Transcriptomic Analysis Of Guts From Two Invasive Whitefly Species

The whitefly Bemisa tabaci (Gennadius) (Hemiptera:Aleyrodidae) is a species complex including more than 35 cryptic species, some of which are the most destructive invasive pests of crops worldwide.Over the past 20 years, two species of the whitefly B. tabaci species complex, Middle East Asia Minor 1 (MEAM1) and Mediterranean (MED), have both spread from their origin, Middle East/Mediterranean, to many countries. The invasive ability and damage potential of MEAM1 has earned it a place as one of the world’s top 100 invasive species. The biological advantages of invasive whiteflies in host range, resistance to insecticides and secondary metabolite of plants and mating behavior are the crucial factors for them to replace indigenous species. While both MEAM1 and MED are destructive invasive species, their biological characteristics are quite different. For example, the invasion of MED seems more closely related to its strong resistance to major classes of insecticides, such as pyriproxyfen and neonicotinoids. Besides, the two species differ substantially in host range. Invasive species are valuable model systems for examining the evolutionary processes and molecular mechanisms associated with their specific characteristics by comparison with closely related species.The guts of phloem feeding insects are critical for nutrition uptake and xenobiotics degradation. Although the guts of whiteflies are also important, genomic information for them is limited. This might be partly due to the the fact that the body length of adult whiteflies is only 1 mm and the gut was much smaller, which makes the collection of micrograms of whitefly gut RNA difficult. To overcome this obstacle, the cDNA amplification method was utilized. The amplified gut cDNA was used for library construction and Illumina sequencing.Results are summarized as follows:(1) MEAM1 gut transcriptomeIn this study, the gut transcriptome of MEAM1 cryptic species of the B. tabaci complex was analyzed using the Illumina sequencing. A total of 12,879 MEAM1 unigenes were annotated with a significant BLAST hit.(2) Comparison of MEAM1 gut transcriptome and MEAM1 whole body transcriptomeTo unraval the functions of whitefly guts, we compared the transcriptomes of MEAM1 gut and whole body and finally, a total of 7,000 specificly expressed genes were identified in MEAM1 gut. Interestingly, those genes are annotated to the genes playing important roles in metabolism of insecticides and secondary plant chemicals.(3) Analysis between MEAM1 and MED gut transcriptomesTo explore the molecular differences between guts of MEAM1 and MED, comparisons between gut transcriptomes of the two species were conducted and 3,910 pairs of orthologous genes were identified. Based on the ratio of nonsynonymous and synonymous substitutions,15 sequences were found evolving under positive selections. Many of those genes are predicted to be involved in metabolism and insecticide resistance. Furthermore, the genes related to detoxification were found expressed at an elevated level in the gut of MED, which might be responsible for the whitefly’s higher resistance to insecticides and environmental stresses compared to MEAM1.Overall, the sequencing of MEAM1 gut transcriptomes and extensive comparisons of MEAM1 and MED gut genomica information provide substantial resource for an insight into roles of guts in whiteflies, and the mechanisms of MEAMI and MED whitefly invasion...