Comparison of the transcriptomes of the two species of whiteflies after reassembly
Whiteflies (Hemiptera: Aleyrodidae) are important agriculture pests that feed on a wide range of crops and transmit plant viruses. Species of the tobacco whitefly (Bemisia tabaci) complex distribute mostly in tropics and subtropics, while the greenhouse whitefly (Trialeurodes vaporariorum) in temperate regions. While both B. tabaci and T. vaporariorum have widespread distributions, they show apparent differences in many aspects of biology such as adaptability to host plants, tolerance to temperature, and resistance to insecticides. However the molecular basis underlying their differences remains largely unknown. In this study, we first reassembled the raw sequencing reads of a published transcriptome of the Mediterranean species of the B. tabaci complex using the Trinity method, and obtained an improved version of transcriptome with a total of 71,596 sequences (N50 = 726bp). Then, we analyzed the transcriptome divergences between the Mediterranean species and the greenhouse whitefly. We identified 2,944 pairs of high quality orthologous genes. The average divergence of the coding sequence between the two species of whiteflies was 18.1%, which is higher than that between human and rat (14.1%). The average nonsynonymous (Ka) and synonymous (Ks) substitution rates and the ratio of Ka/Ks of the orthologous genes were 0.0389, 2.23 and 0.0204 respectively. The average Ka/Ks ratio was much lower than that ratio between human and rat (0.170). These results indicate that these genes have evolved under highly selective constraints, and the two species are quite far related. We matched the orthologous genes to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and found that the most divergent gene classes are related to metabolism of ubiquinone, folate, and xenobiotics by cytochrome P450. These results suggest that the genes related to the metabolism of these substances might contribute to the divergence of the two species of whiteflies.
