Primary Salivary Glands Research Articles

The essential role of clathrin-mediated endocytosis and early endosomes in the trafficking of begomoviruses through the primary salivary glands of their whitefly vectors.

Many plant viruses are transmitted by insect vectors in a circulative manner. For efficient transmission, the entry of the virus from vector hemolymph into the primary salivary gland (PSG) is a step of paramount importance. Yet, vector components mediating virus entry into PSG remain barely characterized. Here, we demonstrate the role of clathrin-mediated endocytosis and early endosomes in begomovirus entry into whitefly PSG. Our findings unravel the key components involved in begomovirus transport within the whitefly body and transmission by their whitefly vectors and provide novel clues for blocking begomovirus transmission.

A novel salivary effector, BtE3, is essential for whitefly performance on host plants.

The whitefly Bemisia tabaci is a piercing-sucking herbivore that reduces the yields of crops both by feeding on plants and transmitting plant viruses. Like most plant feeders, B. tabaci has evolved ways to avoid plant defence responses. For example, B. tabaci is known to secrete salivary effectors to suppress host defences. However, the nature of B. tabaci effectors is not completely understood. In this study, we used B. tabaci genomic and salivary gland transcriptomic data and an overexpression system to identify a previously unknown B. tabaci salivary effector, BtE3. BtE3 is specifically expressed in the head (containing primary salivary glands) and is secreted into hosts during B. tabaci feeding. In planta overexpression of BtE3 blocked Burkholderia glumae-induced hypersensitive response (HR) in both Nicotiana benthamiana and Solanum lycopersicum. Silencing of BtE3 by plant-mediated RNAi prevented B. tabaci from continuously ingesting phloem sap, and reduced B. tabaci survival and fecundity. Moreover, overexpression of BtE3 in planta up-regulated the salicylic acid- (SA-) signalling pathway, but suppressed the downstream jasmonic acid- (JA-) mediated defences. Taken together, these results indicate that BtE3 is a B. tabaci-specific novel effector involved in B. tabaci-plant interactions. These findings increase our understanding of B. tabaci effectors and suggest novel strategies for B. tabaci pest management.

Clinicopathological and survival profile of patients with salivary gland myoepithelial carcinoma: A systematic review.

In this systematic review, we aimed to evaluate the clinicopathological and prognosis data of patients with myoepithelial carcinoma (MC) of the salivary glands. MEDLINE/PubMed, Scopus, and Embase search was performed with the keywords "myoepithelial carcinoma", "malignant myoepithelioma", and "salivary glands". Only primary salivary glands MC that fulfilled the World Health Organization diagnostic criteria were included. The Joanna Briggs Institute tool was used to assess the risk of bias. Forty-three studies (comprising data from 71 cases) met the inclusion criteria. The patients having MC showed a mean age of 56.4 ± 19.6 years with no sex predilection. The parotid was the most affected gland (49.3%) (49.3%). Clinically, the MC presented as an asymptomatic (65.1%) mass (84%). The most common histological findings were the presence of clear tumor cells (39.7%) and multinodular growth patterns (60.7%). Multivariate analysis showed plasmacytoid cell type (p=0.010) and solid growth pattern (p=0.003) were related to decreased disease-free survival (DFS). Surgery alone was the most used treatment (53.5%). Patients with a combination of treatments (surgery, radiation therapy with/without chemotherapy) showed a longer DFS (p=0.049). The 2-year and 5-year overall survival rates were 67.5% and 46.1% respectively. Salivary gland MC is a rare salivary cancer with no sex predilection, with a higher incidence in the parotid gland. Cell type, growth pattern, and treatment type may be related to a lower DFS. Overall, salivary gland MC presented low recurrence and metastasis rates.

