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Foreground and background selections are two important aspects that need to be carefully considered by plant breeders during field selection. In this article, we used 7 disease resistance markers, including four late blight and three potato virus disease resistance gene markers, and 12 microsatellite markers to evaluate the disease resistance and genetic diversity of 76 potato cultivars in total which were collected from 15 provinces of China. The foreground selection results showed that a number of materials, clustered separately, contained more than two late blight resistance markers or pyramided late blight and virus disease resistance gene markers together. A lot of them were collected from the southwest of China. Additionally, the genetic backgrounds of all cultivars were relatively narrow and a limited number of cultivars (15.8%) contained both potato late blight and potato virus Y resistance markers. Also, only two accessions (Yunshu 103 and Lishu 7) contained both late blight and potato virus X resistance markers. In conclusion, this comprehensive evaluation of genetic resources will shed the light on potato disease resistance breeding in the future.

• RNA silencing functions as an anti-viral defence in plants through the action of DICER-like (DCL) and ARGONAUTE (AGO) proteins. Despite the importance of this mechanism, little is known about the functional consequences of variation in genes encoding RNA silencing components. • The AGO2 protein has been shown to be important for defense against multiple viruses, and we investigated how naturally occurring differences in AGO2 between and within species affects its antiviral activities. • We find that the AGO2 protein from Arabidopsis thaliana, but not Nicotiana benthamiana, effectively limits potato virus X (PVX). Consistent with this, we find that the A. thaliana AGO2 gene shows a high incidence of polymorphisms between accessions, with evidence of selective pressure. Using functional analyses, we identify polymorphisms that specifically affect AGO2 antiviral activity, without interfering with other AGO2-associated functions such as anti-bacterial resistance or DNA methylation. • Our results suggest that viruses adapt to overcome RNA silencing in their hosts. Furthermore, they indicate that plant–virus interactions have influenced natural variation in RNA-silencing components and that the latter may be a source of genetically encoded virus resistance.

Background Plant viruses cause severe economic losses in agricultural production. An ultrahigh activity plant immune inducer (i.e., ZhiNengCong, ZNC) was extracted from endophytic fungi, and it could promote plant growth and enhance resistance to bacteria. However, the antiviral function has not been studied. Our study aims to evaluate the antiviral molecular mechanisms of ZNC in tobacco. Results Here, we used Potato X virus (PVX), wild - type tobacco and NahG transgenic tobacco as materials to study the resistance of ZNC to virus. ZNC exhibited a high activity in enhancing resistance to viruses and showed optimal use concentration at 100–150 ng/mL. ZNC also induced reactive oxygen species accumulation, increased salicylic acid (SA) content by upregulating the expression of phenylalanine ammonia lyase (PAL) gene and activated SA signaling pathway. We generated transcriptome profiles from ZNC-treated seedlings using RNA sequencing. The first GO term in biological process was positive regulation of post-transcriptional gene silencing, and the subsequent results showed that ZNC promoted RNA silencing. ZNC-sprayed wild-type leaves showed decreased infection areas, whereas ZNC failed to induce a protective effect against PVX in NahG leaves. Conclusion All results indicate that ZNC is an ultrahigh-activity immune inducer, and it could enhance tobacco resistance to PVX at low concentration by positively regulating the RNA silencing via SA pathway. The antiviral mechanism of ZNC was first revealed in this study, and this study provides a new antiviral bioagent.

The potato (Solanum tuberosum) nucleotide binding-leucine-rich repeat immune receptor Rx confers resistance to Potato virus X (PVX) and requires Ran GTPase-activating protein 2 (RanGAP2) for effective immune signaling. Although Rx does not contain a discernible nuclear localization signal, the protein localizes to both the cytoplasm and nucleus in Nicotiana benthamiana. Transient coexpression of Rx and cytoplasmically localized RanGAP2 sequesters Rx in the cytoplasm. This relocation of the immune receptor appeared to be mediated by the physical interaction between Rx and RanGAP2 and was independent of the concomitant increased GAP activity. Coexpression with RanGAP2 also potentiates Rx-mediated immune signaling, leading to a hypersensitive response (HR) and enhanced resistance to PVX. Besides sequestration, RanGAP2 also stabilizes Rx, a process that likely contributes to enhanced defense signaling. Strikingly, coexpression of Rx with the Rx-interacting WPP domain of RanGAP2 fused to a nuclear localization signal leads to hyperaccumulation of both the WPP domain and Rx in the nucleus. As a consequence, both Rx-mediated resistance to PVX and the HR induced by auto-active Rx mutants are significantly suppressed. These data show that a balanced nucleocytoplasmic partitioning of Rx is required for proper regulation of defense signaling. Furthermore, our data indicate that RanGAP2 regulates this partitioning by serving as a cytoplasmic retention factor for Rx.

