Functional annotation of an expressed sequence tag library from Haliotis diversicolor and analysis of its plant-like sequences

The small abalone, Haliotis diversicolor, is a widely distributed and cultured species in the subtropical coastal area of China. To identify and classify functional genes of this important species, a normalized expressed sequence tag (EST) library, including 7069 high quality ESTs from the total body of H. diversicolor, was analyzed. A total of 4781 unigenes were assembled and 2991 novel abalone genes were identified. The GC content, codon and amino acid usage of the transcriptome were analyzed. For the accurate annotation of the abalone library, different influencing factors were evaluated. The gene ontology (GO) database provided a higher annotation rate (69.6%), and sequences longer than 800 bp were easily subjected to a BLAST search. The taxonomy of the BLAST results showed that lancelet and invertebrates are most closely related to abalone. Sixty-seven identified plant-like genes were further examined by reverse transcription–polymerase chain reaction (RT–PCR) and sequencing, only seven of these were real transcripts in abalone. Phylogenic trees were also constructed to illustrate the positions of two Cystatin sequences and one Calmodulin protein sequence identified in abalone. To perform functional classification, three different databases (GO, KEGG and COG) were used and 60 immune or disease-related unigenes were determined. This work has greatly enlarged the known gene pool of H. diversicolor and will have important implications for future molecular and genetic analyses in this organism.

Research highlights
► We reported the biggest dataset of small abalone in this paper to date, and has added nearly 3000 brand new genes to abalone gene pool.
► We also have done some works in plant-like gene survey, and reported 3 plant-like genes in abalone species for the first time.