title: An ancient light-harvesting protein is critical for the regulation of algal photosynthesis.
abstract: Light is necessary for photosynthesis, but its absorption by pigment molecules such as chlorophyll can cause severe oxidative damage and result in cell death. The excess absorption of light energy by photosynthetic pigments has led to the evolution of protective mechanisms that operate on the timescale of seconds to minutes and involve feedback-regulated de-excitation of chlorophyll molecules in photosystem II (qE). Despite the significant contribution of eukaryotic algae to global primary production, little is known about their qE mechanism, in contrast to that in flowering plants. Here we show that a qE-deficient mutant of the unicellular green alga Chlamydomonas reinhardtii, npq4, lacks two of the three genes encoding LHCSR (formerly called LI818). This protein is an ancient member of the light-harvesting complex superfamily, and orthologues are found throughout photosynthetic eukaryote taxa, except in red algae and vascular plants. The qE capacity of Chlamydomonas is dependent on environmental conditions and is inducible by growth under high light conditions. We show that the fitness of the npq4 mutant in a shifting light environment is reduced compared to wild-type cells, demonstrating that LHCSR is required for survival in a dynamic light environment. Thus, these data indicate that plants and algae use different proteins to dissipate harmful excess light energy and protect the photosynthetic apparatus from damage.
authors: Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102, USA.
authors: Graham
authors: G
authors: Peers
authors: Thuy B
authors: TB
authors: Truong
authors: Elisabeth
authors: E
authors: Ostendorf
authors: Andreas
authors: A
authors: Busch
authors: Dafna
authors: D
authors: Elrad
authors: Arthur R
authors: AR
authors: Grossman
authors: Michael
authors: M
authors: Hippler
authors: Krishna K
authors: KK
authors: Niyogi
mesh_terms: D000064:Acclimatization / Q000528:radiation effects; D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival / Q000528:radiation effects; D016825:Chlamydomonas reinhardtii / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D005453:Fluorescence; D005816:Genetic Complementation Test; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010788:Photosynthesis / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: D020418:Algal Proteins; D045342:Light-Harvesting Protein Complexes; D012333:RNA, Messenger; D002734:Chlorophyll