Plant growth-promoting rhizobacteria such as Azospirillum brasilense Sp7 can protect plants against viruses but the molecular basis of this phenomenon is unclear. We therefore used differential proteomics to study two pathosystems in the presence and absence of Sp7 during early vegetative growth: tomato (Solanum lycopersicum L. cv. Boludo)/Potato virus X (PVX, KJ631111)/Sp7, and maize (Zea mays cv. B73)/Maize dwarf mosaic virus (MDMV, AM110558)/Sp7). In the maize/MDMV system, PDQuest revealed significant variations in the levels of 19 proteins compared to uninfected controls, including the upregulation of NADP-dependent malic enzyme as a form of host-specific viral anticipation, causing a simultaneous increase in the abundance of proteins related to photosynthesis and plastid functions. However, 42 proteins varied significantly in the maize/MDMV/Sp7 system, including the upregulation of radical-scavenging enzymes and proteins related to methionine metabolism, the glutathione-ascorbate cycle and photosynthesis, increasing the photosynthetic rate. In the tomato/PVX system, we observed significant variations in the levels of 58 proteins reflecting the disruption of the Calvin-Benson cycle, responses to oxidative stress and the inhibition of photosystem II (PSII) activity. We identified 26 proteins that varied in the tomato/PVX/Sp7 system; PSII and plastid proteins transiently declined but partially recovered over time as the Calvin-Benson cycle was induced to compensate. Sp7 therefore triggers induced systemic resistance in both pathosystems without affecting the virus titer, although it does delay the appearance of MDMV. The role of ribulose-1.5-bisphosphate carboxylase/oxygenase small subunit as a host target for viruses is discussed in both pathosystems.

Salicylic acid (SA) is an inducer of systemic acquired resistance (SAR) and could be a potential candidate in the control of plant virus diseases. In this study we assayed under controlled conditions the potential effect of three doses of exogenous SA treatment on tomato plants infected with Potato virus X (PVX) and measured their effects on: different physiological parameters (gas exchange, stable isotopes, chlorophyll content), the activation of secondary metabolism, viral accumulation and induction of the expression of pathogenesis-related proteins (PRs) such as ß-1, 3-glucanase (PR2) and chitinase (PR3). SA treatment increased the expression of PR2, the activity of phenylalanine ammonia lyase (PAL) and the concentration of antioxidant compounds at 7 days post-treatment. Earlier expression of PR3 compared to PR2 was observed. SA treatment delayed the detection of PVX by ELISA in uninoculated leaves of mechanically infected tomato plants. Although the effect of PVX infection on physiological parameters was weak, moderate SA treatments showed enhanced photosynthesis, particularly for infected plants. The results obtained confirm that SA promotes major changes in the induction of resistance in tomato plants and suggest that treatment with exogenous SA could be considered to reduce the infections caused by PVX.

Plant molecular farming has a great potential to produce valuable proteins. Transient expression technology provides high yields of recombinant proteins in greenhouse-grown plants, but every plant must be artificially agroinfiltrated, and open greenhouse systems are less controlled. Here, we propose to propagate agrobacteria-free plants with high-efficient long-term self-replicated transient gene expression in a well-controlled closed in vitro system. Nicotiana benthamiana plant tissue culture in vitro, with transient expression of recombinant GFP, was obtained through shoot induction from leaf explants infected by a PVX-based vector. The transient expression occurs in new tissues and regenerants due to the natural systemic distribution of viral RNA carrying the target gene. Gene silencing was delayed in plants grown in vitro, and GFP was detected in plants for five to six months. Agrobacteria-free, GFP-expressing plants can be micropropagated in vitro (avoiding an agroinfiltration step), “rejuvenated” through regeneration (maintaining culture for years), or transferred in soil. The mean GFP in the regenerants was 18% of the total soluble proteins (TSP) (0.52 mg/g of fresh leaf weight (FW). The highest value reached 47% TSP (2 mg/g FW). This study proposes a new method for recombinant protein production combining the advantages of transient expression technology and closed cultural systems.

