To explore whether selection pressure had affected NnTPS genes, we calculated ratio (ω) of the synonymous substitution rate (dS) vs. the non-synonymous substitution rate (dN) using the program codeml from PAML (version 4). Generally, dN/dS ratio >1 indicates positive selection, a ratio < 1 indicates negative or purifying selection and a ratio = 1 indicates neutral evolution (Wang et al., 2005; Song et al., 2015). Results in Figure 5 showed that dN/dS ratios were always less than 1 for different domains and regions outside domain, suggesting purifying selection on lotus TPS gene family. The dN/dS ratios outside NnTPS domain were found to be much higher than the ratios inside the NnTPS domains (Figure 4). These results showed that NnTPS domains evolved faster than regions outside TPS domain. The relaxed purifying or positive selection in the regions outside TPS domain may lead to the above results.