The Role of Extensive Recombination in the Evolution of Geminiviruses.

Mutation, recombination and pseudo-recombination are the major forces driving the evolution of viruses by the generation of variants upon which natural selection, genetic drift and gene flow can act to shape the genetic structure of viral populations. Recombination between related virus genomes co-infecting the same cell usually occurs via template swapping during the replication process and produces a chimeric genome. The family Geminiviridae shows the highest evolutionary success among plant virus families, and the common presence of recombination signatures in their genomes reveals a key role in their evolution. This review describes the general characteristics of members of the family Geminiviridae and associated DNA satellites, as well as the extensive occurrence of recombination at all taxonomic levels, from strain to family. The review also presents an overview of the recombination patterns observed in nature that provide some clues regarding the mechanisms involved in the generation and emergence of recombinant genomes. Moreover, the results of experimental evolution studies that support some of the conclusions obtained in descriptive or in silico works are summarized. Finally, the review uses a number of case studies to illustrate those recombination events with evolutionary and pathological implications as well as recombination events in which DNA satellites are involved.

Telomerase RNA recruits RNA polymerase II to target gene promoters to enhance myelopoiesis.

Dyskeratosis congenita (DC) is a rare inherited bone marrow failure and cancer predisposition syndrome caused by mutations in telomerase or telomeric proteins. Here, we report that zebrafish telomerase RNA (terc) binds to specific DNA sequences of master myeloid genes and controls their expression by recruiting RNA Polymerase II (Pol II). Zebrafish terc harboring the CR4-CR5 domain mutation found in DC patients hardly interacted with Pol II and failed to regulate myeloid gene expression in vivo and to increase their transcription rates in vitro. Similarly, TERC regulated myeloid gene expression and Pol II promoter occupancy in human myeloid progenitor cells. Strikingly, induced pluripotent stem cells derived from DC patients with a TERC mutation in the CR4-CR5 domain showed impaired myelopoiesis, while those with mutated telomerase catalytic subunit differentiated normally. Our findings show that TERC acts as a transcription factor, revealing a target for therapeutic intervention in DC patients.

Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors.

BACKGROUND: The group of > 40 cryptic whitefly species called Bemisia tabaci sensu lato are amongst the world's worst agricultural pests and plant-virus vectors. Outbreaks of B. tabaci s.l. and the associated plant-virus diseases continue to contribute to global food insecurity and social instability, particularly in sub-Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the 'Ensembl gene annotation system', to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification. RESULTS: We present here six new B. tabaci s.l. genomes from Africa and Asia, and two re-annotated previously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616-658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8-13.2 × 103 PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda-1 to the sub-Saharan group of species. Reciprocal cross-mating data and the co-cladogenesis pattern of the primary obligate endosymbiont 'Candidatus Portiera aleyrodidarum' from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species. CONCLUSIONS: These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post-genomic research, including the selection of candidate gene-targets for innovative whitefly and virus-control strategies.

Subclinical Left Ventricular Systolic Dysfunction in Hospitalized Patients with COVID-19 by Strain: A 30-Day Echocardiographic Follow-Up.

Background and Objectives: Available studies confirm myocardial injury and its association with mortality in patients with COVID-19, but few data have been reported from echocardiographic studies. The aim of this study was to identify subclinical left ventricular dysfunction by global longitudinal strain (GLS) and its evolution in the short term in hospitalized patients with COVID-19. Materials and Methods: Thirty-one consecutive noncritical patients admitted for COVID-19 were included. Information on demographics, laboratory results, comorbidities, and medications was collected. Transthoracic echocardiograms were performed using a Philips Affinity 50, at the acute stage and at a 30-day follow-up. Automated left ventricular GLS was measured using a Philips Qlab 13.0. A GLS of <-15.9% was defined as abnormal. Results: The mean age was 65 ± 15.2 years, and 61.3% of patients were male. Nine patients (29%) had elevated levels of high-sensitivity troponin I. Left ventricular ejection fraction was preserved in all; however, 11 of them (35.5%) showed reduced GLS. These patients had higher troponin levels (median, 23.7 vs. 3.2 ng/L; p < 0.05) and NT-proBNP (median, 753 vs. 81 pg/mL; p < 0.05). The multivariate analysis revealed that myocardial injury, defined as increased troponin, was significantly associated with GLS values (coefficient B; p < 0.05). Follow-up at 30 days showed an improvement in GLS values in patients with subclinical left ventricular dysfunction (-16.4 ± 2.07% vs. -13.2 ± 2.40%; p < 0.01), without changes in the normal GLS group. Conclusions: Subclinical left ventricular dysfunction is common in noncritical hospitalized patients with COVID-19 (one in every three patients), even with preserved left ventricular ejection fraction. This impairment tends to be reversible on clinical recovery.

