A tomato bushy stunt virus-based vector for simultaneous editing and sensing to survey the host antiviral RNA silencing machinery

A tomato bushy stunt virus (TBSV)-derived vector system was applied for the delivery of CRISPR/Cas9 gene editing materials, to facilitate rapid, transient assays of host-virus interactions involved in the RNA silencing pathway. Toward this, single guide RNAs designed to target key components of the virus-induced host RNA silencing pathway (AGO2, DCL2, HEN1) were inserted into TBSV-based GFP-expressing viral vectors TBSV-GFP (TG) and its P19 defective mutant TGΔP19. This produced rapid, efficient, and specific gene editing in planta. Targeting AGO2, DCL2, or HEN1 partially rescued the lack of GFP accumulation otherwise associated with TGΔP19. Since the rescue phenotypes are normally only observed in the presence of the P19 silencing suppressor, the results support that the DCL2, HEN1, and AGO2 proteins are involved in anti-TBSV RNA silencing. Additionally, we show that knockdown of the RNA silencing machinery increases cargo expression from a nonviral binary Cas9 vector. The TBSV-based gene editing technology described in this study can be adapted for transient heterologous expression, rapid gene function screens, and molecular interaction studies in many plant species considering the wide host range of TBSV. In summary, we demonstrate that a plant virus can be used to establish gene editing while simultaneously serving as an accumulation sensor for successful targeting of its homologous antiviral silencing machinery components.

Practicing virology: making and knowing a mid-twentieth century experiment with Tobacco mosaic virus

Tobacco mosaic virus (TMV) has served as a model organism for pathbreaking work in plant pathology, virology, biochemistry and applied genetics for more than a century. We were intrigued by a photograph published in Phytopathology in 1934 showing that Tabasco pepper plants responded to TMV infection with localized necrotic lesions, followed by abscission of the inoculated leaves. This dramatic outcome of a biological response to infection observed by Francis O. Holmes, a virologist at the Rockefeller Institute for Medical Research, was used to score plants for resistance to TMV infection. Our objective was to gain a better understanding of early to mid-twentieth century ideas of genetic resistance to viruses in crop plants. We investigated Holmes' observation as a practical exercise in reworking an experiment, having been inspired by Pamela Smith's innovative Making and Knowing Project. We had a great deal of difficulty replicating Holmes' experiment, finding that biological materials and experimental customs change over time, in ways that ideas do not. Using complementary tools plus careful study and interpretation of the original text and figures, we were able to rework, yet only partially replicate, this experiment. Reading peer-reviewed manuscripts that cited Holmes' 1934 report provided an additional level of insight into the interpretation and replication of this work in the decades that followed. From this, we touch on how experimental reworking can inform our strategies to address the reproducibility "crisis" in twenty-first century science.

Expression of Separate Proteins in the Same Plant Leaves and Cells Using Two Independent Virus-Based Gene Vectors

Plant viral vectors enable the expression of proteins at high levels in a relatively short time. For many purposes (e.g., cell biological interaction studies) it may be desirable to express more than one protein in a single cell but that is often not feasible when using a single virus vector. Such a co-expression strategy requires the simultaneous delivery by two compatible and non-competitive viruses that can co-exist to each express a separate protein. Here, we report on the use of two agro-launchable coat-protein gene substitution GFP-expressing virus vector systems based on Tomato bushy stunt virus (TBSV) referred to as TG, and Tobacco mosaic virus (TMV) annotated as TRBO-G. TG expressed GFP in Nicotiana benthamiana, tomato, lettuce and cowpea, whereas expression from TRBO-G was detected only in the first two species. Upon co-infiltration of the two vectors co-expression was monitored by: molecular detection of the two slightly differently sized GFPs, suppressor-complementation assays, and using TG in combination with TRBO-RFP. All the results revealed that in N. benthamiana and tomato the TBSV and TMV vectors accumulated and expressed proteins in the same plants, the same leaves, and in the same cells. Therefore, co-expression by these two vectors provides a platform for fast and high level expression of proteins to study their cell biology or other properties.

Tobacco rattle virus (TRV)-Mediated Silencing of Nicotiana benthamiana ARGONAUTES (NbAGOs) Reveals New Antiviral Candidates and Dominant Effects of TRV-NbAGO1