LAMB3 and TACSTD2, both highly expressed in salivary gland mucoepidermoid carcinoma, represent potential diagnostic biomarkers and therapeutic targets

Salivary mucoepidermoid carcinoma (MEC) is the most common malignant tumor in major and minor salivary glands. The CRTC1-MAML2 or CRTC3-MAML2 gene arrangements, which occur in up to 80% of primary salivary glands with MEC, are the major oncogenic drivers of MEC carcinogenesis. However, the molecular consequences of these fusions remain unknown. We sought to identify the key functional genes involved in MEC, then characterize biomarkers with potential therapeutic relevance. We analyzed the gene expression profiles of two primary tumors (fusion-positive HCM-MEC020T and fusion-negative HCM-MEC030T); we compared them with the profiles of the established cell line HCM-MEC010 (derived from CRTC1-MAML2 fusion-positive MEC) and fibroblast cells derived from an HCM-MEC010 patient (non-tumor control cells). Fifty-three genes were identified as commonly expressed genes among the top 500 highly expressed genes in MEC but not in fibroblasts. Among these 53 genes, we focused on LAMB3 and TACSTD2, which are not predicted to be CRTC1/CRTC3-MAML2 target genes. LAMB3 (laminin subunit beta-3) is the basement membrane protein in normal salivary glands. TACSTD2 encodes a membrane protein associated with calcium signaling. To investigate the relationship between gene expression patterns and MEC pathological grade, we performed immunohistochemical staining of 13 MEC samples. LAMB3 and TACSTD2 proteins were expressed in the tumor cells of MEC samples (LAMB3, 12/13; TACSTD2, 13/13) but not in surrounding stromal cells. Although there were no statistically significant differences in LAMB3 or TACSTD2 expression among pathological grades, further studies are needed to elucidate the value of LAMB3 and TACSTD2 in clinical applications.

Homoeopathic Therapeutics in treatment of Ranula

Ranula is one of the rarest mucoceles that occurs on the mylohyoid muscle through the floor of the mouth present at the anterior two-thirds and typically comprise the primary salivary glands. Ranula arises ducts of the sublingual gland's Rivinus, which are located in the body of the sublingual gland, and exceptionally from the small salivary glands. This article deals with information about Ranula and its homoeopathic medicines that has great role in managing the swelling and terminating the Ranula and also helps in breaking the tendency of recurrences.

The Infection Route of Tomato Zonate Spot Virus in the Digestive System of Its Insect Vector Frankliniella occidentalis.

Tomato zonate spot virus (TZSV) is a phytopathogen of the genus Orthotospovirus (Bunyaviridae) that is widespread in many areas of Southwest China. TZSV is mainly transmitted by Frankliniella occidentalis, but its exact infection route remains unclear. To explore this issue, we detected the nucleocapsid protein of TZSV in the digestive systems of first-instar F. occidentalis nymphs fed with TZSV-infected pepper leaves. TZSV infection in the F. occidentalis digestive system begins within 4 h post-first access to diseased plants: The foregut is likely the primary site of infection, and primary salivary glands (PSGs) are the destination. There are three potential routes for TZSV transmission from the alimentary canal to the PSGs: (1) virus dissemination from the midgut to hemocoel followed by movement to the PSGs; (2) accumulation in midgut epithelial cells and arrival at PSGs via tubular salivary glands and efferent ducts; and (3) arrival at epitheliomuscular cells of the forepart of the midgut and movement along the ligament to the PSGs. We tested the transmission efficiency of F. occidentalis in second-instar nymphs and female and male adults. TZSV was transmitted in a persistent-propagative mode by both nymphs and adults, with adults appearing to show slightly higher transmission efficiency than nymphs. We confirmed the presence of all three routes for TZSV transmission in F. occidentalis and determined that like other Orthotospoviruses, TZSV is transmitted in a persistent-propagative manner. These results should facilitate the control of TZSV-related diseases and further our understanding of the transmission biology of Orthotospoviruses in general.

Differential Transmission of Old and New World Begomoviruses by Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) Cryptic Species of Bemisia tabaci.

Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) are two of the most invasive members of the sweetpotato whitefly, Bemisia tabaci, cryptic species complexes and are efficient vectors of begomoviruses. Bemisia tabaci MEAM1 is the predominant vector of begomoviruses in open-field vegetable crops in the southeastern United States. However, recently B. tabaci MED also has been detected in the landscape outside of greenhouses in Florida and Georgia. This study compared the transmission efficiency of one Old-World (OW) and two New-World (NW) begomoviruses prevalent in the southeastern United States, viz., tomato yellow leaf curl virus (TYLCV), cucurbit leaf crumple virus (CuLCrV), and sida golden mosaic virus (SiGMV) between B. tabaci MEAM1 and B. tabaci MED. Bemisia tabaci MEAM1 efficiently transmitted TYLCV, CuLCrV, or SiGMV, whereas B. tabaci MED only transmitted TYLCV. Percent acquisition and retention of OW TYLCV following a 72 h acquisition access period was significantly higher for B. tabaci MED than B. tabaci MEAM1. In contrast, B. tabaci MEAM1 acquired and retained significantly more NW bipartite begomoviruses, CuLCrV or SiGMV, than B. tabaci MED. Quantitative analysis (qPCR) of virus DNA in whitefly internal tissues revealed reduced accumulation of CuLCrV or SiGMV in B. tabaci MED than in B. tabaci MEAM1. Fluorescent in situ hybridization (FISH) showed localization of CuLCrV or SiGMV in the midgut of B. tabaci MED and B. tabaci MEAM1. However, localization of CuLCrV or SiGMV was only observed in the primary salivary glands of B. tabaci MEAM1 and not B. tabaci MED. TYLCV localization was observed in all internal tissues of B. tabaci MEAM1 and B. tabaci MED. Overall, results demonstrate that both B. tabaci MEAM1 and B. tabaci MED are efficient vectors of OW TYLCV. However, for the NW begomoviruses, CuLCrV and SiGMV, B. tabaci MEAM1 seems to a better vector.

A Retrospective Analysis of 235 Patients and 281 Radiotherapy Plans for Sialorrhea Treatment in Amyotrophic Lateral Sclerosis and Parkinson Patients

To evaluate the efficacy and safety of radiotherapy (RT) of the primary salivary glands in a large series of patients with amyotrophic lateral sclerosis (ALS) and Parkinson's disease with sialorrhea.Patients treated in our institution between 2010 and 2020 were retrospectively analyzed, including the first 50 patients prospectively analyzed. All patients included were refractory to conventional sialorrhea drug treatments. RT was delivered by a conventional LINAC, with 2 opposite beams including the two submandibular glands and two thirds of the two parotid glands before 2014, and from 2015 2 lateral beams including the submaxillary glands, and 2 opposite oblique beams directed to each parotid gland, with reduced oral cavity irradiation. The total dose delivered was 10 Gy in 2 fractions or 20 Gy in 4 fractions. RT efficacy was assessed using the 9-item Sialorrhea Scoring Scale (SSS), prospectively validated as the most effective and sensitive tool for measuring sialorrhea in ALS patients.A total of 235 patients were included, and 281 treatments (45 reirradiations, 1 patient received 3 irradiations). Median age was 69 years (range: 38 - 95), 127 women (54%) and 126 men (46%), 212 had ALS (90%), 17 had Parkinson's disease (7%), and 5 patients (3%) had another neurological disorder. Median interval between the first and second radiotherapy course was 7.5 months (range: 1 - 37). The median SSS score before radiation therapy was 8 (range: 6 - 9), and the median SSS score at 1 month of irradiation was 2 (range: 1 - 6). There was no toxicity of > grade 1. At the end of RT, all but one patient had an improvement in SSS score: 272 had a complete response (CR) (97%, SSS 1-3) and 8 had a partial response (PR) (3%, SSS 4-5); one patient had a stable SSS score (< 1%). A 1-month CR after RT was achieved in 96% of the 235 patients who underwent a primary RT, and 100% of the 45 patients who received re-irradiation. Patients treated with 20Gy versus 10Gy during the first RT treatment were more likely to have a CR at 1 month (99% vs. 91%, P = 0.007), and had a greater decrease in SSS score (mean difference -6 vs. -5 points, P < 0.001). Also, the 45 patients who received reirradiation were more frequently previously treated with the RT 10Gy protocol (25/45 patients, 55%) versus 60/191 (31%) in patients who did not require reirradiation (P < 0.001). The 3-beam irradiation technique, used from 2014 and beyond, did not significantly improve treatment efficacy (reduction of the SSS score by -5.8 points on average versus -5.6 points previously, P = 0.3). Nevertheless, it reduced 1 month toxicity, in particular decreased saliva thickening discomfort (P < 0.001).A 20 Gy irradiation in 4 fractions is an effective treatment for ALS patients with sialorrhea, with minimal toxicity, particularly by separately targeting parotid and submaxillary glands. A shorter RT (10 Gy in 2 fractions) may be proposed in patients with poor medical condition, subject to its lower efficacy and the greater need for reirradiation.