[Esophageal foreign bodies: review of 84 cases]. / Cuerpos extraños en esófago: revisión de 84 casos.

The presence of esophageal foreign body (EFB) is a common emergency in gastroenterology. The protocol for management and endoscopic intervention can be variable among institutions. OBJECTIVE: to define the clinical characteristics of EFB in adults, its radiological and endoscopic diagnosis, and complications based on a sample of patients in a gastroenterology center. MATERIALS AND METHODS: case series of patients admitted from the emergency department and referred to the gastroenterology department with a presumptive diagnosis of EFB. Clinical variables were collected, as well as characteristics, comorbidities, time of evolution and diagnostic opportunity, confirmatory studies, and complications. RESULTS: 84 subjects, 70% men, mean age 45 (range: 17-87; SD 12.5) years. Urgent upper endoscopy was performed in 98.8% of the patients, with an average in-hospital stay of 2.5 days. 93% had no associated underlying pathology, in 6/84 (7.14%) patients structural or functional esophageal pathology was documented. 59/84 (70.2%) patients consulted in the first 24 hours, in 57.6% the presence of foreign body was confirmed endoscopically. In 67/84 (79.76%) patients radiography was performed prior to endoscopy, of which 62/67 (92.5%) had an abnormal result. Seventy percent of confirmed EFB were fish bones. The most frequent site of localization was in the cricopharyngeal region in 90% of the cases. In 66/84 (78.6%) subjects there was absence of complications, followed by deep laceration in 10/84 (11.9%) cases. In 3/84 (3.6%) cases complications requiring surgery were identified. CONCLUSIONS: Endoscopic intervention in the first 24 hours is an opportune moment to identify complications and provide the indicated treatment.

Germination niche breadth of invasive Iris pseudacorus (L.) suggests continued recruitment from seeds with global warming.

PREMISE: Understanding recruitment processes of invasive species is central to conservation and management strategies. Iris pseudacorus, an emergent macrophyte, has established invasive populations across a broad global range, and reduces biodiversity in wetland ecosystems. Climate change is altering germination cues, yet studies on the invasion of wetland macrophytes often ignore germination ecology despite its importance to their establishment and spread. METHODS: We explored germination of seeds from invasive I. pseudacorus populations in California in response to seed coat presence or absence, and several environmental factors. Using experimental results in a thermal time model, we derived germination temperature thresholds. RESULTS: Germination of I. pseudacorus seeds did not require cold or warm stratification, and was not affected by seed coat presence or absence. Germination occurred in the dark, although germinability was two- to threefold times greater under light. At constant temperature, thermal time model estimates included 18.3 ± 1.8°C base germination temperature (Tb$({T}_{b}$ ); 28.2 ± 0.5°C optimal temperature (To$({T}_{o}$ ); and 41.0 ± 1.7°C ceiling temperature (Tc$({T}_{c}$ ). Seeds exposed to 36.0°C achieved over 10% germination, and embryos of ungerminated seeds presented 76% viability. Overall, germinability remained relatively low at constant temperatures (≤25%) but was close to 90% under alternating daily temperatures. CONCLUSIONS: Exposure to diurnally fluctuating temperatures is essential for this species to achieve high germination rates. Our study reveals that I. pseudacorus has a broad germination niche supporting its establishment in a relatively wide range of environments, including at high temperatures more frequent with climate change.

Establishment of five new genera in the family Geminiviridae: Citlodavirus, Maldovirus, Mulcrilevirus, Opunvirus, and Topilevirus.

