Skip to main content

Evaluation of potato virus X resistance in potato cultivars and identification of an innate immunity-independent resistance phenotype

Abstract

Potato virus X (PVX) is a widely distributed viral pathogen that causes significant losses in potato production by co-infecting with potato virus Y or potato virus A. In this study, the resistance of 23 potato cultivars to PVX was dissected in detail using a PVX infectious clone containing a yellow fluorescent protein (YFP). Among them, four potato cultivars (Longshu-3, Eugene, Atlantic and Waiyin-2) were found to carry an Rx gene that confers extreme resistance to PVX; one cultivar (Waiyin-1) displayed partial resistance and was able to delay PVX infection by ~ 5 days; while the rest eighteen potato cultivars were susceptible to PVX. Moreover, we found that the replication but not cell-to-cell or long-distance movement of PVX was inhibited in Waiyin-1. Finally, we determined that the expression of pathogenesis-related (PR) genes in Waiyin-1 was not triggered by PVX infection at early infection stage, whereas they were triggered in the Rx-carrying cultivar Atlantic during this period of time. In conclusion, our results confirm that Rx is a major type of resistance gene in potato cultivars in the Northeast part of China. Furthermore, the possible mechanism underlying Waiyin-1 resistance to PVX is discussed.

Background

Potato (Solanum tuberosum L.) is the world’s fourth most important food crop, with a global production of about 388 million tons per year according to the Food and Agriculture Organization of the United Nations (FAO) statistical databases (www.statista.com/statistics/192966/us-potato-production-since-2000). China is the largest potato producer, accounting for 26.3% of global production. Along with the transportation of seed potatoes, potato diseases, especially viral diseases are rapidly spreading across potato planting areas worldwide. At present, potato production is being seriously threatened by virus infection, which not only causes yield and quality decline but also induces seed degradation (Solomon-Blackburn and Barker 2001a). Hitherto, more than 50 viruses have been identified in potato plants (Kreuze et al. 2020a).

Potato virus X (PVX), the type species of the genus Potexvirus in the family Alphaflexiviridae, is one of the major viruses infecting potato plants worldwide (Kreuze et al. 2020b). Although it does not induce severe symptoms on most potato cultivars, coinfection of PVX with other viruses, such as potato virus A (PVA) and potato virus Y (PVY), can cause serious yield and quality losses in potato production (Kreuze et al. 2020a). For example, coinfection of PVX with potato virus A (PVA) and potato virus Y (PVY) results in crinkle symptoms and even plant death (Nie and Singh 2013). The genome of PVX consists of a positive-sense single-stranded RNA (+ ssRNA) of about 6.4 kilobase pairs (kb) in length that is encapsulated in flexuous, filamentous and non-enveloped viral particles, and encodes five open reading frames (ORFs) (Kreuze et al. 2020b). The largest ORF (ORF1) on the 5´-end of the genome encodes the viral RNA-dependent RNA polymerase (RdRp), which is absolutely required for viral replication (Betten et al. 2012). The partially overlapping ORFs [2, 3 and 4] comprise a so-called triple-gene-block (TGB) module, encoding three viral movement proteins, namely TGBp1, TGBp2 and TGBp3 (Beck et al. 1991; Tilsner et al. 2012). ORF5 encodes the viral coat protein (CP) that is involved in viral genome encapsulation and cell-to-cell movement (Cruz et al. 1998).

During a long history of coevolution with pathogens, plants have evolved sophisticated resistance mechanisms to combat the invasion of all phytopathogens including viruses (Chisholm et al. 2006). Effector-triggered immunity (ETI) is one of the main antiviral machineries, which is triggered via the recognition of pathogen effectors by intracellular nucleotide-binding domain leucine-rich repeat containing receptors (NLRs) that are historically termed resistance (R) proteins. To date, three R genes, namely Rx, Nx and Nb, have been characterized in potato, which confer resistance to PVX (Cockerham 1970; Solomon-Blackburn and Barker 2001b). The Rx gene encodes a coiled-coil NLR (CC-NLR) that specifically recognizes PVX CP and confers an extreme resistance (ER), a specific form of resistance without inducing visible local necrotic lesions (hypersensitive responses) (Bendahmane et al. 1995, 1997, 1999; Moffett et al. 2002). Nx and Nbinduce necrotic lesions on the infection sites by recognizing viral CP and TGBp1, respectively (Tommiska et al. 1998; Malcuit et al. 1999; Marano et al. 2002). In addition, several atypical dominant viral resistance proteins (ADVRPs) have been characterized. For instance, Jacalin-type lectin required potexvirus resistance 1 (JAX1) from Arabidopsis thaliana, putative methyltransferase 1 from Nicotiana benthamiana (PNbMTS1) and Remorins (REMs) from potato. Both JAX1 and PNbMTS1 interfere with virus replication by targeting viral RdRp, whereas REMs inhibit the function of TGBp1 in viral cell-to-cell movement (Cheng et al. 2009; Yamaji et al. 2012; Sugawara et al. 2013; Yoshida et al. 2019).

Identification of virus-resistant potato cultivars and dissection of their resistance mechanisms will not only facilitate sustainable potato production but also benefit potato resistance breeding. In this study, we evaluated the PVX resistance of twenty-three potato cultivars and identified a novel resistance phenotype to PVX in a potato cultivar, which will further deepen our understanding of potato resistance to PVX.

