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The Complexity of the Potyviral Interaction Network

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A special issue of Viruses (ISSN 1999-4915). This special issue belongs to the section "Viruses of Plants, Fungi and Protozoa".

Deadline for manuscript submissions: closed (30 November 2019) | Viewed by 61122

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Special Issue Editors

Dr. Kristiina Mäkinen

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Guest Editor

Department of Agricultural Sciences, Faculty of Agriculture and Forestry, University of Helsinki, 00014 Helsinki, Finland
Interests: potyviruses; molecular virus-host interactions; viral replication; viral silencing suppression; viral translation; encapsidation
Special Issues, Collections and Topics in MDPI journals

Dr. Sylvie German-Retana

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Guest Editor

UMR BFP 1332 (Biologie du Fruit et Pathologie), Equipe de Virologie, Centre INRA de Bordeaux, CS 20032, 33882, CEDEX, Villenave d’Ornon, France
Interests: plant virology, potyviruses, recessive resistance, movement

Special Issue Information

Dear Colleagues,

Many potyvirus species belong to the most economically significant plant viruses and they cause substantial yield losses to crop plants globally. Due to their efficient spread by aphids, potyviruses are difficult to control. The study of infection biology and host–potyvirus interactions is therefore essential for the development of anti-viral strategies and resistant cultivars.

Potyvirus research is advancing fast in various sectors. Our increasing knowledge about the complex molecular relationships that potyviruses have with their hosts—with the host plant organelles, cell membrane networks, metabolic pathways, and various cellular processes—is building a fascinating picture of the potyviral infection cycle. The eleven multifunctional viral proteins, responsible for orchestrating the potyviral life cycle, are participating in dozens of interactions within the host cells. Regulation of these interactions, which may be pro- or antiviral in nature, is achieved by sequestering the infection stages to various subcellular compartments and by posttranslational modifications of the viral and host proteins.

We invite contributions to enlighten the current state of the art in potyvirus research and to highlight the valuable work carried out in different laboratories throughout the world to combat the severe plant diseases caused by the members of the potyvirus group.

Dr. Kristiina Mäkinen
Dr. Sylvie German-Retana
Guest Editors

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Keywords

potyvirus infection
potyvirus–host interactions
potyviral replication and translation
intra- and intercellular potyviral movement
potyvirus transmission
host defense against potyvirus infection
potyvirus resistance

Published Papers (14 papers)

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Editorial

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2 pages, 163 KiB

Open AccessEditorial

Special Issue: “The Complexity of the Potyviral Interaction Network”

by Sylvie German-Retana and Kristiina Mäkinen

Viruses 2020, 12(8), 874; https://0-doi-org.brum.beds.ac.uk/10.3390/v12080874 - 11 Aug 2020

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Abstract

Many potyvirus species are among the most economically-significant plant viruses as they cause substantial yield losses to crop plants globally [...] Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

Research

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19 pages, 2533 KiB

Open AccessArticle

Common and Strain-Specific Post-Translational Modifications of the Potyvirus Plum pox virus Coat Protein in Different Hosts

by Marta Hervás, Sergio Ciordia, Rosana Navajas, Juan Antonio García and Sandra Martínez-Turiño

Viruses 2020, 12(3), 308; https://0-doi-org.brum.beds.ac.uk/10.3390/v12030308 - 12 Mar 2020

Cited by 5 | Viewed by 2598

Abstract

Phosphorylation and O-GlcNAcylation are widespread post-translational modifications (PTMs), often sharing protein targets. Numerous studies have reported the phosphorylation of plant viral proteins. In plants, research on O-GlcNAcylation lags behind that of other eukaryotes, and information about O-GlcNAcylated plant viral proteins is extremely scarce. The potyvirus Plum pox virus (PPV) causes sharka disease in Prunus trees and also infects a wide range of experimental hosts. Capsid protein (CP) from virions of PPV-R isolate purified from herbaceous plants can be extensively modified by O-GlcNAcylation and phosphorylation. In this study, a combination of proteomics and biochemical approaches was employed to broaden knowledge of PPV CP PTMs. CP proved to be modified regardless of whether or not it was assembled into mature particles. PTMs of CP occurred in the natural host Prunus persica, similarly to what happens in herbaceous plants. Additionally, we observed that O-GlcNAcylation and phosphorylation were general features of different PPV strains, suggesting that these modifications contribute to general strategies deployed during plant-virus interactions. Interestingly, phosphorylation at a casein kinase II motif conserved among potyviral CPs exhibited strain specificity in PPV; however, it did not display the critical role attributed to the same modification in the CP of another potyvirus, Potato virus A. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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14 pages, 2455 KiB

Open AccessArticle

Differential Accumulation of Innate- and Adaptive-Immune-Response-Derived Transcripts during Antagonism between Papaya Ringspot Virus and Papaya Mosaic Virus

by Pablo Vargas-Mejía, Julio Vega-Arreguín, Gabriela Chávez-Calvillo, Enrique Ibarra-Laclette and Laura Silva-Rosales

Viruses 2020, 12(2), 230; https://0-doi-org.brum.beds.ac.uk/10.3390/v12020230 - 19 Feb 2020