Geminiviruses are plant-infecting, circular single-stranded DNA viruses that have a geminate virion morphology. These viruses infect both cultivated and non-cultivated monocotyledonous and dicotyledonous plants and have a wide geographical distribution. Nine genera had been established within the family Geminiviridae (Becurtovirus, Begomovirus, Capulavirus, Curtovirus, Eragrovirus, Grablovirus, Mastrevirus, Topocuvirus, and Turncurtovirus) as of 2020. In the last decade, metagenomics approaches have facilitated the discovery and identification of many novel viruses, among them numerous highly divergent geminiviruses. Here, we report the establishment of five new genera in the family Geminiviridae (Citlodavirus, Maldovirus, Mulcrilevirus, Opunvirus, and Topilevirus) to formally classify twelve new, divergent geminiviruses.

[Experience with digital peroral cholangioscopy using SpyGlass DS in different reference centers in gastroenterology and digestive endoscopy in Colombia: Case series]. / Experiencia en colangioscopia digital peroral con SpyGlass DS en diferentes centros de referencia en gastroenterología y endoscopia digestiva en Colombia: Serie de casos.

SpyGlass DS is a peroral cholangioscopy system, associated with improved image quality and configuration. Currently, there is diversity in its use and little information on its implementation, including clinical outcomes and adverse events. To describe the experience of using SpyGlass DS in several gastroenterology reference centres in Colombia, mentioning efficacy and possible adverse events. This is an observational study (case series). The main indication was choledocholithiasis (n:204), followed by biliary stricture (n:40) and pancreatolithiasis (n:16). 49.2% were male, mean age 58.6 years, clinically with predominance of abdominal pain (80.5%) and jaundice (86.1%). All cases had previous imaging (CT scan, MRI or ultrasound), 98.07% previous endoscopic retrograde cholangiopancreatography (n:255) and 75% biliary plastic stent. Laser was used in 78/220 patients and electrohydraulic lithotripsy in 142/220 patients, with single-session resolution rates of 96.15% and 95.07%, respectively. Seven cases required a second lithotripsy session and 3 patients required surgical management, one for pancreatolithiasis with basal pancreas divisum and 2 for hepatolithiasis. 40/260 patients presented with biliary stricture, 32/40 with malignant findings (cholangiocarcinoma) and 8/40 with benign pathology (primary sclerosing cholangitis, non-specific inflammatory changes) after histopathological studies. As complications, 6 cases of bacteraemia (2.5%) were recorded, being more frequent in cases of stenosis. The mean postoperative stay was 2.04 days. We concluded that the use of SpyGlass DS is feasible in our setting, being effective for diagnosis and treatment of biliary lesions, and with low risk of adverse events.

ICTV Virus Taxonomy Profile: Geminiviridae 2021.

The family Geminiviridae includes viruses with mono- or bipartite single-stranded, circular DNA genomes of 2.5-5.2 kb. They cause economically important diseases in most tropical and subtropical regions of the world. Geminiviruses infect dicot and monocot plants and are transmitted by insect vectors. DNA satellites are associated with some geminiviruses. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Geminiviridae which is available at ictv.global/report/geminiviridae.

Merkel cell carcinoma in Latin America: a contribution from an expanded access program for avelumab to address issues from experts' recommendations.

BACKGROUND: Merkel cell carcinoma (MCC) is an aggressive malignancy, associated with poor outcomes in patients with metastatic disease (mMCC). Management has been dramatically altered as a result of incorporating immune checkpoint blockade agents. MCC data from Latin America (LATAM) come from case-series or individual records. Regional registries are lacking. A need for better registries to improve current knowledge about MCC is highlighted. Our objectives were to describe a real-world experience with avelumab as a second-line (or first-line in unfit patients) treatment in a subset of LATAM participants enrolled in a global Expanded Access Program (EAP) for patients with mMCC, and to evaluate its contribution to the resolution of the concerns described in a recent regional experts review. MATERIALS AND METHODS: We reviewed data of LATAM participants in an avelumab EAP for mMCC treatment (NCT03089658). EAP patient had unresectable or mMCC with progressive disease after one line of chemotherapy, and were ineligible for clinical trials or unfit for chemotherapy. RESULTS: 46 patients (median age: 71.6 years; 60.9% males; median treatment duration: 7.9 months) were included in the LATAM EAP. Physician-assessed objective responses were available for 19 patients. Complete response rate was 15.8% and partial response rate reached 42.1%, summarizing an objective response rate of 57.9%. Stable disease rate was 10.5%, with a disease control response of 68.4%. CONCLUSION: Avelumab showed robust efficacy and a safety profile consistent with global EAP data. Results are aimed to improve current knowledge about mMCC treatment and access to immunooncologic strategies for treating LATAM patients.