Results

Resistance of different potato cultivars to PVX

Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the tissue-culture plantlets of all 23 potato cultivars were free of PVX (Fig. 1a). These plantlets were then infiltrated with agrobacteria harboring PVX infectious clone pGR107. At 12 days post-inoculation (dpi), Kexin-18, Shepody and Netherlands-15 showed mild yellowing and/or mosaic symptoms, while other cultivars remained symptomless (Fig. 1b). Systemic leaves were analyzed by DAS-ELISA at 12 dpi. The results showed that the optical density values at 405 nm (OD405) of five cultivars, namely Longshu 3, Eugene, Atlantic, Waiyin-1 and Waiyin-2, were close to that of the negative control (healthy Zhongshu-2), whereas those of other 18 varieties were close to that of the positive control (Table 1). These data suggest that Longshu 3, Eugene, Atlantic, Waiyin-1 and Waiyin-2 are probably resistant to PVX infection. We also investigated the presence of PVX genomic RNA in the systemic leaves by RT-PCR at 15 dpi. Consistent with the DAS-ELISA results, an amplicon of the expected size of 1.5 kb was observed in all 18 ELISA-positive cultivars, whereas no band was amplified from Longshu 3, Eugene, Atlantic and Waiyin-2 (Fig. 1c). Unexpectedly, a 1.5-kb band was amplified in Waiyin-1 at 15 dpi (Fig. 1c). To further confirm the infection of PVX in Waiyin-1, we re-examined PVX genomic RNA in the systemic leaves of Waiyin-1 by RT-PCR at 9, 12 and 15 dpi. The results showed that the 1.5-kb band could only be amplified in the systemic leaves of Waiyin-1 at 15 dpi but not at 9 or 12 dpi (Fig. 1d). All amplicons were cloned and Sanger sequenced. The results confirmed that amplicons from the 18 ELISA-positive cultivars and Waiyin-1 were the genomic sequence of PVX. These results suggest that Longshu-3, Eugene, Atlantic and Waiyin-2 are fully resistant to PVX, Waiyin-1 is partial resistant to PVX, while the other 18 cultivars are susceptible to PVX.

Fig. 1
figure1

Symptoms and detection of PVX in different potato cultivars. a RT-PCR analysis of the presence of PVX in potato plantlets using primer pair pvx-tgb2-f and PVXcpRT-R. M, DL2000 DNA marker (Vazyme); P, PVX-infected Nicotiana benthamiana leaf tissues (positive control); N, healthy N. benthamiana leaf tissues (negative control). Potato cultivars were arranged in the same order as in Table 1. b PVX symptoms on plantlets of Netherlands-15 and Kexin-18 at 12 dpi. c RT-PCR analysis of the presence of PVX in the systemic leaves of potato plantlets using primers PVX5875-F and PVXcpRT-R at 15 dpi. Lanes 1, 3, 5, 7, 9 and 11 are healthy Kexin-1, Atlantic, Eugene, Waiyin-2, Longshu-3 and Waiyin-1, respectively; lanes 2, 4, 6, 8, 10 and 12 are PVX-infected Kexin-1, Atlantic, Eugene, Waiyin-2, Longshu-3 and Waiyin-1, respectively. d Detection of PVX genome in Waiyin-1 and Kexin-1 using primers PVX5875-F and PVXcpRT-R at 9, 12 and 15 dpi. H, Healthy Kexin-1; P, positive control (PVX-infected N. benthamiana leaf tissues); lanes 1, 2 and 3 are systemic leaves of Kexin-1 agroinfiltrated with pGR107 at 9, 12 and 15 dpi, respectively; lanes 4, 5 and 6 are systemic leaves of Waiyin-1 agroinfiltrated with pGR107 at 9, 12 and 15 dpi, respectively

Table 1 ELISA results of potato cultivars infected by PVX at 12 dpi

To further confirm the resistance of Waiyin-1 to PVX, we constructed a PVX infectious clone that expresses a yellow fluorescent protein (pGR107-YFP) to facilitate the direct visualization of virus infection (Fig. 2a). Infection of Nicotiana benthamiana seedlings with pGR107-YFP caused typical symptoms of PVX such as mosaic and leaf scroll-down on systemic leaves at 7 dpi (Fig. 2b, left panel). Under ultra-violet (UV) light, bright yellow fluorescence was observed on symptomatic leaves (Fig. 2b, right panel). Potato seedlings of Longshu 3, Eugene, Atlantic, Waiyin-1, Waiyin-2 and Kexin-1 were then agroinfiltrated with pGR107-YFP. It was shown that yellow fluorescence was only observed on systemic leaves of Kexin-1 at 12 dpi, which was used as a susceptible control (Fig. 2c, left panel). Interestingly, yellow fluorescence also appeared on systemic leaves of Waiyin-1 at 17 dpi (Fig. 2c, right panel), whereas no visible fluorescence signal was observed on the other 4 cultivars throughout the experimental period (data not shown). Together, these results confirm that Longshu 3, Eugene, Atlantic and Waiyin-2 are fully resistant to PVX, whereas Waiyin-1 has a partial resistance.

Fig. 2
figure2

Evaluation of the resistance of potato cultivars using a YFP-tagged PVX infection clone. a Diagram illustration of pGR107-YFP. LB and RB are left and right T-DNA border, respectively. 35S, cauliflower mosaic virus (CaMV) 35S promoter; N, NOS terminator; RdRp, RNA-dependent RNA polymerase; CP, coat protein. b Symptoms of N. benthamiana infected with pGR107-YFP under white (left panel) and UV light (right panel) at 7 dpi. c Symptoms on systemic leaves of potato plantlets infected with pGR107-YFP under white and UV light at 12 and 17 dpi. H, healthy control; I, PVX-infected treatment

Identification of the Rx gene in resistant potato cultivars

Atlantic contains the Rx gene that confers extreme resistance against PVX (Nyalugwe et al. 2012). Since no obvious necrosis was observed on the inoculated leaves of four resistant cultivars (Longshu 3, Eugene, Atlantic and Waiyin-2), we supposed that the genomes of these four cultivars also contain the Rx gene or its paralogs. A specific band of about 1.2 kb in size was successfully amplified from the genomic DNA of Longshu-3, Eugene, Atlantic or Waiyin-2 with Rx-specific primers, while no corresponding band was amplified in Kexin-1 (negative control) (Fig. 3a). Interestingly, no Rx-specific band was amplified from Waiyin-1. These results suggest that Longshu-3, Eugene, Atlantic and Waiyin-2 may contain Rx or its paralog, while Kexin-1 and Waiyin-1 don’t carry Rx. We further amplified the full-length coding region of Rx in Longshu-3, Eugene, Atlantic and Waiyin-2 by RT-PCR. The amplified fragments were then cloned and Sanger sequenced. Multiple alignment of the deduced amino acid sequences revealed that Rx of Atlantic and Longshu-3 is identical to Rx1 (GenBank accession no. AF265664); Rx of Eugene shares 96.48% and 95.31% aa identities to Rx1 and Rx2 (GenBank accession no. AJ249448), respectively; Rx in Waiyin-2 harbors a 32-aa deletion (693–724 aa) as compared to Rx1 (Fig. 3b). In the Neighbour-Joining (NJ) phylogenetic tree, all four Rx proteins cluster with Rx1 and Rx2 in the same clade (Fig. 3c). These results imply that the resistance of Longshu-3, Eugene, Atlantic and Waiyin-2 is conferred by the Rx gene, whereas there is no this gene in Waiyin-1’s genome.