A review on salivary biomarkers in carcinoma diagnosis

Carcinoma is the 2nd leading mortality in the U.S. Signs &amp; symptoms include typically unspecific until the tumours metastasize. Hence, an urgency is there for quick, precise, and non-invasive carcinoma diagnosis, rapid detection, diagnosis, stage surveys, &amp; forecasts. Saliva is a multi-structural fluid, found in the oral region, containing secretions from primary and minor salivary glands. Species can even be found in blood-present molecules including Deoxyribo Nucleic Acids, RNAs, hormones, metabolites, and microbiota. Recently, saliva testing received considerable interest in identifying specific biomarkers as sample collection and processing is quick, cost-effective, accurate and doesn’t put any distress on the patient. We examine recent salivary biomarkers of systemic carcinoma by separating them into genomically, transcriptomically, proteomically, metabolomic and microbially dependent forms.

Transmission mode of watermelon silver mottle virus by Thrips palmi.

Thrips and thrips-transmitted tospoviruses cause significant losses in crop yields worldwide. The melon thrips (Thrips palmi) is not only a pest of cucurbit crops, but also a vector that transmits tospoviruses, such as the watermelon silver mottle virus (WSMoV). Vector transmission of tospoviruses has been well studied in the tomato spotted wilt virus (TSWV)-Frankliniella occidentalis model system; however, until now the transmission mode of WSMoV by T. palmi has not been sufficiently examined. The results of the transmission assays suggest that T. palmi transmits WSMoV in a persistent manner, and that the virus is mainly transmitted by adults, having been ingested at the first-instar larval stage. Complementary RNAs corresponding to the NSm and NSs genes of WSMoV were detected in viruliferous thrips by reverse transcription-polymerase chain reaction; NSs protein was also detected in viruliferous thrips by western blotting, verifying the replication of WSMoV in T. palmi. Furthermore, we demonstrated that in thrips infected with WSMoV at the first-instar larval stage, the virus eventually infected various tissues of the adult thrips, including the primary salivary glands. Taken together, these results suggest that T. palmi transmits WSMoV in a persistent-propagative mode. The results of this study make a significant contribution to the understanding of the transmission biology of tospoviruses in general.

Localization and Quantification of Begomoviruses in Whitefly Tissues by Immunofluorescence and Quantitative PCR.

Begomoviruses (genus Begomovirus, family Geminiviridae) are transmitted by whiteflies of the Bemisia tabaci complex in a persistent, circulative manner. Considering the extensive damage caused by begomoviruses to crop production worldwide, it is imperative to understand the interaction between begomoviruses and their whitefly vector. To do so, localization and quantification of the virus in the vector tissues is crucial. Here, using tomato yellow leaf curl virus (TYLCV) as an example, we describe a detailed protocol to localize begomoviruses in whitefly midguts, primary salivary glands, and ovaries by immunofluorescence. The method is based on the use of specific antibodies against a virus coat protein, dye-labeled secondary antibodies, and a confocal microscope. The protocol can also be used to colocalize begomoviral and whitefly proteins. We further describe a protocol for the quantification of TYLCV in whitefly midguts, primary salivary glands, hemolymph, and ovaries by quantitative PCR (qPCR). Using primers specifically designed for TYLCV, the protocols for quantification allow the comparison of the amount of TYLCV in different tissues of the whitefly. The described protocol is potentially useful for the quantification of begomoviruses in the body of a whitefly and a virus-infected plant. These protocols can be used to analyze the circulation pathway of begomoviruses in the whitefly or as a complement to other methods to study whitefly-begomovirus interactions.