Tomato chlorosis virus-encoded p22 suppresses auxin signalling to promote infection via interference with SKP1-Cullin-F-boxTIR1 complex assembly.

Phytohormone auxin plays a fundamental role in plant growth and defense against pathogens. However, how auxin signalling is regulated during virus infection in plants remains largely unknown. Auxin/indole-3-acetic acid (Aux/IAA) is the repressor of auxin signalling and can be recognized by an F-box protein transport inhibitor response 1 (TIR1). Ubiquitination and degradation of Aux/IAA by SKP1-Cullin-F-boxTIR1 (SCFTIR1 ) complex can trigger auxin signalling. Here, with an emerging important plant virus worldwide, we showed that tomato chlorosis virus (ToCV) infection or stable transgenic overexpression of its p22 protein does not alter auxin accumulation level but significantly decreases the expression of auxin signalling-responsive genes, suggesting that p22 can attenuate host auxin signalling. Further, p22 could bind the C-terminal of SKP1.1 and compete with TIR1 to interfere with the SCFTIR1 complex assembly, leading to a suppression of Aux/IAA degradation. Silencing and over-expression assays suggested that both NbSKP1.1 and NbTIR1 suppress ToCV accumulation and disease symptoms. Altogether, ToCV p22 disrupts the auxin signalling through destabilizing SCFTIR1 by interacting with the C-terminal of NbSKP1.1 to promote ToCV infection. Our findings uncovered a previously unknown molecular mechanism employed by a plant virus to manipulate SCF complex-mediated ubiquitin pathway and to reprogram auxin signalling for efficient infection.

Digital Quantification of Ki-67 and PHH3 in the Classification of Uterine Smooth Muscle Tumors.

Uterine smooth muscle tumors are the most common tumors of the female genital tract and include leiomyoma (LM) and its variants, smooth muscle tumors of uncertain malignant potential (STUMP), and leiomyosarcoma (LMS). Accurate diagnosis of LMS is determined by nuclear atypia, mitotic count, and the presence or absence of tumor cell necrosis, a process which is often difficult and subjective. In this study, we correlated digital quantification of proliferation marker Ki-67 and mitotic marker phosphohistone H3 (PHH3) to mitotic count, classification of uterine smooth muscle tumors, and clinical outcomes. A total of 39 cases (17 LMS, 5 STUMP, 10 LM with bizarre nuclei, and 7 LM) were included. Mitotic count, Ki-67, and PHH3 were significantly correlated. When comparing the LMS group to the STUMP, LM with bizarre nuclei, and LM groups combined, LMS showed a significantly greater digital quantification of Ki-67 (median 10.6% vs. 0.4%, P<0.001) and PHH3 (median 0.5% vs. 0.14%, P=0.022). Ki-67 was a better predictor of LMS compared with PHH3 (area under the curve 0.92 vs. 0.73, P=0.017). Above a threshold Ki-67 value of 3.8%, the sensitivity was 82% and specificity was 91%. Clinical outcomes were available for 10 patients (8 LMS and 2 STUMP), and inferior progression-free survival was noted for patients with higher Ki-67 values. Overall, this study suggests that digital quantification of Ki-67 can potentially aid in diagnosis of LMS.

Taxonomy update for the family Alphasatellitidae: new subfamily, genera, and species.

Alphasatellites (family Alphasatellitidae) are circular, single-stranded DNA molecules (~1-1.4 kb) that encode a replication-associated protein and have commonly been associated with some members of the families Geminiviridae, Nanoviridae, and Metaxyviridae (recently established). Here, we provide a taxonomy update for the family Alphasatellitidae following the International Committee on Taxonomy of Viruses (ICTV) Ratification Vote held in March 2021. The taxonomic update includes the establishment of the new subfamily Petromoalphasatellitinae. This new subfamily includes three new genera as well as the genus Babusatellite, which previously belonged to the subfamily Nanoalphasatellitinae. Additionally, three new genera and 14 new species have been established in the subfamily Geminialphasatellitinae, as well as five new species in the subfamily Nanoalphasatellitinae.

Expression of p40 in Primary Cutaneous Mucinous Carcinoma Versus Primary Mucinous Carcinomas of the Breast and Colon.