The objective of this study was to determine the contribution of different ARGONAUTE proteins in Nicotiana benthamiana (NbAGOs) to the defense against silencing sensitive GFP-expressing viral constructs based on Tomato bushy stunt virus (TBSV) (Tombusvirus), Sunn-hemp mosaic virus (Tobamovirus), and Foxtail mosaic virus (Potexvirus). Upon Tobacco rattle virus (TRV)-mediated down-regulation of NbAGO1, 4, 5, or 6, no effects were noted on susceptibility to any virus construct, whereas knockdown of NbAGO2 specifically prevented silencing of P19-defective TBSV (TGdP19). Down-regulation of a new gene referred to as NbAGO5L showed some reduced silencing for TGdP19 but not for the other two virus constructs, whereas silencing of NbAGO7 gave rise to a subtle increase in susceptibility to all three viruses. Co-infiltrating different TRV-NbAGO constructs simultaneously did not enhance virus susceptibility. However, an unexpected finding was that whenever the TRV-NbAGO1 construct was present, this compromised silencing of genes targeted by co-infiltrated constructs, as shown upon co-infiltration of TRV-NbAGO1 with either TRV-NbAGO2 or TRV-Sul (targeting Magnesium chelatase I). Only after a prolonged period (approximately 2 months) did TRV-Sul-mediated systemic bleaching occur in these co-infected plants, suggesting that TRV-NbAGO1 hinders the silencing ability of other TRV-NbAGO constructs. In conclusion, this study revealed new antiviral NbAGOs and dominant effects of silencing NbAGO1.

Transgenic down-regulation of ARGONAUTE2 expression in Nicotiana benthamiana interferes with several layers of antiviral defenses

The present study aimed to analyze the contribution of Nicotiana benthamiana ARGONAUTE2 (NbAGO2) to its antiviral response against different viruses. For this purpose, dsRNA hairpin technology was used to reduce NbAGO2 expression in transgenic plants as verified with RT-PCR. This reduction was specific because the expression of other NbAGOs was not affected, and did not cause obvious developmental defects under normal growth conditions. Inoculation of transgenic plants with an otherwise silencing-sensitive GFP-expressing Tomato bushy stunt virus (TBSV) variant resulted in high GFP accumulation because antiviral silencing was compromised. These transgenic plants also exhibited accelerated spread and/or enhanced susceptibility and symptoms for TBSV mutants defective for P19 or coat protein expression, other tombusviruses, Tobacco mosaic virus, and Potato virus X; but not noticeably for Foxtail mosaic virus. These findings support the notion that NbAGO2 in N. benthamiana can contribute to antiviral defense at different levels.

Tombusvirus-based vector systems to permit over-expression of genes or that serve as sensors of antiviral RNA silencing in plants

A next generation Tomato bushy stunt virus (TBSV) coat protein gene replacement vector system is described that can be applied by either RNA inoculation or through agroinfiltration. A vector expressing GFP rapidly yields high levels of transient gene expression in inoculated leaves of various plant species, as illustrated for Nicotiana benthamiana, cowpea, tomato, pepper, and lettuce. A start-codon mutation to down-regulate the dose of the P19 silencing suppressor reduces GFP accumulation, whereas mutations that result in undetectable levels of P19 trigger rapid silencing of GFP. Compared to existing virus vectors the TBSV system has a unique combination of a very broad host range, rapid and high levels of replication and gene expression, and the ability to regulate its suppressor. These features are attractive for quick transient assays in numerous plant species for over-expression of genes of interest, or as a sensor to monitor the efficacy of antiviral RNA silencing.

Volatile compounds and antioxidative activity of Porophyllum tagetoides extracts

Porophyllum tagetoides is an annual warm-weather herb that has an intense typical smell. Its leaves are commonly used in soup preparation and traditional medicine for treatment of inflammatory diseases. Its volatile compounds and antioxidant properties were evaluated in crude, aqueous and ethanol leaf extract and an oil emulsion using different antioxidant assays in vitro, such as: DPPH radical scavenging activity, redox potential, polyphenol content, reducing power and optical density. A high antioxidative activity was found when comparing leaves with stems. The crude extract from leaves showed a very high reducing power (2.88 ± 0.20 O.D.) and DPPH radical-scavenging activity (54.63 ± 4.80%), in concordance with a major concentration of vitamin C (23.97 ± 0.36 mg/100 g). Instead, the highest polyphenol content (264.54 ± 2.17 mg GAE/g of sample) and redox potential (561.23 ± 0.15 mV) were found by the ethanol and aqueous extract, respectively. Aldehydes and terpenes such as nonanal, decanal, trans-pineno, β-myrcene and D-limonene were the major volatiles found. This study suggests that Porophyllum tagetoides extracts could be used as antioxidants.

Factors associated with premature chromosome condensation (PCC) following in vitro fertilization

From January 1989 to July 1990 a total of 562 oocytes was fixed in our In Vitro Fertilization Program, while cytogenetic data were collected in the case of 433. Forty-eight of these (11%) had a set of oocyte chromosomes in metaphase II, and at least one other set of sperm chromosomes prematurely condensed in the form of single chromatids. In the literature this phenomenon, frequent in our experience, has not been separately studied by many authors. Comparative studies with diverse parameters have shown a significant correlation between the same phenomenon and the use of follicle-stimulating hormone supplementation in ovarian stimulation protocols. Also, in some cases we found a high percentage of repetition of the phenomenon in one patient.