Fig. 3
figure3

Analyses of the Rx gene in PVX-resistant potato cultivars. a PCR detection of the Rx gene using primer pair RxSP-S3 and RxSP-A2. M, DL2000 DNA marker (Vazyme). b Multiple sequence alignment of the amino acid sequences of Rx1, Rx2 and their paralogs from Longshu-3, Eugene, Atlantic and Waiyin-2. The conserved identical amino acids are highlighted in black. Sequences were aligned with Clustal Omega and displayed by ESPript 3.0. c Phylogenetic analysis of Rx1 and its paralogs. The phylogenetic tree was constructed using the Maximum Likelihood method with 1000 bootstrap replicates and rooted to Ry (Genbank accession no. QEL52752)

PVX infection is repressed in Waiyin-1

To understand the resistance mechanism of Waiyin-1 to PVX, we sap-inoculated Waiyin-1 and Kexin-1 plantlets with inoculum of pGR107-YFP-infected N. benthamiana leaf tissues. Fluorescent infection foci were observed in inoculated leaves of Kexin-1 under UV light at 10 dpi, while no infection spot was found in leaves of Waiyin-1 at the same time point (Fig. 4a). A time course analysis was subsequently performed to monitor PVX infection in the inoculated leaves using RT-PCR from 24 to 96 h post-inoculation (hpi). It was found that the genomic RNA of PVX in Kexin-1 showed a significant increasing trend from 48 hpi onwards, while in Waiyin-1 it just started to increase from 96 hpi onwards (Fig. 4b), suggesting that the early stage of PVX infection could be inhibited in Waiyin-1. To further confirm this hypothesis, we infiltrated Waiyin-1 and Kexin-1 leaves with agrobacteria harboring pGR107-YFP at a low concentration (an OD600 value of 0.0005), so that isolated cells became infected. The inoculated leaves were then observed with a confocal fluorescence microscope from 48 to 72 hpi at a 12-h interval. At 48 hpi, YFP-expressing cells were only observed in the inoculated leaves of Kexin-1, suggesting that PVX replication had occurred in Kexin-1 at this time point (Fig. 4c). Most fluorescent foci in Kexin-1 were expanded into more than two cells at 60 hpi, while only very faint YFP-signal was observed in isolated cells in Waiyin-1 at the same time point (Fig. 4c). At 72 hpi, cell patches with strong fluorescence were observed in Kexin-1, whereas the fluorescence in Waiyin-1 remained in isolated cells (Fig. 4c). Moreover, the fluorescence intensity in Waiyin-1 was significantly lower than that in Kexin-1 at both 60 and 72 hpi (Fig. 4d). Thus, PVX replication occurs before 48 h and starts cell-to-cell movement at about 60 hpi in Kexin-1, while the replication of PVX takes place at about 60 hpi and no cell-to-cell movement was observed even at 72 hpi in Waiyin-1.

Fig. 4
figure4

Waiyin-1 suppresses PVX infection. a Visualization of the infection foci on the leaves of Waiyin-1 and Kexin-1 plantlets sap-inoculated with pGR107-YFP at 10 dpi. Circles, mechanical injuries; triangles, the infection foci. b RT-qPCR analysis of the accumulation of viral genome RNA in Waiyin-1 and Kexin-1 infected with pGR107-YFP. Potato ACTIN 7 was used as an internal control. The genomic RNA level of pGR107-YFP in Waiyin-1 was normalized to 1. Bars represent means ± s.d. (n = 5). c Microscopic observation of the infection of Waiyin-1 and Kexin-1 by pGR107-YFP. d Quantification of fluorescence intensities in the leaves of Waiyin-1 and Kexin-1 infected with pGR107-YFP. Data represent means ± s.d. (n = 8); ** P < 0.01 (two-tailed Student’s test)

To rule out the influence of cell-to-cell movement, a movement-defective PVX infectious clone (pGR107-TGBp2∆52–60-YFP) was constructed, in which a nine-amino-acid motif (GGAYRDGTK) between the two transmembrane motifs of TGBp2 was deleted (Fig. 5a). Our previous study showed that this motif plays a critical role in PVX cell-to-cell movement (Wu et al. 2019). Three-week-old N. benthamiana seedlings were infiltrated with agrobacteria harboring pGR107-YFP or pGR107-TGBp2∆52–60-YFP. Yellow fluorescence was observed in the local leaves of these agroinfiltrated seedlings under UV light from 2 dpi onwards. The fluorescence of pGR107-TGBp2∆52–60-YFP was restricted only in the infiltration area, whereas that of pGR107-YFP spread to upper systemic leaves at 6 dpi (Fig. 5b), suggesting that pGR107-TGBp2∆52–60-YFP is defective in cell-to-cell and long-distance movement. We then sap-inoculated seedlings of Waiyin-1, Kexin-1 and Atlantic using inoculum of pGR107-TGBp2∆52–60-YFP-infected N. benthamiana leaf tissues. Kexin-1 and Atlantic were used as susceptible and resistant controls, respectively. The accumulation of PVX genomic RNA in the local inoculated leaves was evaluated by RT-qPCR at 48 and 72 hpi. It was shown that PVX genomic RNA was increased about 1.75 times from 48 to 72 hpi in Kexin-1, whereas it was decreased in Atlantic in the same time period. Interestingly, the relative level of viral genomic RNA was hardly increased in Waiyin-1 from 48 to 72 hpi (Fig. 5c). Together, these results suggest that the replication of PVX is inhibited in Waiyin-1.

