Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Universidad Nacional de Rosario, Rosario, Argentina.
Program of Plant Metabolism and Metabolic Engineering, Centre for Research in Agricultural Genomics (CRAG) CSIC-IRTA-UAB-UB, Campus UAB Bellaterra, Barcelona, Spain.
J Exp Bot. 2018 Sep 14;69(20):4921-4933. doi: 10.1093/jxb/ery242.
Plastidial isoprenoids, such as carotenoids and tocopherols, are important anti-oxidant metabolites synthesized in plastids from precursors generated by the methylerythritol 4-phosphate (MEP) pathway. In this study, 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 resulted in slightly higher levels of γ-tocopherol. Plants deficient in the 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 and this was associated with increased DNA damage and decreased photosynthesis after exposure to UV-B. Genetic blockage of tocopherol biosynthesis did not affect DNA damage accumulation. In contrast, lut2 mutants that accumulate β,β-xanthophylls showed decreased DNA damage when irradiated with UV-B. Analysis of aba2 mutants showed that UV-B protection was not mediated by ABA (a hormone derived from β,β-xanthophylls). Plants accumulating β,β-xanthophylls also showed decreased oxidative damage and increased expression of DNA-repair enzymes, suggesting that this may be a mechanism for these plants to decrease DNA damage. In addition, in vitro experiments also provided 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 may also contribute to protection against UV-B.
质体类异戊二烯，如类胡萝卜素和生育酚，是质体中由甲基赤藓醇 4-磷酸（MEP）途径生成的前体合成的重要抗氧化代谢物。在这项研究中，我们发现，用 UV-B 照射拟南芥植物会强烈增加光保护叶黄素玉米黄质的积累，但也会导致γ-生育酚的水平略高。缺乏 MEP 酶 1-脱氧-D-木酮糖 5-磷酸合酶和 1-羟-2-甲基-2-丁烯基 4-二磷酸合酶的植物，类胡萝卜素和生育酚的含量普遍降低，这与暴露于 UV-B 后 DNA 损伤增加和光合作用下降有关。生育酚生物合成的遗传阻断不会影响 DNA 损伤的积累。相比之下，积累β，β-叶黄素的 lut2 突变体在受到 UV-B 照射时，DNA 损伤减少。对 aba2 突变体的分析表明，UV-B 保护不是由 ABA（一种来自β，β-叶黄素的激素）介导的。积累β，β-叶黄素的植物也表现出氧化损伤减少和 DNA 修复酶表达增加，表明这可能是这些植物减少 DNA 损伤的一种机制。此外，体外实验也提供了证据表明，β，β-叶黄素可以通过吸收辐射直接保护 DNA 免受损伤。总之，我们的结果表明，防止过度光照的叶黄素类胡萝卜素也可能有助于防止 UV-B。