Activation of the Stimulator of Interferon Gene Protein is Involved in the Etiopathogenesis of Sjogren’s Syndrome

Abstract Activation of innate immune responses and excessive production of type I Interferons (IFNs) plays a critical role in the pathogenesis of Sjögren’s syndrome (SS), a chronic autoimmune disorder affecting the exocrine salivary glands (SG). Recognition of nucleic acids by cytosolic nucleic acid sensors is a major trigger for type I IFN production. Several cytosolic DNA sensors interact downstream with the stimulator of interferon gene (STING) protein and induce type I IFNs. Although STING has been implicated in several interferonopathies, its role in SS is not known. To investigate whether STING activation is involved in the etiopathogenesis of SS, in this study, female C57BL/6 mice were injected with a STING agonist, dimethylxanthenone-4-acetic acid (DMXAA) and mice were followed for the development of SS. Systemic DMXAA treatment rapidly induced the expression of Ifnb1, Il6, and Tnfa in the SG, and these cytokines were also elevated in circulation. In contrast, increased Ifng gene expression was only detected in the SGs. The type I innate lymphoid cells present within the SG were the major source of IFNγ, and their numbers increased significantly within 3 days of DMXAA treatment. STING expression in SG was mainly observed in the ductal and interstitial cells. In primary SG cells, DMXAA activated STING, which caused phosphorylation of TBK1 and IRF3, and induced IFN-β production. The DMXAA-treated mice developed autoantibodies, sialoadenitis, and SG hypofunction. Our study demonstrates that activation of STING pathway holds the potential to initiate SS. Thus, apart from viral infections, conditions that cause cellular perturbations and accumulation of host DNA within the cytosol should also be considered as possible triggers for SS.

Activation of Stimulator of Interferon Genes (STING) and Sjögren Syndrome

Sjögren syndrome (SS), a chronic autoimmune disorder causing dry mouth, adversely affects the overall oral health in patients. Activation of innate immune responses and excessive production of type I interferons (IFNs) play a critical role in the pathogenesis of this disorder. Recognition of nucleic acids by cytosolic nucleic acid sensors is a major trigger for the induction of type I IFNs. Upon activation, cytosolic DNA sensors can interact with the stimulator of interferon genes (STING) protein, and activation of STING causes increased expression of type I IFNs. The role of STING activation in SS is not known. In this study, to investigate whether the cytosolic DNA sensing pathway influences SS development, female C57BL/6 mice were injected with a STING agonist, dimethylxanthenone-4-acetic acid (DMXAA). Salivary glands (SGs) were studied for gene expression and inflammatory cell infiltration. SG function was evaluated by measuring pilocarpine-induced salivation. Sera were analyzed for cytokines and autoantibodies. Primary SG cells were used to study the expression and activation of STING. Our data show that systemic DMXAA treatment rapidly induced the expression of Ifnb1, Il6, and Tnfa in the SGs, and these cytokines were also elevated in circulation. In contrast, increased Ifng gene expression was dominantly detected in the SGs. The type I innate lymphoid cells present within the SGs were the major source of IFN-γ, and their numbers increased significantly within 3 d of treatment. STING expression in SGs was mainly observed in ductal and interstitial cells. In primary SG cells, DMXAA activated STING and induced IFN-β production. The DMXAA-treated mice developed autoantibodies, sialoadenitis, and glandular hypofunction. Our study demonstrates that activation of the STING pathway holds the potential to initiate SS. Thus, apart from viral infections, conditions that cause cellular perturbations and accumulation of host DNA within the cytosol should also be considered as possible triggers for SS.

The Incredible Journey of Begomoviruses in Their Whitefly Vector.

Begomoviruses are vectored in a circulative persistent manner by the whitefly Bemisia tabaci. The insect ingests viral particles with its stylets. Virions pass along the food canal and reach the esophagus and the midgut. They cross the filter chamber and the midgut into the haemolymph, translocate into the primary salivary glands and are egested with the saliva into the plant phloem. Begomoviruses have to cross several barriers and checkpoints successfully, while interacting with would-be receptors and other whitefly proteins. The bulk of the virus remains associated with the midgut and the filter chamber. In these tissues, viral genomes, mainly from the tomato yellow leaf curl virus (TYLCV) family, may be transcribed and may replicate. However, at the same time, virus amounts peak, and the insect autophagic response is activated, which in turn inhibits replication and induces the destruction of the virus. Some begomoviruses invade tissues outside the circulative pathway, such as ovaries and fat cells. Autophagy limits the amounts of virus associated with these organs. In this review, we discuss the different sites begomoviruses need to cross to complete a successful circular infection, the role of the coat protein in this process and the sites that balance between virus accumulation and virus destruction.