Fig. 5
figure5

The replication of PVX is inhibited in Waiyin-1. a Diagram illustration of pGR107-TGBp2∆52–60-YFP. TM1 and TM2 are the transmembrane motif 1 and transmembrane motif 2 of TGBp2, respectively; other labels are the same as in Fig. 2a. b Symptoms of N. benthamiana seedlings infected with pGR107-TGBp2∆52–60-YFP under white (upper panel) and UV light (lower panel) at 6 dpi. White triangles indicate the inoculated leaves. c RT-qPCR analysis of the replication of pGR107-TGBp2∆52–60-YFP in leaves of Waiyin-1, Kexin-1 and Atlantic infected with pGR107-TGBp2∆52–60-YFP. Data represent means ± s.d. (n = 5); **P < 0.01; ns, no significant change (two-tailed Student’s test)

Innate immunity is not involved in early antiviral responses in Waiyin-1

To investigate whether the resistance of Waiyin-1 to PVX involves plant innate immunity, the expression of pathogenesis-related (PR) genes, e.g., PR1, PR2, PR3 and PR4, was evaluated during PVX infection using RT-qPCR. The expression levels of PR1, PR2, PR3 and PR4 were almost unaltered after PVX infection in Kexin-1, whereas in Atlantic, they were peaked at 48 hpi and decreased at 72 hpi (Fig. 6a–d). These results suggest that the innate immunity triggered by the Rx gene typically peaked at 48 hpi. Intriguingly, the expression of PR1 and PR4 was not changed in Waiyin-1 at 48 hpi, but significantly increased at later infection stage, e.g., 72 hpi (Fig. 6a, d), while the expression of PR2 and PR3 was gradually increased from 48 to 72 hpi in Waiyin-1(Fig. 6b, c). We further investigated the expression of WRKY1, a member of the WRKY transcription factor family involved in disease resistance, abiotic stress and some developmental processes, e.g., stomatal movement, light and nitrogen signaling pathways (Qiao et al. 2016; Heerah et al. 2019), during PVX infection. The results showed that the expression of WRKY1 was slightly increased at 48 hpi and decreased at 72 hpi in Atlantic, while no significant changes occurred in Keyin-1. Interestingly, the expression of WRKY1 was also significantly increased in Waiyin-1 at 72 hpi but not altered at 48 hpi (Fig. 6e). Together, these results suggest that although the PVX resistance in Waiyin-1 requires the expression of PR genes, it is apparently differed from the Rx-triggered innate immunity.

Fig. 6
figure6

The resistance of Waiyin-1 is associated with increased expression of PR genes. a-e The relative expression levels of PR1 (a), PR2 (b), PR3 (c), PR4 (d) and WRKY1 (e) in Waiyin-1, Kexin-1 and Atlantic at 48 and 72 hpi. Data represent means ± s.d. (n = 4); Expressions of PR1, PR2, PR3, PR4 or WRKY1 in mock-treated plants at 48 hpi (48-CK) were normalized to 1; ** P < 0.01; * P < 0.05; ns, no significant change (two-tailed Student’s test)

Discussion

In this study, we evaluated the PVX resistance of 23 potato cultivars widely cultivated in China. The results suggest that most potato varieties we tested are susceptible to PVX infection and only 4 cultivars (Longshu-3, Eugene, Atlantic and Waiyin-2) are completely resistant to PVX (Table 1 and Fig. 1c). Our results further reveal that the resistance of the 4 cultivars to PVX is conferred by the Rx gene, since the deduced amino acid sequences of Rx identified in these cultivars share high identities with Rx1 and Rx2, and all of them were clustered in the same phylogenetic branch (Fig. 3b, c). Noticeably, our bioinformatics analyses indicate that these Rx genes share considerable sequence diversity; especially, the deduced amino acid sequence of the Rx from Waiyin-2 lacks 32 aa in the LRR domain. It has been reported that mutations in the LRR domain are capable of altering the specificity of disease resistance conferred by the Rx gene (Farnham and Baulcombe 2006; Harris et al. 2013). Therefore, whether these Rx varieties have the same resistance spectrum to different PVX isolates is unknown since only the PVX UK3 isolate was evaluated in this study. Nevertheless, our results suggest that the genetic resources of PVX resistance in current potato varieties are considerably narrow, although it is believed that potato cultivars are abundant in genetic variability (Hardigan et al. 2017). As a consequence of the lack of proofreading activity in RNA-dependent RNA polymerases (RdRp), RNA viruses including PVX have a very high mutation rate (Steinhauer et al. 1992; Duffy et al. 2008), which may allow PVX to easily escape Rx-mediated resistance. Therefore, it is necessary to introduce new PVX resistance genes in future breeding projects to avoid any potential damage caused by resistance-breaking PVX isolates.

The most interesting finding in this study is the identification of a partial PVX resistance phenotype in Waiyin-1. In comparison to susceptible Kexin-1, the infection of PVX in Waiyin-1 was delayed by about 5 days. Replication and cell-to-cell movement assays showed that the replication but not movement of PVX was inhibited in Waiyin-1. Moreover, our results reveal that the expression profiles of PR genes in Waiyin-1 are apparently different from the Rx-triggered transcriptome reprogramming in which PR genes, e.g., PR1, PR2, PR3 and PR4, are upregulated at early stage of PVX infection (Knip et al. 2019). The infection of PVX in Waiyin-1 activates the expression of the four PR genes and stress-related WRKY1 at a later stage. These results suggest that the resistance of Waiyin-1 is not likely associated with a typical R protein. The resistances of most known ADVRPs, such as JAX1, REMs, PNbMTS1, h-type thioredoxin (ZmTrxh) and Tm-1, do not induce the expression of PR genes (Ishibashi et al. 2007; Cheng et al. 2009; Yamaji et al. 2012; Sugawara et al. 2013; Yoshida et al. 2019). Recently, a novel class of ADVRP that is able to confer a broad resistance to both positive- and negative-stranded RNA viruses was discovered. This class of ADVRP encodes a sulfotransferase to catalyze the conversion of salicylic acid (SA) into sulphonated SA (SSA), which serves as a signal to trigger SA biosynthesis, resulting in higher expression of PR genes (Bake et al. 2010; Wang et al. 2014; Zhao et al. 2021). Whether the resistance of Waiyin-1 is also conferred by a sulfotransferase needs to be investigated in future studies. In conclusion, our results provide new understanding on the resistance to PVX in potato plants.

Conclusions

In short, four potato cultivars (Longshu-3, Eugene, Atlantic and Waiyin-2) were found to contain the Rx gene, which confers the extreme resistance to PVX. The partial resistance of Waiyin-1 to PVX is associated with the suppression of viral replication and expression of pathogenesis-related genes. The rest eighteen potato cultivars are susceptible to PVX infection.