• Plant viruses encode movement proteins (MPs) that ensure the transport of viral genomes through plasmodesmata (PD) and use cell endomembranes, mostly the endoplasmic reticulum (ER), for delivery of viral genomes to PD and formation of PD-anchored virus replication compartments. • Here, we demonstrate that the Hibiscus green spot virus BMB2 MP, an integral ER protein, induces constrictions of ER tubules, decreases the mobility of ER luminal content, and exhibits an affinity to highly curved membranes. These properties are similar to those described for reticulons, cellular proteins that induce membrane curvature to shape the ER tubules. Similar to reticulons, BMB2 adopts a W-like topology within the ER membrane. • BMB2 targets PD and increases their size exclusion limit, and these BMB2 activities correlate with the ability to induce constrictions of ER tubules. We propose that the induction of ER constrictions contributes to the BMB2-dependent increase in PD permeability and formation of the PD-associated replication compartments, therefore facilitating the virus intercellular spread. • Furthermore, we show that the ER tubule constrictions also occur in cells expressing TGB2, one of the three MPs of Potato virus X (PVX), and in PVX-infected cells, suggesting that reticulon- like MPs are employed by diverse RNA viruses.

Background It is believed that viruses affect potato yield more than any other pathogens worldwide. Method and Results We report here on a survey of the four most common potato viruses in the Tokat Province of northern Turkey. Leaf samples were collected from potato plants showing signs of viral diseases in five districts of the province. Over 400 leaf samples were tested using RT-PCR with virus-specific primers. Among the one or more viruses detected in 218 (52%) leaf samples, Potato virus Y (PVY) was the most common (47.1%), followed by potato virus S (PVS; 16.7%), potato virus X (PVX; 6.0%) and potato leaf roll virus (PLRV; 5.3%). The most common mixed infections were PVY + PVS (6.9%). A phylogenetic analysis of the gene sequences showed all Turkish PVS isolates to be clustered with the PVS O group, two PVY isolates with the PVY N−WI group and one isolate with the PVY NTN group. Turkish PVX isolates are in the Type X group of the two major PVX isolate groups. The Turkish PLRV isolates were separated into two major groups depending on the results of the phylogenetic analysis, with six cases in Group 1 and one in Group 2. Conclusions PVY, PVX, PVS and PLRV were detected in potato production areas in Tokat. A phylogenetic comparison of the gene sequences revealed all Turkish isolates to be immigrant members of the world populations of these viruses. Our results emphasize the importance of the strict quarantine control of plant materials entering Turkey.

Taxonomy Potato virus X is the type‐member of the plant‐infecting Potexvirus genus in the family Alphaflexiviridae. Physical properties Potato virus X (PVX) virions are flexuous filaments 460–480 nm in length. Virions are 13 nm in diameter and have a helical pitch of 3.4 nm. The genome is approximately 6.4 kb with a 5′ cap and 3′ poly(A) terminus. PVX contains five open reading frames, four of which are essential for cell‐to‐cell and systemic movement. One protein encodes the viral replicase. Cellular inclusions, known as X‐bodies, occur near the nucleus of virus‐infected cells. Hosts The primary host is potato, but it infects a wide range of dicots. Diagnostic hosts include Datura stramonium and Nicotiana tabacum. PVX is transmitted in nature by mechanical contact. Useful website https://talk.ictvonline.org/ictv‐reports/ictv_online_report/positive‐sense‐rna‐viruses/w/alphaflexiviridae/1330/genus‐potexvirus Potato virus X, one of the oldest known and well‐studied plant viruses, has contributed much to our current knowledge of plant immunity in potato and tobacco, and is a versatile vector for expressing foreign genes in plants.