title: Light-promoted rhodopsin expression and starvation survival in the marine dinoflagellate Oxyrrhis marina.
abstract: The discovery of microbial rhodopsins in marine proteobacteria changed the dogma that photosynthesis is the only pathway to use the solar energy for biological utilization in the marine environment. Although homologs of these rhodopsins have been identified in dinoflagellates, the diversity of the encoding genes and their physiological roles remain unexplored. As an initial step toward addressing the gap, we conducted high-throughput transcriptome sequencing on Oxyrrhis marina to retrieve rhodopsin transcripts, rapid amplification of cDNA ends to isolate full-length cDNAs of dominant representatives, and quantitative reverse-transcription PCR to investigate their expression under varying conditions. Our phylogenetic analyses showed that O. marina contained both the proton-pumping type (PR) and sensory type (SR) rhodopsins, and the transcriptome data showed that the PR type dominated over the SR type. We compared rhodopsin gene expression for cultures kept under light: dark cycle and continuous darkness in a time course of 24 days without feeding. Although both types of rhodopsin were expressed under the two conditions, the expression levels of PR were much higher than SR, consistent with the transcriptomic data. Furthermore, relative to cultures kept in the dark, rhodopsin expression levels and cell survival rate were both higher in cultures grown in the light. This is the first report of light-dependent promotion of starvation survival and concomitant promotion of PR expression in a eukaryote. While direct evidence needs to come from functional test on rhodopsins in vitro or gene knockout/knockdown experiments, our results suggest that the proton-pumping rhodopsin might be responsible for the light-enhanced survival of O. marina, as previously demonstrated in bacteria.
authors.affiliation: Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340, United States of America; Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
authors.forename: Zhiling
authors.initials: Z
authors.lastname: Guo
authors.affiliation: Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340, United States of America; Department of Environmental Science, Ocean University of China, Qingdao, Shandong 266100, China.
authors.forename: Huan
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Marine Sciences, University of Connecticut, Groton, Connecticut 06340, United States of America; State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian 361005, China.
authors.forename: Senjie
authors.initials: S
authors.lastname: Lin
mesh_terms: D000595:Amino Acid Sequence; D004141:Dinoflagellida / Q000737:chemistry / Q000166:cytology* / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation; D008027:Light; D008969:Molecular Sequence Data; D010802:Phylogeny; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics*; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics*; D013217:Starvation; D059467:Transcriptome
chemical_list: D015800:Protozoan Proteins; D012243:Rhodopsin