Construction and characterization of a normalized cDNA library of Nannochloropsis oculata (Eustigmatophyceae)

Abstract

We constructed and characterized a normalized cDNA library of Nannochloropsis oculata CS-179, and obtained 905 nonredundant sequences (NRSs) ranging from 431–1 756 bp in length. Among them, 496 were very similar to nonredundant ones in the GenBank (E ≤1.0e-05), and 349 ESTs had significant hits with the clusters of eukaryotic orthologous groups (KOG). Bases G and/or C at the third position of codons of 14 amino acid residues suggested a strong bias in the conserved domain of 362 NRSs (>60%). We also identified the unigenes encoding phosphorus and nitrogen transporters, suggesting that N. oculata could efficiently transport and metabolize phosphorus and nitrogen, and recognized the unigenes that involved in biosynthesis and storage of both fatty acids and polyunsaturated fatty acids (PUFAs), which will facilitate the demonstration of eicosapentaenoic acid (EPA) biosynthesis pathway of N. oculata. In comparison with the original cDNA library, the normalized library significantly increased the efficiencies of random sequencing and rarely expressed genes discovering, and decreased the frequency of abundant gene sequences.