In 2008,a green tide broke out before the sailing competition of the 29th Olympic Games in Qingdao.The causative species was determined to be Enteromorpha prolifera (Ulva prolifera O.F.Müller),a familiar green macroalga along the coastline of China.Rapid accumulation of a large biomass of floating U.prolifera prompted research on different aspects of this species.In this study,we constructed a nonnormalized cDNA library from the thalli of U.prolifera and acquired 10 072 high-quality expressed sequence tags (ESTs).These ESTs were assembled into 3 519 nonredundant gene groups,including 1 446 clusters and 2 073 singletons.After annotation with the nr database,a large number of genes were found to be related with chloroplast and ribosomal protein,GO functional classification showed 1 418 ESTs participated in photosynthesis and 1 359 ESTs were responsible for the generation of precursor metabolites and energy.In addition,rather comprehensive carbon fixation pathways were found in U.prolifera using KEGG.Some stress-related and signal transduction-related genes were also found in this study.All the evidences displayed that U.prolifera had substance and energy foundation for the intense photosynthesis and the rapid proliferation.Phylogenetic analysis of cytochrome c oxidase subunit I revealed that this green-tide causative species is most closely affiliated to Pseudendoclonium akinetum (Ulvophyceae). In 2008, a green tide broke out before the sailing competition of the 29th Olympic Games in Qingdao. The causative species was determined to be Enteromorpha prolifera (Ulva prolifera OFMüller), a familiar green macroalga along the coastline of China. Rapid accumulation of a large biomass of floating U. prolifera prompted research on different aspects of this species. In this study, we constructed a non-normalized cDNA library from the thalli of U. prolifera and acquired 10 072 high-quality expressed sequence tags (ESTs). These ESTs were assembled into 3 519 nonredundant gene groups, including 1 446 clusters and 2 073 singletons. After annotation with the nr database, a large number of genes were found to be related with chloroplast and ribosomal protein, GO functional classification showed 1 418 ESTs participated in photosynthesis and 1 359 ESTs were responsible for the generation of precursor metabolites and energy.In addition, rather comprehensive carbon fixation pathways were found in U.prolife ra using KEGG. Home stress-related and signal transduction-related genes were also found in this study. All the evidences displayed that U. prolifera had substance and energy foundation for the intense photosynthesis and the rapid proliferation. Phylogenetic analysis of cytochrome c oxidase subunit I revealed that this green-tide causative species is most closely affiliated to Pseudendoclonium akinetum (Ulvophyceae).