As an international standardized gene functional classification system, GO describes properties of genes and their products in many organisms and provides a comprehensive description of gene properties across species and databases (Hao et al. 2011). Based on the BlastX results, a total of 50,161 (29.00 %) unigenes were assigned into 49 GO term annotations, including three categories, i.e., molecular function, biological process, and cellular component (Fig. 3). Within the molecular function category (70,280 GO terms), “binding” (32,021, 45.6 %) and “catalytic activity” (26,742, 38.0 %) were the most highly represented terms. For biological process (108,214 GO terms), “cellular process” (28,941, 26.7 %) and “metabolic process” (29,813, 27.6 %) were the highly represented terms. Among the cellular component category (87,253 GO terms), “cell” (28,076, 32.2 %), “cell part” (13,723, 15.7 %) and “organelle” (28,076, 32.2 %) were the three main categories.Fig. 3GO classification of all annotated unigenes. GO classification of all annotated 50,161 unigenes. All terms belonged to the three main GO categories: biological process, cellular component and molecular function. The x-axis indicated the subcategories, the right y-axis indicated the number of genes in each category, the left y-axis indicated the percentage of a specific category of genes in the corresponding GO category. Red column indicated all annotated unigenes