Increased Diversity of Citrus Tristeza Virus in Europe.

This study investigated the genetic diversity of citrus tristeza virus (CTV) isolates from Montenegro and Croatia, European countries with the northernmost citrus growing regions situated on the Eastern Adriatic coast. Fifteen complete or nearly complete CTV genomes were reconstructed from high-throughput sequencing of samples collected in distinct municipalities in Montenegro and Opuzen municipality in Croatia. Phylogenetic analyses assigned some of the sequences to VT and T30 strains, previously recorded in Europe, while remarkably other isolates were placed in S1 and RB groups, which have not been reported in Europe so far. In addition, a new phylogenetic lineage including only isolates from Montenegro was delineated and tentatively proposed as the MNE cluster. Recombination analysis revealed evidence of 11 recombination events in the sequences obtained in this study, between isolates of related strains, within isolates of the same strain, and between distant strains. These findings show that CTV diversity in Europe is higher than reported before and calls for the re-evaluation of management strategies.

Root Resorptions on Adjacent Teeth Associated with Impacted Maxillary Canines.

AIM: Through the use of CBCT images, many unidentified features of impacted canines can be easily resolved. The potential collision of impacted maxillary canines and adjacent teeth could lead to root resorption (RR). The aim of this study is to examine the prevalence, location and severity of RR on adjacent teeth caused by impacted maxillary canines and the association between the adjacent teeth and the features of maxillary impacted canines on CBCT. METHODS: This study examined 89 subjects with 108 maxillary impacted canines, having had no previous orthodontic treatment (mean age: 18.3 ± 4.1 years). The following impacted-canine-related parameters were analyzed on the CBCT images: location; RR levels on adjacent teeth; occlusal line and midline distances of impacted canines; and the angulations of impacted canines to the midline, lateral incisor and occlusal line. Logistic regression was used to evaluate the association between RR and the measured parameters on CBCT. RESULTS: In this study, we found that the majority of our patients with impacted maxillary canines were female (62.5%). Of the total 108 maxillary impacted canines, 60.2% resorbed the adjacent teeth of the affected quadrants. Lateral incisors were the most affected (34.3%). The mean age of subjects with RR was 16.7 ± 3.5 years. The frequency of RR was statistically significantly higher in female subjects (40.4%). Slight RR was the most frequent (30.5%) and the highest incidence noted at the apical third of the root (29.6%). Regarding the impacted maxillary canine angulation to the midline and adjacent tooth, higher values of angulation caused severe forms of RR (p < 0.05). CONCLUSION: The sensitivity of CBCT allows for the accurate diagnosis of the location and the degree of RR, alongside the angulation and distance of impacted canines to adjacent teeth. The association between the linear and angular features of the impacted maxillary canines and RR was confirmed.

The apparent non-host resistance of Ethiopian mustard to a radish-infecting strain of Turnip mosaic virus is largely determined by the C-terminal region of the P3 viral protein.

Two different isolates of Turnip mosaic virus (TuMV: UK 1 and JPN 1) belonging to different virus strains were tested on three different Brassica species, namely turnip (Brassica rapa L.), Indian mustard (Brassica juncea L.) and Ethiopian mustard (Brassica carinata A. Braun). Although all three hosts were readily infected by isolate UK 1, isolate JPN 1 was able to establish a visible systemic infection only in the first two. Ethiopian mustard plants showed no local or systemic symptoms, and no virus antigens could be detected by enzyme-linked immunosorbent assay (ELISA). Thus, this species looks like a non-host for JPN 1, an apparent situation of non-host resistance (NHR). Through an experimental approach involving chimeric viruses made by gene interchange between two infectious clones of both virus isolates, the genomic region encoding the C-terminal domain of viral protein P3 was found to bear the resistance determinant, excluding any involvement of the viral fusion proteins P3N-PIPO and P3N-ALT in the resistance. A further determinant refinement identified two adjacent positions (1099 and 1100 of the viral polyprotein) as the main determinants of resistance. Green fluorescent protein (GFP)-tagged viruses showed that the resistance of Ethiopian mustard to isolate JPN 1 is only apparent, as virus-induced fluorescence could be found in discrete areas of both inoculated and non-inoculated leaves. In comparison with other plant-virus combinations of extreme resistance, we propose that Ethiopian mustard shows an apparent NHR to TuMV JPN 1, but not complete immunity or extreme resistance.

Biological relevance of a stable biochemical interaction between the tombusvirus-encoded P19 and short interfering RNAs.

The Tomato bushy stunt virus (TBSV)-encoded p19 protein (P19) is widely used as a robust tool to suppress RNA interference (RNAi) in various model organisms. P19 dimers appropriate 21-nucleotide (nt) duplex short interfering RNAs (siRNAs) generated by Dicer presumably to prevent programming of the RNA-induced silencing complex (RISC). In the context of virus infection, this model predicts that P19 mutants compromised for siRNA binding cannot prevent RISC-mediated degradation of TBSV RNA and thus reduce viral pathogenicity. To test this, we used P19/43 (R-->W), which is less pathogenic than wild-type P19 (wtP19), and P19/75-78 (RR-->GG), with pathogenicity properties (i.e., viral spread and symptom induction) comparable to those of a P19-null mutant. We demonstrate that P19/43 still suppresses RNAi-mediated viral RNA degradation in infected Nicotiana benthamiana, while P19/75-78 is unable to prevent this clearance of viral RNA, leading to an irreversible recovery phenotype. Gel filtration and immunoprecipitation assays show that at the onset of the infection, wtP19, P19/43, and P19/75-78 readily accumulate, and they form dimers. The wtP19 is stably associated with duplex approximately 21-nt TBSV siRNAs, while P19/75-78 does not bind these molecules, and the electrostatic interaction of P19/43 with siRNAs is perturbed for approximately 21-nt duplexes but not for longer siRNAs. This is the first clear demonstration of a direct correlation between a novel structurally orchestrated siRNA binding of an RNAi suppressor and its roles in viral pathogenesis. The findings should be particularly valuable for the RNAi field in general because the P19 mutants enable precise determination of siRNA appropriation effects.