After comparison with fold change threshold value and FDR test, there were 4,027 genes from the total 70,915 genes (5.68% of the genes) with a significant difference (P < 0.05) between PP and SP stages, including 2,220 upregulated genes and 1,807 downregulated genes. The distribution of the significant changes of 70,915 unigenes was illustrated in a scatter diagram (Figure 2), where the statistical significance of each unigene was plotted against fold change. Functional distribution of these DEGs was further analyzed by GO and KEGG enrichment, respectively.