Methods

Virus resource, plant materials and growth condition

The infectious clone of PVX UK3 isolate (pGR107) has been described previously (Lu et al. 2003). Potato cultivars were kindly provided by Heilongjiang Academy of Agricultural Sciences. Virus-free potato seedlings were cultivated in fertile soil at 23℃, 60% humidity in a plant growth chamber with a light/dark cycle of 16 h/8 h. N. benthamiana plants were grown in pots in a plant growth chamber at 23℃ with a light/dark cycle of 16 h/8 h.

Virus inoculation

For agroinfiltration assay, Agrobacterium tumefaciens strain GV3101 harboring pSoup helper plasmid was used. PVX infectious clones were transformed by electroporation. Agrobacteria harboring proper plasmid were collected by centrifuge, washed twice with infiltration buffer (10 mM MES, pH 5.6, 10 mM MgCl2, 100 µM acetosyringone), and resuspended in infiltration buffer at room temperature. After keeping at room temperature for 1 h, agrobacteria were infiltrated into N. benthamiana or potato leaves at an optical density at 600 nm (OD600) of 0.4 or as indicated in the context using 1-mL needleless syringes.

For sap-inoculation, potato and N. benthamiana leaves were pre-dusted with 600-mesh carborundum powder, and then were rubbed with crude sap of virus-infected N. benthamiana leaves in 10 mM of sodium phosphate buffer (pH 7.0). At 2 min post-inoculation, the inoculated leaves were washed with distilled water and covered with a pre-wetted tissue napkin, and were subsequently incubated in a growth chamber at 23℃ with a light/dark cycle of 16 h/8 h for symptom development.

At least five plantlets per cultivar were agroinfiltrated or sap-inoculated. Equal amount of local or systemic leaves of five inoculated plantlets were sampled and mixed for further virus detection at indicated time.

Vector construction

To construct a yellow fluorescent protein (YFP)-tagged PVX infectious clone, the YFP coding region was amplified from pEarleyGate-101 (Earley et al. 2006) using primers 101-yfp-F (5′- ATGGTGAGCAAGGGCGAGGAGCTG-3′) and 101-yfp-sal1-R (5′- CTTGTACAGCTCGTCCATGCC-3′). The PVX infectious clone pGR107 (Lu et al. 2003) was linearized by PCR at the ClaI restriction site located downstream of the duplicated coat protein promoter using primers PVX-Cla-F (5′- GGCATGGACGAGCTGTACAAGTCGACCGCCGATGAACGGTTAAG-3′) and PVX-YFP-R (5′-CAGCTCCTCGCCCTTGCTCACCATCGATGCTAGCTGGTGCTGACCTCTTTC-3′). PVX-Cla-F and PVX-YFP-R have a 21-nt overlap with the 5′ and 3′ ends of YFP coding sequence, respectively. These two fragments were then joined together using the ClonExpress II One Step Cloning Kit (Vazyme Biotech, Nanjing, China). The movement-defective PVX infectious clone, pGR107-TGBp2∆52–60-YFP, was constructed using the same strategy with pGR107-TGBp2∆52–60 as the template (Wu et al. 2019).

Enzyme-linked immunosorbent assay (ELISA)

ELISA assay was conducted using the ELISA Reagent Set for potato virus X (Agdia, Elkhart, IN, USA) according to the provided protocol. The detailed procedure is as follows: potato leaf tissues were homogenized in general extract buffer (GEB) (0.1 g per 1 mL), and resulting leaf extracts were dispensed in capture antibodies-pretreated ELISA plates (100 µL per well). After incubating at room temperature for 2 h in a humid box, the plate was washed 7 times with 1 × PBST. Alkaline phosphatase-conjugated secondary antibody diluted in ECI buffer was then added to each well at 100 µL per well. The plate was washed 8 times with 1 × PBST after incubating at room temperature for 2 h in a humid box. Each well was added with PNP solution (1 mg/mL in PNP substrate buffer) and incubated for 60 min in the dark. Absorbance values at 405 nm were read using a Microplate reader (Thermo Scientific). All samples were repeated triply.

Nucleic acid extraction, reverse transcription (RT) and polymerase chain reaction (PCR)

Total DNA was extracted using the cetyltrimethylammonium bromide (CTAB) method (Springer 2010). Total RNA was extracted using the Eastep Super Total RNA Extraction Kit (Promega, Shanghai, China) according to the manufacturer’s instructions. First strand complimentary DNA (cDNA) was synthesized using the HiScript III 1st Strand cDNA Synthesis Kit + gDNA wiper (Vazyme) with oligo-d(T)18 and 5 µg of total RNA. PCR amplification was conducted as described previously (Liu et al. 2019). For detection, PCR reactions were performed in a 20 µL volume, consisting of 10 µL 2 × Taq Master Mix (Vazyme), 0.5 μL of RT product or total DNA, 0.5 μL of each primer (5 mmol), and 8.5 μL distilled water. The primer pair PVX5875-F (5′-GCTGGCTGTGGCTTCGATTTCGAGACCAAC-3′) and PVXcpRT-R (5′-TCTAGGCTGGCAA AGTCGTT-3′) or PVXtgb2-F (5′-GCAGGGCCATAGGCTGACCGCTCCGGTC-3′) and PVXcpRT-R were used for the detection of PVX, which can amplify a 1.5 or 1.2 kb band from the PVX genome, respectively. For identification of the Rx gene, a 1.2-kb fragment of Rx was amplified by primers RxSP-S3 (5′-ATCTTGGTTTGAATACATGG-3′) and RxSP-A2 (5′-CACAATATTGGAAGGATTCA-3′) (Ohbayashi 2019). For cloning the Rx coding sequence (CDS), PCR reactions were performed in a 50 µL volume containing 25 µL 2 × Phanta Master Mix, 0.5 μL of RT product, 1 μL of each primer (5 mmol), and 22.5 μL distilled water. Rx CDS was amplified using primers Rx-dorF (5′-GTACAAAAAAGCAGGCTTCATGGCTTATGCTGCTGTTAC-3′) and Rx-dorR (5′-CAAGAAAGCTGGGTCCCGACGCTCGACATTATTGCGGCAAG-3′) designed based on the Rx2 gene (GenBank accession no. AJ249448). PCR products were analyzed by electrophoresis using 1% agarose gels, and amplicons were purified using the FastPure Gel DNA Extraction Mini Kit (Vazyme) and then ligated into the pEASY-blunt vector (Transgen Biotech). Three independent clones of each fragment were selected for Sanger sequencing (Sangon Bio).

