title: Roles of xanthophyll carotenoids in protection against photoinhibition and oxidative stress in the cyanobacterium Synechococcus sp. strain PCC 7002.
abstract: Synechococcus sp. strain PCC 7002 is a robust, genetically tractable cyanobacterium that produces six different xanthophyll carotenoids (zeaxanthin, cryptoxanthin, myxoxanthophyll (myxol-2'-fucoside), echinenone, 3'-hydroxyechinenone, and synechoxanthin) and tolerates many environmental stresses, including high light intensities. Targeted mutations were introduced to block the branches of the carotenoid biosynthetic pathway leading to specific xanthophylls, and a mutant lacking all xanthophylls was constructed. Some of the mutants showed severe growth defects at high light intensities, and multi-locus mutants had somewhat lower chlorophyll contents and lower photosystem I levels. The results suggested that xanthophylls, particularly zeaxanthin and echinenone, might play regulatory roles in thylakoid biogenesis. Measurements of reactive oxygen (ROS) and nitrogen (RNS) species in the mutants showed that all xanthophylls participate in preventing ROS/RNS accumulation and that a mutant lacking all xanthophylls accumulated very high levels of ROS/RNS. Results from transcription profiling showed that mRNA levels for most genes encoding the enzymes of carotenogenesis are significantly more abundant after exposure to high light. These studies indicated that all xanthophylls contribute to protection against photo-oxidative stress.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Yuehui
authors.initials: Y
authors.lastname: Zhu
authors.forename: Joel E
authors.initials: JE
authors.lastname: Graham
authors.forename: Marcus
authors.initials: M
authors.lastname: Ludwig
authors.forename: Wei
authors.initials: W
authors.lastname: Xiong
authors.forename: Richard M
authors.initials: RM
authors.lastname: Alvey
authors.forename: Gaozhong
authors.initials: G
authors.lastname: Shen
authors.forename: Donald A
authors.initials: DA
authors.lastname: Bryant
mesh_terms: D049109:Cell Proliferation / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D020869:Gene Expression Profiling; D008027:Light; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009154:Mutation; D018384:Oxidative Stress / Q000528:radiation effects*; D010105:Oxygenases / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D026361:Reactive Nitrogen Species / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D046940:Synechococcus / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D013696:Temperature; D024341:Xanthophylls / Q000096:biosynthesis / Q000172:deficiency / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D024341:Xanthophylls; D006899:Mixed Function Oxygenases; D010105:Oxygenases; C093259:beta-carotene ketolase; C079232:beta-carotene hydroxylase