Transcriptomic Analyses Reveal The Biological Roles Of Salivary Glands, Alimentary Canal And Bacteriocvtes In Mediterranean Cryptic Species Of Bemisia Tabaci Complex

The whitefly Bemisia tabaci (Gennadius)(Hemiptera:Aleyrodidae) is a species complex composed of more than36diverse cryptic species. Some cryptic species of the complex are remarkable destructive pests, which cause great damages to crops by excessive sap consumption and plant virus transmission. During the last20years, the Mediterranean (MED) species of the B. tabaci species complex has spread in many countries from their origin, and even replaced another invasive species, Middle East-Asia Minor1(MEAM1). According to previous studies, the successful invasion of MED whitefly is due to its biological advantages in host adaptability and resistance to insecticides.In order to unravel the mechanism underlying whitefly adaptation to plants and pesticides, the transcriptomes of the whitefly organs closely related to nutritional physiology were studied in a physiological and molecular view and the results were shown as followed.(1) Molecular characteristics of whitefly primary salivary glands and potential secretory proteins in the salivary glandsThrough transcriptome sequencing and SOAPdenovo assembly,13,615Unigenes were generated from whitefly primary salivary glands. Compared to the whole body transcriptome, the genes from whitefly primary salivary glands were enriched in the pathways and gene ontologies related to secretion and protein processing. The expression of565genes was upregulated in primary salivary glands compared to that in whole body. Among those upregulated genes, only74were annotatable and15of them were predicted to be involved in secretion and secretory protein processing. These data suggested the whitefly primary salivary glands play a crucial role in salivary protein systhesis and saliva secretion. A total of269potential secretory proteins were predicted from the salivary gland transcriptome. The annotation of the proteins indicated that salivary proteins may regulate plant defense signaling and detoxify inactivate plant toxins. Among the potential whitefly secretory proteins, only17proteins share a similarity with aphid (potential) secretory proteins, suggesting that the salivary proteins of phloem feeding insects are likely to be highly species specific.(2) The molecular characteristics of whitefly alimentary canalIn total,27,443Unigenes were generated from whitefly alimentary canal transcriptome. These genes were found to be significantly enriched in "xenobiotics biodegradation and metabolism","metabolism of cofactors and vitamins" and "digestive process" pathways. Compared to the whole body,5,771genes were specifically expressed in the alimentary canal. These genes were also enriched in "xenobiotics biodegradation and metabolism" and "digestive process". To reveal the possible roles of alimentary canal genes in the differences between MED and MEAM1, the amino acids similarity of the orthologous genes from those two specifies were analyzed. The results suggest that the detoxification relevant pathways and enzymes were under constraint selection and their divergence likely has an impact on different adaptive capability of whitefly.(3) Analysis of whitefly bacteriocytes transcriptomeIn whitefly bacteriocytes,5,010genes were predicted to be expressed by host. Functional analysis showed that the bacteriocyte genes were mainly enriched in metabolism relevant genes and "response to stimulus"genes. Compared to the whole body transcriptome, bacteriocytes upregulated genes were enriched in the pathways and gene ontologies related to amino acid metabolism and transport, as well as response to stimulus. It suggests that those host expressed genes have roles in not only providing symbionts with stable habitats and the needs for survival and reproduction but also controlling the growth and distribution of symbionts. According to the genomic sequence information of whitefly symbionts and bactericoytes, the whitefly was supposed to be able to obtain the essential amino acids (apart from arginine and histidine) from bacteriocytes to compensate the nutritional imbalance of phloem sap.Overall, the salivary glands, alimentary canal and bacterocytes are important in whitefly feeding, responding to plant defense and compasating the nutrition defect of phloem sap. These results unravel important features about whitefly-plant and whitefly-symbiont interactions and also, provide a rich source of target genes for developing novel pest control strategies.