Quantitative PCR (qPCR) was performed in a 20 μL volume using a LightCycler 480 (Roche). The reaction mixture contains 1 μL fourfold-diluted cDNA, 1 μL (5 nM) of each primer, 10 μL 1 × AceQ® Universal SYBR qPCR Master Mix (Vazyme), and 7 μL distilled H2O. The genomic RNA level of PVX was determined using the primer set PVXcpRT-F1 (5′-GTCAGCACCAGCTAGCACAAC-3′) and PVXcpRT-R1 (5′-AGCCTCAATCTTGCTGAGGTC-3′). The expression of PR1, PR2, PR3, PR4 and WRKY1 was analyzed with primers described by Thomas et al. (2019), with potato ACTIN 7 gene (GenBank accession no. DQ252512) as an internal control. All experiments were repeated triply.

DNA sequencing and sequence analyses

DNA sequences obtained via Sanger sequencing were pretreated using the SeqBuilder program to remove the vector backbone and primer sequences and then assembled using the SeqMan program in the Lasergene 7.1 software package (DNASTAR Inc.) (Burland 2000). For multiple sequence alignment, sequences were aligned by Clustal Omega with default parameters and displayed by ESPript 3.0 (https://espript.ibcp.fr/ESPript/ESPript/index.php) (Robert and Gouet 2014; Sievers and Higgins 2018). Maximum Likelihood (ML) phylogenetic tree was constructed using the MEGA X software (Kumar et al. 2018). In detail, sequences were aligned using the Clustal W with default parameters (Chenna 2003), and then rendered for phylogeny analysis using the ML method. The node significance was evaluated with 1,000 bootstrap replicates.

Microscopic observation

Microscopic observations were performed as described previously (Wu et al. 2018). In brief, the fluorescence signal in the infiltrated leaf area was observed with a TCS SP8 LIGHTNING Confocal Microscope (Leica, Germany). YFP was excited at 496 nm and collected between 520 and 535 nm.

Availability of data and materials

Not applicable.

Abbreviations

ADVRPs:

Atypical dominant viral resistance proteins

CC-NLR:

Coiled-coil NLR

cDNA:

Complimentary DNA

CP:

Coat protein

CTAB:

Cetyltrimethylammonium bromide

dpi:

Days post-inoculation

ELISA:

Enzyme-linked immunosorbent assay

ER:

Extreme resistance

ETI:

Effector-triggered immunity

FAOSTAT:

FAO statistical databases

hpi:

Hours post-inoculation

HR:

Hypersensitive response

JAX1:

Jacalin-type lectin required for potexvirus resistance 1

kb:

Kilo-base pairs

ML:

Maximum likelihood

NJ:

Neighbor-Joining

NLRs:

Nucleotide-binding domain leucine-rich repeat containing receptors

PNbMTS1:

Putative methyltransferase 1 of Nicotiana benthamiana

ORFs:

Open reading frames

PR genes:

Pathogenesis-related genes

PVA:

Potato virus A

PVX:

Potato virus X

PVY:

Potato virus Y

qPCR:

Quantitative PCR

RdRp:

RNA-dependent RNA polymerase

REMs:

Remorins

RT-PCR:

Reverse transcription-polymerase chain reaction

SA:

Salicylic acid

SSA:

Sulphonated salicylic acid

TGB:

Triple-gene-block

YFP:

Yellow fluorescence protein

References

  1. Hardigan MA, Laimbeer FPE, Newton L, Crisovan E, Hamilton JP, Vaillancourt B, et al. Genome diversity of tuber-bearing Solanum uncovers complex evolutionary history and targets of domestication in the cultivated potato. Proc Natl Acad Sci USA. 2017;114(46):E9999-10008. https://doi.org/10.1073/pnas.1714380114.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  2. Bake D, Pathange P, Chung JS, Jiang J, Gao L, Oikawa A, et al. A stress-inducible sulphotransferase sulphonates salicylic acid and confers pathogen resistance in Arabidopsis. Plant Cell Environ. 2010;33(8):1383–92. https://doi.org/10.1111/j.1365-3040.2010.02156.x.

    CAS  Article  Google Scholar 

  3. Betten JS, Yoshinari S, Hemenway C. Potato virus X: a model system for virus replication, movement and gene expression. Mol Plant Pathol. 2013;4:125–31. https://doi.org/10.1046/j.1364-3703.2003.00156.x.

    Article  Google Scholar 

  4. Beck DL, Guilford PJ, Voot DM, Andersen MT, Forster RS. Triple gene block proteins of white clover mosaic potexvirus are required for transport. Virology. 1991;183:695–702. https://doi.org/10.1016/0042-6822(91)90998-Q.

    CAS  Article  PubMed  Google Scholar 

  5. Bendahmane A, Kanyuka K, Baulcombe DC. High-resolution genetical and physical mapping of the Rx gene for extreme resistance to potato virus X in tetraploid potato. Theor Appl Genet. 1997;95:153–62. https://doi.org/10.1007/s001220050543.

    CAS  Article  Google Scholar 

  6. Bendahmane A, Kanyuka K, Baulcombe DC. The Rx gene from potato controls separate virus resistance and cell death responses. Plant Cell. 1999;11(5):781–91. https://doi.org/10.1105/tpc.11.5.781.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  7. Bendahmane A, Köhm BA, Dedi C, Baulcombe DC. The coat protein of potato virus X is a strain-specific elicitor of Rx1-mediated virus resistance in potato. Plant J. 1995;8(6):933–41. https://doi.org/10.1046/j.1365-313X.1995.8060933.x.