Selegiline use to prevent progression of Parkinson's disease. Experience in 22 de novo patients

To test the hypothesis that selegiline (L-deprenyl), a selective inhibitor of B-type monoamine oxidase, can halt the natural progression of Parkinson's disease, its use in 22 naive patients (mean age, 58 years; mean Parkinson's disease duration, 2.3 years) in the early stages (1 to 2) of the disease was studied. Patients were started and maintained on a daily dose of 10 mg of selegiline, and they underwent neurologic examinations at 3-month intervals using our center's disease staging and total rated disability scores. The criterion set for disease progression was defined as either the appearance of a new objective sign and/or a definite, persistent worsening (greater than 25%) of existing signs after the initiation of the selegiline trial. Patients remained on a regimen of selegiline [corrected] for periods ranging from 7 to 84 months. At the time of their latest neurologic examination, 17 (77%) of the 22 patients had conditions that demonstrably worsened with selegiline alone at an average of 10.8 months from the start of the drug therapy. Six of these 17 patients with worsening conditions (or 27% of the original 22) eventually required the addition of levodopa with carbidopa (Sinemet) on average at 13 months from the start of selegiline therapy; they have continued, to date, taking this combination for an additional mean follow-up period of 20.7 months. Four of the original 22 patients had relatively unchanged, stable neurologic status at the time of their latest examination (average follow-up period, 11.6 months).(ABSTRACT TRUNCATED AT 250 WORDS)

Selegiline as an adjunct to conventional levodopa therapy in Parkinson's disease. Experience with this type B monoamine oxidase inhibitor in 200 patients

Two hundred patients at a median age of 63 years, receiving conventional levodopa therapy for 8 years, who had had Parkinson's disease for 10 years, tried a regimen of selegiline (L-deprenyl), a type B monoamine oxidase inhibitor, at a daily dose of 10 mg, for varying periods from less than 6 months to more than 24 months (28% over 24 months). Selegiline does improve parkinsonism during the initial 6 months to 12 to 24 months of combined therapy in one third to almost half of patients with an end-of-dose type of response to long-term levodopa therapy. However, even this particular class of patients is unable to maintain such an improvement by 36 months, much less by 48 months, from the start of the selegiline trial. About one quarter of poor responders to levodopa and those with random deterioration show improvement in their parkinsonian status in the first 6 months of the selegiline trial, but their conditions quickly deteriorate by 1 year. The predominant pattern of response to previous levodopa therapy and the severity of the total disability score at the initiation of the selegiline trial were the two variables that were predictive of risk of failure with the drug. No evidence suggested that selegiline decreases the excess mortality rate of Parkinson's disease above that achieved with the use of levodopa alone. Selegiline as an adjunctive agent to conventional levodopa therapy was not unduly impressive with regard to preventing progression of Parkinson's disease.

Treatment of Parkinson's disease in early and late phases. Use of pharmacological agents with special reference to deprenyl (selegiline)

There are at present numerous pharmacological agents available for the control of parkinson symptoms. None are ideal; all have their limitations. The most potent is levodopa administered with a peripheral decarboxylase inhibitor. However, because its effectiveness declines after long-term use and side effects increase in severity, it should be reserved for individuals with established symptoms which are functionally impairing. In patients with minimal symptoms, anticholinergic agents, or agents which facilitate dopaminergic mechanisms normally operative in the nervous system, should be used. In a limited trial, deprenyl has produced promising results during this phase of parkinsonism. Deprenyl's major usefulness however, has been demonstrated in patients under treatment with levodopa which has become complicated by fluctuating responses--particularly those of the end-start-dose variety. In such patients, it is possible to achieve an increase in "on" time and a decrease in the severity of parkinsonism. In most patients, such a response can maintained for a period of two years or longer.

Organic mental syndrome and confusional states in Parkinson's disease. Relationship to computerized tomographic signs of cerebral atrophy

Ninety-three patients with a diagnosis of Parkinson's disease, otherwise unselected, were specifically evaluated for organic mental syndrome (OMS) and other neurologic motor signs other than those referrable to extrapyramidal dysfunction; in addition, they had cranial computerized tomography (CT) to measure any structural changes in brain parenchyma. Cortical (sulci) atrophy and ventricular enlargement as CT signs of cerebral atrophy were correlated with different clinical patterns of the disease. An age-adjusted control population, with intact mentation, was similarly studied. The presence of classic OMS in a sizable segment of the usual parkinsonian population was invariably associated with CT signs of cerebral atrophy. Atrophic changes on CT scans, however, were not necessarily correlated with any intellectual dysfunction, or only weakly so, independent of age. The "typical" parkinsonian patients without evidence of OMS were indistinguishable from an age-adjusted control group with regard to structural changes in their scans. However, the parkinsonian patients with definite, permanent OMS and other focal neurologic deficit probably constitute a separate or distinct subset of the parkinsonian population, with a pathologic substrate more likely to be similar to that of the so-called Alzheimer-type dementias. Duration of the parkinsonian syndrome was not predictive of either mental status or scan findings, after adjustment for age as a factor.