title: Evolutionary origins, molecular cloning and expression of carotenoid hydroxylases in eukaryotic photosynthetic algae.
abstract: BACKGROUND
  Xanthophylls, oxygenated derivatives of carotenes, play critical roles in photosynthetic apparatus of cyanobacteria, algae, and higher plants. Although the xanthophylls biosynthetic pathway of algae is largely unknown, it is of particular interest because they have a very complicated evolutionary history. Carotenoid hydroxylase (CHY) is an important protein that plays essential roles in xanthophylls biosynthesis. With the availability of 18 sequenced algal genomes, we performed a comprehensive comparative analysis of chy genes and explored their distribution, structure, evolution, origins, and expression.
  
  
  RESULTS
  Overall 60 putative chy genes were identified and classified into two major subfamilies (bch and cyp97) according to their domain structures. Genes in the bch subfamily were found in 10 green algae and 1 red alga, but absent in other algae. In the phylogenetic tree, bch genes of green algae and higher plants share a common ancestor and are of non-cyanobacterial origin, whereas that of red algae is of cyanobacteria. The homologs of cyp97a/c genes were widespread only in green algae, while cyp97b paralogs were seen in most of algae. Phylogenetic analysis on cyp97 genes supported the hypothesis that cyp97b is an ancient gene originated before the formation of extant algal groups. The cyp97a gene is more closely related to cyp97c in evolution than to cyp97b. The two cyp97 genes were isolated from the green alga Haematococcus pluvialis, and transcriptional expression profiles of chy genes were observed under high light stress of different wavelength.
  
  
  CONCLUSIONS
  Green algae received a β-xanthophylls biosynthetic pathway from host organisms. Although red algae inherited the pathway from cyanobacteria during primary endosymbiosis, it remains unclear in Chromalveolates. The α-xanthophylls biosynthetic pathway is a common feature in green algae and higher plants. The origination of cyp97a/c is most likely due to gene duplication before divergence of green algae and higher plants. Protein domain structures and expression analyses in green alga H. pluvialis indicate that various chy genes are in different manners response to light. The knowledge of evolution of chy genes in photosynthetic eukaryotes provided information of gene cloning and functional investigation of chy genes in algae in the future.
authors.affiliation: Key Laboratory of Coastal Biology and Biological Resources Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, People's Republic of China.
authors.forename: Hongli
authors.initials: H
authors.lastname: Cui
authors.forename: Xiaona
authors.initials: X
authors.lastname: Yu
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Yulin
authors.initials: Y
authors.lastname: Cui
authors.forename: Xueqin
authors.initials: X
authors.lastname: Li
authors.forename: Zhaopu
authors.initials: Z
authors.lastname: Liu
authors.forename: Song
authors.initials: S
authors.lastname: Qin
mesh_terms: D000595:Amino Acid Sequence; D000460:Chlorophyta / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects; D008027:Light / Q000009:adverse effects; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010788:Photosynthesis / Q000235:genetics* / Q000528:radiation effects; D017434:Protein Structure, Tertiary; D013312:Stress, Physiological / Q000235:genetics / Q000528:radiation effects; D024341:Xanthophylls / Q000096:biosynthesis / Q000378:metabolism*
chemical_list: D024341:Xanthophylls; D006899:Mixed Function Oxygenases