Global Analysis Of Transcriptional Differences Between Invasive And Closely Related Indigenous Whiteflies

The whitefly Bemisa tabaci is a complex composed of more than35cryptic species some of which are the most destructive invasive pests of crops worldwide. Due to their highly invasive and destructive characteristics, the two cryptic species MEAM1and MED have caused remarkable losses to crops worldwide. Great efforts have been made to investigate the mechanisms responsible for MEAM1and MED’s successful invasion and displacement of indigenous species, and major findings have been obtained on the following aspects:MEAM1has a wider range of host plants, higher capacity of insecticide resistance and greater environmental adaptive ability; moreover, asymmetric mating interactions between MEAM1and indigenous whiteflies are considered as a crucial mechanism leading to MEAM1’s successful invasion. As for MED, many studies indicate that this species has strong resistance to insecticides and can tolerate high temperature. There are also reports that MEAM1or MED and some viruses can form indirectly mutualistic relationship via plants. All of these may contribute to MEAM1and MED’s successful invasion and displacement of indigenous species. However, due to the lacking of genome data, we have little understanding about the molecular mechanisms underlying MEAM1and MED’s invasion. Our study constitutes two parts. In the first part, we compared the transcriptional differences between MEAM1, MED and Asia Ⅱ3and tried to find the molecular mechanisms related to MEAM1and MED’s invasion and displacement of Asia Ⅱ3; in the second part, we analyzed the changes of gene expression of MEAM1and Asia Ⅱ3before and after the transfer from cotton to tobacco and tried to find out why MEAM1is able to better adapt to tobacco than Asia Ⅱ3. Our results are summarized as follows:(1) Transcription analysis of MEAM1, MED and Asia Ⅱ3From our analysis, we found that2,422genes between MEAM1and MED,3,644genes between MEAM1and Asia Ⅱ3, and3,073genes between MED and Asia Ⅱ3were differentially expressed. Gene ontology enrichment analysis revealed that the differently expressed genes between the invasive and indigenous whiteflies were significantly enriched in the term of’oxidoreductase activity’. Pathway enrichment analysis showed that carbohydrates, amino acid and glycerolipid metabolisms were more active in MEAM1and MED than in Asia Ⅱ3, which may contributes to their differences in biological characteristics. Our analysis also illustrated that the majority of genes involved in‘drug metabolic pathway’were expressed at a higher level in MEAM1and MED than in Asia Ⅱ3. Taken together, these results revealed that compared to those of the indigenous species, the genes related to basic metabolism and detoxification were expressed at an elevated level in the invasive whiteflies, which might be responsible for their higher resistance to insecticides and environmental stresses.(2) Transcriptional variation of MEAM1and Asia Ⅱ3before and after transfer from cotton to tobaccoOn cotton plants, most detoxification, antioxidant and stress response genes were expressed at a higher level in MEAM1than in Asia Ⅱ3, indicating that MEAM1has a stronger intrinsic ability to cope with stress environment than Asia Ⅱ3. After transfer from cotton to tobacco plants for24h, more changes in gene expression were found in Asia Ⅱ3than in MEAM1. KEGG analysis showed that most genes involved in energy-generating, metabolism and ribosome were repressed. In comparison, MEAM1showed less responses to tobacco. Only protein turnover related pathways were enriched. We also found that P450, UGTs, GST genes were expressed at a higher level in MEAM1than in Asia Ⅱ3after feeding on cotton24h. Taken together, our findings indicate that MEAM1may have a higher ability to deal with unfavorable environment. So after transfer to tobacco, MEAM1was less affected while Asia Ⅱ3’s metabolism processes were greatly perturbed. This difference between the two species might be an important factor related to MEAM1’s invasion and displacement of indigenous species. Moreover, after transfer to tobacco, genes related to detoxification and antioxidant such as P450, UGTs, GST were expressed at a higher level in MEAM1than in Asia Ⅱ3, and this difference might be another reason contributing to MEAM1’s successful invasion and displacement of Asia Ⅱ3.In summary, we used transcription method to investigate the molecular mechanisms related to invasion by MEAM1and MED, and our findings have provided a new prospective for understanding the mechanisms underlying invasion.