BACKGROUND: The transcription factor p63 is a homolog of p53, expressed in basal layers of epithelia and myoepithelial cells. Some studies have suggested that p63 may provide utility in differentiating primary versus metastatic mucinous carcinoma of the skin, given its preferential expression in primary adnexal neoplasms. There have been few studies investigating the expression patterns of p40, an isoform of p63, in primary cutaneous mucinous carcinomas. METHODS: An immunohistochemical panel including p40, CK7, CK20, estrogen receptor, and progesterone receptor was applied to primary mucinous carcinomas of the skin, breast, and colon. RESULTS: Only a small subset (25%) of primary cutaneous mucinous carcinomas displayed focal positive staining with p40, similar to what has been reported in the literature for p63. All primary mucinous carcinomas of skin and breast labeled positively with CK7, estrogen receptor, and progesterone receptor. Primary colon mucinous carcinomas were only positive for CK20. CONCLUSIONS: Based on these results, p40 seems to be an insufficient marker for distinguishing primary versus metastatic mucinous carcinoma due to its low rate of positivity in primary cutaneous mucinous carcinomas.

Theoretical Prediction of Structures, Vibrational Circular Dichroism, and Infrared Spectra of Chiral Be4B8 Cluster at Different Temperatures.

Lowest-energy structures, the distribution of isomers, and their molecular properties depend significantly on geometry and temperature. Total energy computations using DFT methodology are typically carried out at a temperature of zero K; thereby, entropic contributions to the total energy are neglected, even though functional materials work at finite temperatures. In the present study, the probability of the occurrence of one particular Be4B8 isomer at temperature T is estimated by employing Gibbs free energy computed within the framework of quantum statistical mechanics and nanothermodynamics. To identify a list of all possible low-energy chiral and achiral structures, an exhaustive and efficient exploration of the potential/free energy surfaces is carried out using a multi-level multistep global genetic algorithm search coupled with DFT. In addition, we discuss the energetic ordering of structures computed at the DFT level against single-point energy calculations at the CCSD(T) level of theory. The total VCD/IR spectra as a function of temperature are computed using each isomer's probability of occurrence in a Boltzmann-weighted superposition of each isomer's spectrum. Additionally, we present chemical bonding analysis using the adaptive natural density partitioning method in the chiral putative global minimum. The transition state structures and the enantiomer-enantiomer and enantiomer-achiral activation energies as a function of temperature evidence that a change from an endergonic to an exergonic type of reaction occurs at a temperature of 739 K.

Effects of Temperature on Enantiomerization Energy and Distribution of Isomers in the Chiral Cu13 Cluster.

In this study, we report the lowest energy structure of bare Cu13 nanoclusters as a pair of enantiomers at room temperature. Moreover, we compute the enantiomerization energy for the interconversion from minus to plus structures in the chiral putative global minimum for temperatures ranging from 20 to 1300 K. Additionally, employing nanothermodynamics, we compute the probabilities of occurrence for each particular isomer as a function of temperature. To achieve that, we explore the free energy surface of the Cu13 cluster, employing a genetic algorithm coupled with density functional theory. Moreover, we discuss the energetic ordering of isomers computed with various density functionals. Based on the computed thermal population, our results show that the chiral putative global minimum strongly dominates at room temperature.

Interactive effects of salinity and inundation on native Spartina foliosa, invasive S. densiflora and their hybrid from San Francisco Estuary, California.

