathway. In this work, we found that irradiation of Arabidopsis thaliana plants with UV-B caused a strong increase in the accumulation of the photoprotective xanthophyll zeaxanthin but also slightly higher levels of γ-tocopherol. Plants deficient in MEP enzymes 1-deoxy-D-xylulose 5-phosphate synthase and 1-hydroxy-2-methyl-2-butenyl 4-diphosphate synthase showed a general reduction in both carotenoids and tocopherols associated with increased DNA damage and decreased photosynthesis after UV-B exposure. Genetic blockage of tocopherol biosynthesis did not affect DNA damage accumulation. In contrast, lut2 mutants accumulating β,β-xanthophylls showed decreased DNA damage when irradiated with UV-B. Analysis of aba2 mutants showed that UV-B protection is not mediated by ABA (a hormone derived from β,β-xanthophylls). Plants accumulating β,β-xanthophylls also show decreased oxidative damage and increased expression of DNA repair enzymes, suggesting that this can be a mechanism for these plants to decrease DNA damage. In addition, in vitro experiments also provide evidence that β,β-xanthophylls can directly protect against DNA damage by absorbing radiation. Together, our results suggest that xanthophyll cycle carotenoids that protect against excess illumination could also contribute to the protection against UV-B.