    CAS  Article  PubMed  Google Scholar 

  8. Burland TG. DNASTAR's Lasergene sequence analysis software. In: Misener S, Krawetz SA, editors. Bioinformatics methods and protocols. Methods in Molecular Biology™, vol 132. Totowa, NJ: Humana Press; 2000;132: 1–91. https://doi.org/10.1385/1-59259-192-2:71

  9. Cheng CW, Hsiao YY, Wu HC, Chuang CM, Chen JS, Tsai CH, et al. Suppression of bamboo mosaic virus accumulation by a putative methyltransferase in Nicotiana benthamiana. J Virol. 2009;83(11):5796–805. https://doi.org/10.1128/JVI.02471-08.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  10. Chenna R, Sugawara H, Koike T, Lopez R, Gibson TJ, Higgins DG, et al. Multiple sequence alignment with the Clustal series of programs. Nucleic Acids Res. 2003;31(13):3497–500. https://doi.org/10.1093/nar/gkg500.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  11. Chisholm ST, Coaker G, Day B, Staskawicz BJ. Host-microbe interactions: shaping the evolution of the plant immune response. Cell. 2006;124(4):803–14. https://doi.org/10.1016/j.cell.2006.02.008.

    CAS  Article  PubMed  Google Scholar 

  12. Cockerham G. Genetical studies on resistance to potato viruses X and Y. Heredity. 1970;25:309–48. https://doi.org/10.1038/hdy.1970.35.

    Article  Google Scholar 

  13. Cruz SS, Roberts AG, Prior DAM, Chapman S, Oparka KJ. Cell-to-cell and phloem-mediated transport of potato virus X: the role of virions. Plant Cell. 1998;10(4):495–510. https://doi.org/10.1105/tpc.10.4.495.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  14. Duffy S, Shackelton LA, Holmes EC. Rates of evolutionary change in viruses: patterns and determinants. Nat Rev Genet. 2008;9:267–76. https://doi.org/10.1038/nrg2323.

    CAS  Article  PubMed  Google Scholar 

  15. Earley KW, Haag JR, Pontes O, Opper K, Juehne T, Song K, et al. Gateway-compatible vectors for plant functional genomics and proteomics. Plant J. 2006;45(4):616–29.

    CAS  Article  Google Scholar 

  16. Farnham G, Baulcombe DC. Artificial evolution extends the spectrum of viruses that are targeted by a disease-resistance gene from potato. Proc Natl Acad Sci USA. 2006;103(49):18828–33. https://doi.org/10.1073/pnas.0605777103.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  17. Harris CJ, Slootweg EJ, Goverse A, Baulcombe DC. Stepwise artificial evolution of a plant disease resistance gene. Proc Natl Acad Sci USA. 2013;110(52):21189–94. https://doi.org/10.1073/pnas.1311134110.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  18. Heerah S, Katari M, Penjor R, Coruzzi G, Marshall-Colon A. WRKY1 mediates transcriptional regulation of light and nitrogen signaling pathways. Plant Physiol. 2019;181(3):1371–88. https://doi.org/10.1104/pp.19.00685.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  19. Ishibashi K, Masuda K, Naito S, Meshi T, Ishikawa M. An inhibitor of viral RNA replication is encoded by a plant resistance gene. Proc Natl Acad Sci USA. 2007;104(34):13833–8. https://doi.org/10.1073/pnas.0703203104.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  20. Knip M, Richard MMS, Okam L, van Engelen HTD, Aalders T, Takken FLW. Activation of immune receptor Rx1 triggers distinct immune responses culminating in cell death after 4 hours. Mol Plant Pathol. 2019;20(4):575–88. https://doi.org/10.1111/mpp.12776.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  21. Kreuze JF, Souza-Dias JAC, Jeevalatha A, Figueira AR, Valkonen JPT, Jone RAC. Viral diseases in poato. In: Campos H, Ortiz O, editors. The Potato Crop: its agricultural, nutritional and social contribution to humankind. Cham: Springer; 2020a. p. 389–430. https://doi.org/10.1007/978-3-030-28683-5

  22. Kreuze JF, Vaira AM, Menzel W, Candresse T, Zavriev SK, Hammond J, et al. ICTV virus taxonomy profile: Alphaflexiviridae. J Gen Virol. 2020b;101:699–700. https://doi.org/10.1099/jgv.0.001436.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  23. Kumar S, Stecher G, Li M, Knyaz C, Tamura K. MEGA X: molecular evolutionary genetics analysis across computing platforms. Mol Biol Evol. 2018;35(6):1547–9. https://doi.org/10.1093/molbev/msy096.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  24. Liu J, Zhang L, Xu F, Chai M, Wu X, Kim U, Lv D, et al. Molecular analysis of a divergent isolate of potato virus H from potato reveals novel evolutionary feature of carlaviruses. Can J Plant Pathol. 2019;42:116–24. https://doi.org/10.1080/07060661.2019.1625947.

    CAS  Article  Google Scholar 

  25. Lu R, Malcuit I, Moffettt P, Ruiz MT, Peart J, Wu AJ, et al. High throughput virus-induced gene silencing implicates heat shock protein 90 in plant disease resistance. EMBO J. 2003;22:5690–9. https://doi.org/10.1093/emboj/cdg546.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  26. Malcuit I, Marano MR, Kavanagh TA, De Jong W, Forsyth A, Baulcombe DC. The 25-kDa movement protein of PVX elicits Nb-mediated hypersensitive cell death in potato. Mol Plant Microbe Interact. 1999;12(6):536–43. https://doi.org/10.1094/MPMI.1999.12.6.536.

    CAS  Article  Google Scholar 

  27. Marano M, Malcuit I, De Jong W, Baulcombe D. High-resolution genetic map of Nb, a gene that confers hypersensitive resistance to potato virus X in Solanum tuberosum. Theor Appl Genet. 2002;105:192–200. https://doi.org/10.1007/s00122-002-0962-9.

    CAS  Article  PubMed  Google Scholar 

  28. Moffett P, Farnham G, Peart J, Baulcombe DC. Interaction between domains of a plant NBS-LRR protein in disease resistance-related cell death. EMBO J. 2002;21(17):4511–9. https://doi.org/10.1093/emboj/cdf453.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  29. Nie X, Singh M. Response of potato, tobacco and Physalis floridana plants to mixed infection with PVX, PVYNTN and PVY° strains. Can J Plant Pathol. 2013;35(3):390–401. https://doi.org/10.1080/07060661.2013.812581.

    CAS  Article  Google Scholar 

  30. Nyalugwe EP, Wilson CR, Coutts BA, Jones RAC. Biological properties of potato virus X in potato: Effects of mixed infection with potato virus S and resistance phenotypes in cultivars from three continents. Plant Dis. 2012;96(1):43–54. https://doi.org/10.1094/PDIS-04-11-0305.