BACKGROUND AND AIMS: Sea level rise (SLR) associated with climate change is intensifying permanent submersion and salinity in salt marshes. In this scenario, hybridization between native and invasive species may result in hybrids having greater tolerance of abiotic stress factors than their parents. Thus, understanding the responses of native and invasive halophytes and their hybrids to interacting physiological stresses imposed by SLR is key to native species conservation. We analysed how salinity, inundation depth and their interaction impact the functional traits of native and invasive cordgrass species and their hybrid (genus Spartina; Poaceae). METHODS: In a mesocosm experiment, we evaluated interactive stress effects of three inundation depths (4.5, 35.5 and 55 cm) and four aqueous salinities (0.5, 10, 20 and 40 ppt) on 27 functional traits of native Spartina foliosa, invasive S. densiflora and their hybrid S. densiflora × S. foliosa from San Francisco Estuary. KEY RESULTS: The combined effect of salinity and inundation led to synergistic effects on leaf biochemical stress indicators. Spartina foliosa behaved as a stress-tolerant species, with high leaf sodium exudation rate and glycine betaine concentrations that also increased with stress. Spartina foliosa was less sensitive to salinity than S. densiflora and the hybrid but was highly growth-limited in response to increased inundation and salinity. Spartina densiflora was fast-growing in low-stress conditions and tolerated moderate interactive stresses. The hybrid produced more biomass, rhizome reserves and tillers than its parents, even under the most stressful conditions. Transgressivity improved the hybrid's capacity to deal with flooding stress more so than its response to increasing salinity. CONCLUSIONS: Based on our observations, we predict that established populations of both native and invasive cordgrasses will experience reduced vegetative and sexual fitness in response to SLR. In particular, the combined effects of high salinity and deep inundation may decrease floret production in S. densiflora, a key trait for the spread of its invasive populations. In contrast, the hybrid likely will be able to sustain its invasiveness under SLR based on its ability to maintain growth and biomass production under stressful conditions.

Changes to the functional traits of phosphoenolpyruvate carboxylase following hybridization in C-4 halophytes.

Hybridization is a relevant evolutionary mechanism linked to the invasiveness of plant species, but little is known about its effect on enzymatic activities in response to stress. We analyzed the effects of salinity on key mechanistic traits of phosphoenolpyruvate carboxylase (PEPC) enzyme for two hybrid taxa derived from native Spartina maritima (Curtis) Fernald and invasive Spartina densiflora Brongn. in comparison with their parental species. Parental species showed contrasted strategies at the PEPC level to cope with salinity. Spartina maritima showed its physiological optimum at 10 to 40 ppt salinity, with high PEPC activity (per unit leaf soluble protein), in contrast to the lower salinity optimum of 0.5 and 10 ppt for S. densiflora, where highest levels of PEPC apparent specific activity coincided with high light-induced activation of PEPC. Both hybrids showed constant PEPC apparent specific activity from fresh water to hypersalinity and exhibited higher net photosynthesis rates in fresh water than their parents. Spartina maritima × densiflora presented three transgressive PEPC-related traits, being the only taxon able to increase its PEPC activation in darkness at high salinity. Spartina densiflora × maritima showed most PEPC-related traits intermediate between its parents. Inheritance types operating differently in reciprocal hybrids determine key functional traits conditioning their ecological performance.

Transmission of Begomoviruses and Other Whitefly-Borne Viruses: Dependence on the Vector Species.

Most plant viruses require a biological vector to spread from plant to plant in nature. Among biological vectors for plant viruses, hemipteroid insects are the most common, including phloem-feeding aphids, whiteflies, mealybugs, planthoppers, and leafhoppers. A majority of the emerging diseases challenging agriculture worldwide are insect borne, with those transmitted by whiteflies (Hemiptera: Aleyrodidae) topping the list. Most damaging whitefly-transmitted viruses include begomoviruses (Geminiviridae), criniviruses (Closteroviridae), and torradoviruses (Secoviridae). Among the whitefly vectors, Bemisia tabaci, now recognized as a complex of cryptic species, is the most harmful in terms of virus transmission. Here, we review the available information on the differential transmission efficiency of begomoviruses and other whitefly-borne viruses by different species of whiteflies, including the cryptic species of the B. tabaci complex. In addition, we summarize the factors affecting transmission of viruses by whiteflies and point out some future research prospects.

Fundamental Aspects of Plant Viruses-An Overview on Focus Issue Articles.

Given the importance of and rapid research progress in plant virology in recent years, this Focus Issue broadly emphasizes advances in fundamental aspects of virus infection cycles and epidemiology. This Focus Issue comprises three review articles and 18 research articles. The research articles cover broad research areas on the identification of novel viruses, the development of detection methods, reverse genetics systems and functional genomics for plant viruses, vector and seed transmission studies, viral population studies, virus-virus interactions and their effect on vector transmission, and management strategies of viral diseases. The three review articles discuss recent developments in application of prokaryotic clustered regularly interspaced short palindromic repeats/CRISPR-associated genes (CRISPR/Cas) technology for plant virus resistance, mixed viral infections and their role in disease synergism and cross-protection, and viral transmission by whiteflies. The following briefly summarizes the articles appearing in this Focus Issue.