An Insight Into The MicroRNA Profiles of An Ectoparasite Mite Varroa Destructor (Acari: Varroidae), The Primary Vector of Deformed Wing Virus (DWV) of The Honey Bee

The most important ectoparasite of the honeybee is the remarkably adaptive mite Varroa destructor. The Varroa mite is a competent vector of Deformed Wing Virus (DWV), the Varroa-virus complex is one of the main factors associated with elevated annual honey bee colony mortality. Micro-RNAs (miRNAs) are small, non-coding RNAs of ~22-24 nucleotides, produced by all plants, animals, and viruses that influence biological processes through post-transcriptional regulation of gene expression. Knowledge of miRNAs and their functional role in mite biology remains limited. This study developed small RNA libraries from male and female V. destructor by utilizing Illumina's small RNA-Seq platform. A total of 101,913,208 and 91,904,732 small RNA reads (>18 nucleotides) from male and female mites were analyzed using the mirDeep2 algorithm. A conservative approach predicted a total of 306 miRNAs, of which 18 were upregulated and 13 were downregulated in female V. destructor compared to males. A qPCR assay validated the expression of selected differentially expressed female Varroa miRNAs. This dataset provides a list of potential miRNA targets involved in regulating vital Varroa biological processes and for deciphering new targets against Varroa and honey bee viruses they carry.

High-resolution asymmetric structure of a Fab–virus complex reveals overlap with the receptor binding site

Canine parvovirus is an important pathogen causing severe diseases in dogs, including acute hemorrhagic enteritis, myocarditis, and cerebellar disease. Overlap on the surface of parvovirus capsids between the antigenic epitope and the receptor binding site has contributed to cross-species transmission, giving rise to closely related variants. It has been shown that Mab 14 strongly binds and neutralizes canine but not feline parvovirus, suggesting this antigenic site also controls species-specific receptor binding. To visualize the conformational epitope at high resolution, we solved the cryogenic electron microscopy (cryo-EM) structure of the Fab–virus complex. We also created custom software, Icosahedral Subparticle Extraction and Correlated Classification, to solve a Fab–virus complex with only a few Fab bound per capsid and visualize local structures of the Fab-bound and -unbound antigenic sites extracted from the same complex map. Our results identified the antigenic epitope that had significant overlap with the receptor binding site, and the structures revealed that binding of Fab induced conformational changes to the virus. We were also able to assign the order and position of attached Fabs to allow assessment of complementarity between the Fabs bound to different positions. This approach therefore provides a method for using cryo-EM to investigate complementarity of antibody binding.

Field Screen and Genotyping of Phaseolus vulgaris against Two Begomoviruses in Georgia, USA

The production and quality of Phaseolusvulgaris (snap bean) have been negatively impacted by leaf crumple disease caused by two whitefly-transmitted begomoviruses: cucurbit leaf crumple virus (CuLCrV) and sida golden mosaic Florida virus (SiGMFV), which often appear as a mixed infection in Georgia. Host resistance is the most economical management strategy against whitefly-transmitted viruses. Currently, information is not available with respect to resistance to these two viruses in commercial cultivars. In two field seasons (2018 and 2019), we screened Phaseolus spp. genotypes (n = 84 in 2018; n = 80 in 2019; most of the genotypes were common in both years with a few exceptions) for resistance against CuLCrV and/or SiGMFV. We also included two commonly grown Lima bean (Phaseolus lunatus) varieties in our field screening. Twenty Phaseolus spp. genotypes with high to moderate-levels of resistance (disease severity ranging from 5%–50%) to CuLCrV and/or SiGMFV were identified. Twenty-one Phaseolus spp. genotypes were found to be highly susceptible with a disease severity of ≥66%. Furthermore, based on the greenhouse evaluation with two genotypes-each (two susceptible and two resistant; identified in field screen) exposed to viruliferous whiteflies infected with CuLCrV and SiGMFV, we observed that the susceptible genotypes accumulated higher copy numbers of both viruses and displayed severe crumple severity compared to the resistant genotypes, indicating that resistance might potentially be against the virus complex rather than against the whiteflies. Adult whitefly counts differed significantly among Phaseolus genotypes in both years. The whole genome of these Phaseolus spp. [snap bean (n = 82); Lima bean (n = 2)] genotypes was sequenced and genetic variability among them was identified. Over 900 giga-base (Gb) of filtered data were generated and >88% of the resulting data were mapped to the reference genome, and SNP and Indel variants in Phaseolus spp. genotypes were obtained. A total of 645,729 SNPs and 68,713 Indels, including 30,169 insertions and 38,543 deletions, were identified, which were distributed in 11 chromosomes with chromosome 02 harboring the maximum number of variants. This phenotypic and genotypic information will be helpful in genome-wide association studies that will aid in identifying the genetic basis of resistance to these begomoviruses in Phaseolus spp.

First Record of Mosquito-Borne Kyzylagach Virus in Central Europe

RNA of Kyzylagach virus (KYZV), a Sindbis-like mosquito-borne alphavirus from Western equine encephalitis virus complex, was detected in four pools (out of 221 pools examined), encompassing 10,784 female Culex modestus mosquitoes collected at a fishpond in south Moravia, Czech Republic, with a minimum infection rate of 0.04%. This alphavirus was never detected in Central Europe before.

MicroRNAs Are Predicted to Control the Ubiquitin/Proteasome System in Carica papaya Plants Infected by the Papaya Meleira Virus Complex

Papaya sticky disease (PSD) is a severe disease that can destroy papaya trees. PSD is associated with a complex formed between a toti-like virus, Papaya meleira virus (PMeV), and an umbra-like virus—Papaya meleira virus 2 (PMeV2). PSD symptoms only appear after flowering, indicating that at the pre-flowering stage, there is a host stress response associated with tolerance to sticky disease symptoms. Transcriptomic and proteomic analyses of symptomatic plants revealed the modulation of protein turnover, suggesting the involvement of the ubiquitin/proteasome system (UPS) in this pathosystem. In parallel, the analysis of microRNAs modulated during the infection showed that microRNAs predicted to target UPS genes were specially altered. This study aimed to evaluate the importance of UPS for C. papaya–PMeV complex interaction by revisiting transcriptomic and proteomic datasets obtained from infected plants at different developmental phases. In the referred datasets, 1074 transcripts and 80 proteins were related to the UPS pathway. Among the 42 UPS-related genes responsive to PSD, 22 were detected at the transcript level and 21 at the protein level. In addition, the microRNAs predicted to target UPS-related genes were identified, especially those altered during papaya infection by PMeV complex. A total of 106 miRNAs assigned to 33 miRNA families and targeting 146 gene transcripts were found. Among them, 22 miRNAs were predicted to target four genes (U-box domain-containing protein, protein with BTB/POZ domains, 26S proteasome regulatory complex subunit PSMD10, and zinc finger C2H2 type domain) that were observed to be modulated at the transcript level at the pre-flowering stage and one gene (ubiquitin binding domain protein) modulated at the protein level at the post-flowering stage. Experimental evidence supports the idea that key miRNAs were especially relevant in controlling UPS during C. papaya response to the PMeV complex. The miRNA expression and the consequent reduction in transcripts levels could result in increased PMeV complex tolerance in C. papaya. The results presented here add to the knowledge on UPS involvement during virus infection in plants.