Evolutionary History of the Photolyase/Cryptochrome Superfamily in Eukaryotes.
BACKGROUND
Photolyases and cryptochromes are evolutionarily related flavoproteins, which however perform distinct physiological functions. Photolyases (PHR) are evolutionarily ancient enzymes. They are activated by light and repair DNA damage caused by UV radiation. Although cryptochromes share structural similarity with DNA photolyases, they lack DNA repair activity. Cryptochrome (CRY) is one of the key elements of the circadian system in animals. In plants, CRY acts as a blue light receptor to entrain circadian rhythms, and mediates a variety of light responses, such as the regulation of flowering and seedling growth.


RESULTS
We performed a comprehensive evolutionary analysis of the CRY/PHR superfamily. The superfamily consists of 7 major subfamilies: CPD class I and CPD class II photolyases, (6-4) photolyases, CRY-DASH, plant PHR2, plant CRY and animal CRY. Although the whole superfamily evolved primarily under strong purifying selection (average ω = 0.0168), some subfamilies did experience strong episodic positive selection during their evolution. Photolyases were lost in higher animals that suggests natural selection apparently became weaker in the late stage of evolutionary history. The evolutionary time estimates suggested that plant and animal CRYs evolved in the Neoproterozoic Era (~1000-541 Mya), which might be a result of adaptation to the major climate and global light regime changes occurred in that period of the Earth's geological history.
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, People's Republic of China.
Qiming
Q
Mei
School of Biological Sciences, the University of Hong Kong, Pokfulam Rd., Hong Kong SAR, People's Republic of China; Department of Life Sciences, College of Science and General Studies, Alfaisal University, Riyadh, Kingdom of Saudi Arabia.
Volodymyr
V
Dvornyk
D000818:Animals; D001105:Archaea / Q000145:classification / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism; D005075:Biological Evolution; D002940:Circadian Rhythm / Q000235:genetics*; D056931:Cryptochromes / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D005658:Fungi / Q000145:classification / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008027:Light; D010802:Phylogeny; D010944:Plants / Q000145:classification / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012641:Selection, Genetic
D056931:Cryptochromes; D004255:Deoxyribodipyrimidine Photo-Lyase