title: Suppression subtractive hybridization reveals transcript profiling of Chlorella under heterotrophy to photoautotrophy transition.
abstract: BACKGROUND
  Microalgae have been extensively investigated and exploited because of their competitive nutritive bioproducts and biofuel production ability. Chlorella are green algae that can grow well heterotrophically and photoautotrophically. Previous studies proved that shifting from heterotrophy to photoautotrophy in light-induced environments causes photooxidative damage as well as distinct physiologic features that lead to dynamic changes in Chlorella intracellular components, which have great potential in algal health food and biofuel production. However, the molecular mechanisms underlying the trophic transition remain unclear.
  
  
  RESULTS
  In this study, suppression subtractive hybridization strategy was employed to screen and characterize genes that are differentially expressed in response to the light-induced shift from heterotrophy to photoautotrophy. Expressed sequence tags (ESTs) were obtained from 770 and 803 randomly selected clones among the forward and reverse libraries, respectively. Sequence analysis identified 544 unique genes in the two libraries. The functional annotation of the assembled unigenes demonstrated that 164 (63.1%) from the forward library and 62 (21.8%) from the reverse showed significant similarities with the sequences in the NCBI non-redundant database. The time-course expression patterns of 38 selected differentially expressed genes further confirmed their responsiveness to a diverse trophic status. The majority of the genes enriched in the subtracted libraries were associated with energy metabolism, amino acid metabolism, protein synthesis, carbohydrate metabolism, and stress defense.
  
  
  CONCLUSIONS
  The data presented here offer the first insights into the molecular foundation underlying the diverse microalgal trophic niche. In addition, the results can be used as a reference for unraveling candidate genes associated with the transition of Chlorella from heterotrophy to photoautotrophy, which holds great potential for further improving its lipid and nutrient production.
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, People's Republic of China.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Fan
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Cui
authors.forename: Jianke
authors.initials: J
authors.lastname: Huang
authors.forename: Weiliang
authors.initials: W
authors.lastname: Wang
authors.forename: Weibo
authors.initials: W
authors.lastname: Yin
authors.forename: Zanmin
authors.initials: Z
authors.lastname: Hu
authors.forename: Yuanguang
authors.initials: Y
authors.lastname: Li
mesh_terms: D020418:Algal Proteins / Q000235:genetics; D052818:Autotrophic Processes; D018533:Biomass; D002708:Chlorella / Q000235:genetics* / Q000378:metabolism*; D019295:Computational Biology / Q000379:methods; D020451:Contig Mapping / Q000379:methods; D018076:DNA, Complementary / Q000378:metabolism; D020224:Expressed Sequence Tags; D005502:Food; D015723:Gene Library; D005821:Genetic Techniques; D008055:Lipids / Q000737:chemistry; D058086:Microalgae / Q000502:physiology; D008957:Models, Genetic; D009693:Nucleic Acid Hybridization; D010777:Photochemistry / Q000379:methods; D016133:Polymerase Chain Reaction / Q000379:methods; D012313:RNA / Q000378:metabolism; D013997:Time Factors
chemical_list: D020418:Algal Proteins; D018076:DNA, Complementary; D008055:Lipids; D012313:RNA