The transmission mode of grapevine red blotch virus (GRBV, genus Grablovirus, family Geminiviridae) by Spissistilus festinus, the three-cornered alfalfa hopper, is unknown. By analogy with other members in the family Geminiviridae, we hypothesized circulative, nonpropagative transmission. Time-course experiments revealed GRBV in dissected guts, hemolymph, and heads with salivary glands after a 5-, 8-, and 10-day exposure to infected grapevines, respectively. After a 15-day acquisition on infected grapevines and subsequent transfer on alfalfa, a nonhost of GRBV, the virus titer decreased over time in adult insects, as shown by quantitative PCR. Snap bean proved to be a feeding host of S. festinus and a pseudosystemic host of GRBV after Agrobacterium tumefaciens-mediated delivery of an infectious clone. The virus was efficiently transmitted by S. festinus from infected snap bean plants to excised snap bean trifoliates (90%) or grapevine leaves (100%) but less efficiently from infected grapevine plants to excised grapevine leaves (10%) or snap bean trifoliates (67%). Transmission of GRBV also occurred trans-stadially but not via seeds. The virus titer was significantly higher in (i) guts and hemolymph relative to heads with salivary glands, and (ii) adults emanating from third compared with first instars that emerged on infected grapevine plants and developed on snap bean trifoliates. This study demonstrated circulative, nonpropagative transmission of GRBV by S. festinus with an extended acquisition access period compared with other viruses in the family Geminiviridae and marked differences in transmission efficiency between grapevine, the natural host, and snap bean, an alternative herbaceous host.

Glutathione is an important biological molecule which can be an indicator of numerous diseases. A method for self-powered detection of glutathione levels in solution has been developed using an enzymatic biofuel cell. The device consists of a glucose oxidase anode and a bilirubin oxidase cathode. For the detection of glutathione, the inhibition of bilirubin oxidase leads to a measurable decrease in current and power output. The reported method has a detection limit of 0.043 mM and a linear range up to 1.7 mM. Being able to detect a range of concentrations can be useful in evaluating a patient’s health. This method has the potential to be implemented as a quick, low-cost alternative to previously reported methods.

Viruses can elicit varying types and severities of symptoms during plant host infection. We investigated changes in the proteome and transcriptome of Nicotiana benthamiana plants infected by grapevine fanleaf virus (GFLV) with an emphasis on vein clearing symptom development. Comparative, time-course liquid chromatography tandem mass spectrometry and 3' ribonucleic acid sequencing analyses of plants infected by two wildtype GFLV strains, one symptomatic and one asymptomatic, and their asymptomatic mutant strains carrying a single amino acid change in the RNA-dependent RNA polymerase (RdRP) were conducted to identify host biochemical pathways involved in viral symptom development. During peak vein clearing symptom display at 7 days post-inoculation (dpi), protein and gene ontologies related to immune response, gene regulation, and secondary metabolite production were overrepresented when contrasting wildtype GFLV strain GHu and mutant GHu-1E_K802G^Pol. Prior to the onset of symptom development at 4 dpi and when symptoms faded away at 12 dpi, protein and gene ontologies related to chitinase activity, hypersensitive response, and transcriptional regulation were identified. This systems biology approach highlighted how a single amino acid of a plant viral RdRP mediates changes to the host proteome (∼1%) and transcriptome (∼8.5%) related to transient vein clearing symptoms and the network of pathways involved in the virus-host arms race.

Grapevine red blotch is an emerging disease that threatens vineyard productions in North America. Grapevine red blotch virus (GRBV, species Grablovirus vitis, genus Grablovirus, family Geminiviridae), the causal agent of red blotch disease, is transmitted by Spissistilus festinus (Hemiptera: Membracidae) in a circulative, non-propagative mode. To gain new insight into GRBV-S. festinus interactions, we delved into vertical transmission and documented a lack of transovarial transmission. In addition, we investigated S. festinus sex differences in the horizontal transmission of GRBV by creating small arenas with 30 detached trifoliates of common snap bean, an experimental host of GRBV, and a preferred feeding host of S. festinus. Tracking the movement of viruliferous males, females, or a combination of the two sexes over two weeks in replicated experiments demonstrated that male S. festinus dispersed more than females with specimens of both sexes predominantly grouping together on trifoliates spatially surrounding the trifoliate onto which they were released. These behaviors resulted in a greater rate of GRBV transmission by S. festinus males (17%, 20 of 120) than females (4%, 5 of 120) or mixed-sex cohorts (9%, 17 of 180). In arenas with aviruliferous S. festinus and one (single) or four (hotspot) GRBV-infected trifoliates out of 30 total trifoliates, a higher GRBV transmission rate by males was confirmed in both single infection (50%, 30 of 60) and hotspot infection (83%, 50 of 60) arenas than by females in single infection (35%, 21 of 60) and hotspot infection (67%, 40 of 60) arenas. These findings highlighted sex-associated differences in the transmission of GRBV by S. festinus and a positive correlation between the initial virus prevalence and the rate of transmission. Finally, the secondary spread of GRBV resulted primarily from S. festinus dispersal by walking or jumping. Together, these unique GRBV transmission features support the need to characterize dispersal behaviors of S. festinus in vineyard ecosystems.

Plant virus genomes encode proteins that are involved in replication, encapsidation, cell-to-cell, and long-distance movement, avoidance of host detection, counter-defense, and transmission from host to host, among other functions. Even though the multifunctionality of plant viral proteins is well documented, contemporary functional repertoires of individual proteins are incomplete. However, these can be enhanced by modeling tools. Here, predictive modeling of proteins encoded by the two genomic RNAs, i.e., RNA1 and RNA2, of grapevine fanleaf virus (GFLV) and their satellite RNAs by a suite of protein prediction software confirmed not only previously validated functions (suppressor of RNA silencing [VSR], viral genome-linked protein [VPg], protease [Pro], symptom determinant [Sd], homing protein [HP], movement protein [MP], coat protein [CP], and transmission determinant [Td]) and previously identified putative functions (helicase [Hel] and RNA-dependent RNA polymerase [Pol]), but also predicted novel functions with varying levels of confidence. These include a T3/T7-like RNA polymerase domain for protein 1A^VSR, a short-chain reductase for protein 1B^Hel/VSR, a parathyroid hormone family domain for protein 1E^Pol/Sd, overlapping domains of unknown function and an ABC transporter domain for protein 2B^MP, and DNA topoisomerase domains, transcription factor FBXO25 domain, or DNA Pol subunit cdc27 domain for the satellite RNA protein. Structural predictions for proteins 2A^HP/Sd, 2B^MP, and 3A^? had low confidence, while predictions for proteins 1A^VSR, 1B^Hel*/VSR, 1C^VPg, 1D^Pro, 1E^Pol*/Sd, and 2C^CP/Td retained higher confidence in at least one prediction. This research provided new insights into the structure and functions of GFLV proteins and their satellite protein. Future work is needed to validate these findings.