PO-142: A 10-year review of primary major salivary glands carcinomas

PO-142: A 10-year review of primary major salivary glands carcinomas

Salivary gland morphology, tissue tropism and the progression of tospovirus infection in Frankliniella occidentalis

Tomato spotted wilt virus (TSWV) is transmitted by thrips in a propagative manner; however, progression of virus infection in the insect is not fully understood. The goal of this work was to study the morphology and infection of thrips salivary glands. The primary salivary glands (PSG) are complex, with three distinct regions that may have unique functions. Analysis of TSWV progression in thrips revealed the presence of viral proteins in the foregut, midgut, ligaments, tubular salivary glands (TSG), and efferent duct and filament structures connecting the TSG and PSG of first and second instar larvae. The primary site of virus infection shifted from the midgut and TSG in the larvae to the PSG in adults, suggesting that tissue tropism changes with insect development. TSG infection was detected in advance of PSG infection. These findings support the hypothesis that the TSG are involved in trafficking of TSWV to the PSG.

Quantification and localization of Watermelon chlorotic stunt virus and Tomato yellow leaf curl virus (Geminiviridae) in populations of Bemisia tabaci (Hemiptera, Aleyrodidae) with differential virus transmission characteristics.

Bemisia tabaci (Gennadius) is one of the economically most damaging insects to crops in tropical and subtropical regions. Severe damage is caused by feeding and more seriously by transmitting viruses. Those of the genus begomovirus (Geminiviridae) cause the most significant crop diseases and are transmitted by B. tabaci in a persistent circulative mode, a process which is largely unknown. To analyze the translocation and to identify critical determinants for transmission, two populations of B. tabaci MEAM1 were compared for transmitting Watermelon chlorotic stunt virus (WmCSV) and Tomato yellow leaf curl virus (TYLCV). Insect populations were chosen because of their high and respectively low virus transmission efficiency to compare uptake and translocation of virus through insects. Both populations harbored Rickettsia, Hamiltonella and Wolbachia in comparable ratios indicating that endosymbionts might not contribute to the different transmission rates. Quantification by qPCR revealed that WmCSV uptake and virus concentrations in midguts and primary salivary glands were generally higher than TYLCV due to higher virus contents of the source plants. Both viruses accumulated higher in insects from the efficiently compared to the poorly transmitting population. In the latter, virus translocation into the hemolymph was delayed and virus passage was impeded with limited numbers of viruses translocated. FISH analysis confirmed these results with similar virus distribution found in excised organs of both populations. No virus accumulation was found in the midgut lumen of the poor transmitter because of a restrained virus translocation. Results suggest that the poorly transmitting population comprised insects that lacked transmission competence. Those were selected to develop a population that lacks virus transmission. Investigations with insects lacking transmission showed that virus concentrations in midguts were reduced and only negligible virus amounts were found at the primary salivary glands indicating for a missing or modified receptor responsible for virus attachment or translocation.

Specific cells in the primary salivary glands of the whitefly Bemisia tabaci control retention and transmission of begomoviruses.

The majority of plant viruses are vectored by arthropods via persistent-circulative or noncirculative transmission. Previous studies have shown that specific binding sites for noncirculative viruses reside within the stylet or foregut of insect vectors, whereas the transmission mechanisms of circulative viruses remain ambiguous. Here we report the critical roles of whitefly primary salivary glands (PSGs) in the circulative transmission of two begomoviruses. The Middle East Asia Minor 1 (MEAM1) species of the whitefly Bemisia tabaci complex efficiently transmits both Tomato yellow leaf curl China virus (TYLCCNV) and Tomato yellow leaf curl virus (TYLCV), whereas the Mediterranean (MED) species transmits TYLCV but not TYLCCNV. PCR and fluorescence in situ hybridization experiments showed that TYLCCNV efficiently penetrates the PSGs of MEAM1 but not MED whiteflies. When a fragment of the coat protein of TYLCCNV was exchanged with that of TYLCV, mutated TYLCCNV accumulated in the PSGs of MED whiteflies, while mutant TYLCV was nearly undetectable. Confocal microscopy revealed that virion transport in PSGs follows specific paths to reach secretory cells in the central region, and the accumulation of virions in the secretory region of PSGs was correlated with successful virus transmission. Our findings demonstrate that whitefly PSGs, in particular the cells around the secretory region, control the specificity of begomovirus transmission. Over 75% of plant viruses are transmitted by insects. However, the mechanisms of virus transmission by insect vectors remain largely unknown. Begomoviruses and whiteflies are a complex of viruses and vectors which threaten many crops worldwide. We investigated the transmission of two begomoviruses by two whitefly species. We show that specific cells of the whitefly primary salivary glands control viral transmission specificity and that virion transport in the glands follows specific paths to reach secretory cells in the central region and then to reach the salivary duct. Our results indicate that the secretory cells in the central region of primary salivary glands determine the recognition and transmission of begomoviruses. These findings set a foundation for future research not only on circulative plant virus transmission but also on other human and animal viruses transmitted by arthropod vectors.