    Article  PubMed  Google Scholar 

  31. Ohbayashi K. The Rx gene derived USDA 41956 and Rx1 gene derived CPC 1673 confer equal resistance to the migration of potato virus X from potato leaves to tubers. Euphytica. 2019;215:90. https://doi.org/10.1007/s10681-019-2413-6.

    CAS  Article  Google Scholar 

  32. Qiao Z, Li CL, Zhang W. WRKY1 regulates stomatal movement in drought-stressed Arabidopsis thaliana. Plant Mol Biol. 2016;91:53–65. https://doi.org/10.1007/s11103-016-0441-3.

    CAS  Article  PubMed  Google Scholar 

  33. Robert X, Gouet P. Deciphering key features in protein structures with the new ENDscript server. Nucl Acids Res. 2014;42(W1):W320–4. https://doi.org/10.1093/nar/gku316.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  34. Sievers F, Higgins DG. Clustal Omega for making accurate alignments of many protein sequences. Protein Sci. 2018;27:135–45. https://doi.org/10.1002/pro.3290.

    CAS  Article  PubMed  Google Scholar 

  35. Solomon-Blackburn RM, Barker H. Breeding virus resistant potatoes (Solanum tuberosum): a review of traditional and molecular approaches. Heredity. 2001a;86:17–35. https://doi.org/10.1046/j.1365-2540.2001.00799.x.

    CAS  Article  PubMed  Google Scholar 

  36. Solomon-Blackburn RM, Barker H. A review of host major-gene resistance to potato viruses X, Y, A and V in potato: genes, genetics and mapped locations. Heredity. 2001b;86:8–16. https://doi.org/10.1046/j.1365-2540.2001.00798.x.

    CAS  Article  PubMed  Google Scholar 

  37. Springer NM. Isolation of plant DNA for PCR and genotyping using organic extraction and CTAB. Cold Spring Har Protoc. 2010. https://doi.org/10.1101/pdb.prot5515.

    Article  Google Scholar 

  38. Steinhauer DA, Domingo E, Holland JJ. Lack of evidence for proofreading mechanisms associated with an RNA virus polymerase. Gene. 1992;122:281–8. https://doi.org/10.1016/0378-1119(92)90216-C.

    CAS  Article  PubMed  Google Scholar 

  39. Sugawara K, Shiraishi T, Yoshida T, Fujita N, Netsu O, Yamaji Y, et al. A replicase of potato virus X acts as the resistance-breaking determinant for JAX1-mediated resistance. Mol Plant Microbe Interact. 2013;26(9):1106–12. https://doi.org/10.1094/MPMI-04-13-0094-R.

    CAS  Article  PubMed  Google Scholar 

  40. Thomas C, Mabon R, Andrivon D, Val F. The effectiveness of induced defense responses in a susceptible potato genotype depends on the growth rate of Phytophthora infestans. Mol Plant Microbe Interact. 2019;32(1):76–85. https://doi.org/10.1094/MPMI-03-18-0064-R.

    CAS  Article  PubMed  Google Scholar 

  41. Tilsner J, Linnik O, Wright KM, Bell K, Roberts AG, Lacomme C, et al. The TGB1 movement protein of Potato virus X reorganizes actin and endomembranes into the X-body, a viral replication factory. Plant Physiol. 2012;158(3):1359–70. https://doi.org/10.1104/pp.111.189605.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  42. Tommiska TJ, Hämäläinen JH, Watanabe KN, Valkonen JPT. Mapping of the gene Nxphu that controls hypersensitive resistance to potato virus X in Solanum phureja IvP35. Theor Appl Genet. 1998;96:840–3. https://doi.org/10.1007/s001220050810.

    CAS  Article  Google Scholar 

  43. Wang Q, Liu Y, He J, Zheng X, Hu J, Liu Y, et al. STV11 encodes a sulphotransferase and confers durable resistance to rice stripe virus. Nat Commun. 2014;5:4768. https://doi.org/10.1038/ncomms5768.

    CAS  Article  PubMed  Google Scholar 

  44. Wu X, Liu J, Chai M, Wang J, Li D, Wang A, et al. The potato virus X TGBp2 protein plays dual functional roles in viral replication and movement. J Virol. 2019;93(5):e01635-e1718. https://doi.org/10.1128/JVI.01635-18.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  45. Yamaji Y, Maejima K, Komatsu K, Shiraishi T, Okano Y, Himeno M, et al. Lectin-mediated resistance impairs plant virus infection at the cellular level. Plant Cell. 2012;24(2):778–93. https://doi.org/10.1105/tpc.111.093658.

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  46. Yoshida T, Shiraishi T, Hagiwara-Komoda Y, Komatsu K, Maejima K, Okano Y, et al. The plant noncanonical antiviral resistance protein JAX1 inhibits potexviral replication by targeting the viral RNA-dependent RNA polymerase. J Virol. 2019;93(3):e01506-e1518. https://doi.org/10.1128/JVI.01506-18.

    Article  PubMed  PubMed Central  Google Scholar 

  47. Zhao X, Jing Y, Luo Z, Gao S, Teng W, Zhan Y, et al. GmST1, which encodes a sulfotransferase, confers resistance to soybean mosaic virus strains G2 and G3. Plant Cell Environ. 2021. https://doi.org/10.1111/pce.14066.

    Article  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

We are grateful to Dr. Dianqiu Lv for providing potato cultivars.

Funding

This study is financially supported by the National Science Foundation of China (32022071; 31671998), the Academic Backbone Projects of Northeast Agricultural University (18XG04).

Author information

Affiliations

Authors

Contributions

XC conceived the study and wrote the manuscript. JL, YL and YF carried out the experiments. LZ and XW contributed to the materials and analysis procedure. KY analyzed data. XW revised the manuscript. All authors have read and approved the final manuscript.

Corresponding author

Correspondence to Xiaofei Cheng.

Ethics declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Liu, J., Liu, Y., Fang, Y. et al. Evaluation of potato virus X resistance in potato cultivars and identification of an innate immunity-independent resistance phenotype. Phytopathol Res 3, 21 (2021). https://doi.org/10.1186/s42483-021-00099-6

Download citation

Keywords

  • Extreme resistance
  • Potato virus X
  • Potato
  • Rx
  • Pathogenesis-related genes