Analysis of the salivary gland transcriptome of Frankliniella occidentalis.

Saliva is known to play a crucial role in insect feeding behavior and virus transmission. Currently, little is known about the salivary glands and saliva of thrips, despite the fact that Frankliniella occidentalis (Pergande) (the western flower thrips) is a serious pest due to its destructive feeding, wide host range, and transmission of tospoviruses. As a first step towards characterizing thrips salivary gland functions, we sequenced the transcriptome of the primary salivary glands of F. occidentalis using short read sequencing (Illumina) technology. A de novo-assembled transcriptome revealed 31,392 high quality contigs with an average size of 605 bp. A total of 12,166 contigs had significant BLASTx or tBLASTx hits (E≤1.0E−6) to known proteins, whereas a high percentage (61.24%) of contigs had no apparent protein or nucleotide hits. Comparison of the F. occidentalis salivary gland transcriptome (sialotranscriptome) against a published F. occidentalis full body transcriptome assembled from Roche-454 reads revealed several contigs with putative annotations associated with salivary gland functions. KEGG pathway analysis of the sialotranscriptome revealed that the majority (18 out of the top 20 predicted KEGG pathways) of the salivary gland contig sequences match proteins involved in metabolism. We identified several genes likely to be involved in detoxification and inhibition of plant defense responses including aldehyde dehydrogenase, metalloprotease, glucose oxidase, glucose dehydrogenase, and regucalcin. We also identified several genes that may play a role in the extra-oral digestion of plant structural tissues including β-glucosidase and pectin lyase; and the extra-oral digestion of sugars, including α-amylase, maltase, sucrase, and α-glucosidase. This is the first analysis of a sialotranscriptome for any Thysanopteran species and it provides a foundational tool to further our understanding of how thrips interact with their plant hosts and the viruses they transmit.

A review of the mechanisms and components that determine the transmission efficiency of Tomato yellow leaf curl virus (Geminiviridae; Begomovirus) by its whitefly vector

Begomoviruses are a group of icosahedral single stranded DNA viruses exclusively transmitted by the sweet potato whitefly Bemisia tabaci in a persistent, circulative manner. In this mode of transmission, begomoviruses are acquired by their insect vector as intact virions from the plant phloem, move along the food canal, foregut and esophagus and reach the midgut where they are absorbed into the hemolymph via the filter chamber. The filter chamber is the site where most of the ingested food is filtered, and the first site where the majority of begomoviruses appear to be translocated into the hemolymph via unknown proteins or receptors. Transport from the filter chamber to the hemolymph is aided by a Heat Shock Protein 70. Virus particles not translocated across the filter chamber circulate in the midgut loop but it is not known whether absorption into the hemolymph occurs along this loop. Localization studies have confirmed that begomoviruses are not associated with the hindgut and absorption of virions in this organ is unlikely. In the hemolymph, virions have been shown to interact with a GroEL chaperone produced by the whitefly's endosymbiontic bacteria for ensuring their safe journey to the salivary glands. Virions penetrate the primary salivary glands via unknown proteins or receptors and are transported and secreted outside the whitefly to the plant with salivary secretions. Several recent studies have demonstrated the implications of insect and endosymbiont proteins such as the heat shock protein 70 and the bacterial GroEL protein, in the transmission of begomoviruses by B. tabaci. Additional studies attempting to identify other proteins that aid or interact with begomoviruses along their circulation pathway in the whitefly are reviewed in this paper.