Cited by 6 | Viewed by 5453

Abstract

Papaya ringspot virus (PRSV), a common potyvirus infecting papaya plants worldwide, can lead to either antagonism or synergism in mixed infections with Papaya mosaic virus (PapMV), a potexvirus. These two unrelated viruses produce antagonism or synergism depending on their order of infection in the plant. When PRSV is inoculated first or at the same time as PapMV, the viral interaction is synergistic. However, an antagonistic response is observed when PapMV is inoculated before PRSV. In the antagonistic condition, PRSV is deterred from the plant and its drastic effects are overcome. Here, we examine differences in gene expression by high-throughput RNA sequencing, focused on immune system pathways. We present the transcriptomic expression of single and mixed inoculations of PRSV and PapMV leading to synergism and antagonism. Upregulation of dominant and hormone-mediated resistance transcripts suggests that the innate immune system participates in synergism. In antagonism, in addition to innate immunity, upregulation of RNA interference-mediated resistance transcripts suggests that adaptive immunity is involved. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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22 pages, 4424 KiB

Open AccessArticle

Insights into the Functions of eIF4E-Binding Motif of VPg in Potato Virus A Infection

by Shreya Saha and Kristiina Mäkinen

Viruses 2020, 12(2), 197; https://0-doi-org.brum.beds.ac.uk/10.3390/v12020197 - 11 Feb 2020

Cited by 22 | Viewed by 3434

Abstract

The interaction between the viral protein genome-linked (VPg) and eukaryotic initiation factor 4E (eIF4E) or eIF(iso)4E of the host plays a crucial role in potyvirus infection. The VPg of potato virus A (PVA) contains the Tyr-X-X-X-X-Leu-phi (YXXXLΦ) binding motif for eIF(iso)4E. In order to investigate its role in PVA infection, we substituted the conserved tyrosine and leucine residues of the motif with alanine residues in the infectious cDNA of PVA (PVA^VPgmut). PVA^VPgmut RNA replicated in infiltrated leaves, but RNA accumulation remained low. Systemic infection occurred only if a reversion to wild type PVA occurred. VPg was able to stabilize PVA RNA and enhance the expression of Renilla luciferase (3’RLUC) from the 3’ end of the PVA genome. VPg^mut could not support either PVA RNA stabilization or enhanced 3’RLUC expression. The RNA silencing suppressor helper-component proteinase (HCPro) is responsible for the formation of PVA-induced RNA granules (PGs) during infection. While VPg^mut increased the number of PG-like foci, the percentage of PVA RNA co-localization with PGs was reduced from 86% to 20%. A testable hypothesis for future studies based on these results is that the binding of eIF(iso)4E to PVA VPg via the YXXXLΦ motif is required for PVA RNA stabilization, as well as the transfer to the RNA silencing suppression pathway and, further, to polysomes for viral protein synthesis. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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14 pages, 636 KiB

Open AccessArticle

Host Range Evolution of Potyviruses: A Global Phylogenetic Analysis

by Benoît Moury and Cécile Desbiez

Viruses 2020, 12(1), 111; https://0-doi-org.brum.beds.ac.uk/10.3390/v12010111 - 16 Jan 2020

Cited by 32 | Viewed by 5009

Abstract

Virus host range, i.e., the number and diversity of host species of viruses, is an important determinant of disease emergence and of the efficiency of disease control strategies. However, for plant viruses, little is known about the genetic or ecological factors involved in the evolution of host range. Using available genome sequences and host range data, we performed a phylogenetic analysis of host range evolution in the genus Potyvirus, a large group of plant RNA viruses that has undergone a radiative evolution circa 7000 years ago, contemporaneously with agriculture intensification in mid Holocene. Maximum likelihood inference based on a set of 59 potyviruses and 38 plant species showed frequent host range changes during potyvirus evolution, with 4.6 changes per plant species on average, including 3.1 host gains and 1.5 host loss. These changes were quite recent, 74% of them being inferred on the terminal branches of the potyvirus tree. The most striking result was the high frequency of correlated host gains occurring repeatedly in different branches of the potyvirus tree, which raises the question of the dependence of the molecular and/or ecological mechanisms involved in adaptation to different plant species. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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26 pages, 3227 KiB

Open AccessArticle

The Expression of Potato Expansin A3 (StEXPA3) and Extensin4 (StEXT4) Genes with Distribution of StEXPAs and HRGPs-Extensin Changes as an Effect of Cell Wall Rebuilding in Two Types of PVY^NTN–Solanum tuberosum Interactions

by Katarzyna Otulak-Kozieł, Edmund Kozieł, Benham E. L. Lockhart and Józef J. Bujarski

Viruses 2020, 12(1), 66; https://0-doi-org.brum.beds.ac.uk/10.3390/v12010066 - 05 Jan 2020

Cited by 22 | Viewed by 2937

Abstract

The plant cell wall acts not only as a physical barrier, but also as a complex and dynamic structure that actively changes under different biotic and abiotic stress conditions. The question is, how are the different cell wall compounds modified during different interactions with exogenous stimuli such as pathogens? Plants exposed to viral pathogens respond to unfavorable conditions on multiple levels. One challenge that plants face under viral stress is the number of processes required for differential cell wall remodeling. The key players in these conditions are the cell wall genes and proteins, which can be regulated in specific ways during the interactions and have direct influences on the rebuilding of the cell wall structure. The cell wall modifications occurring in plants during viral infection remain poorly described. Therefore, this study focuses on cell wall dynamics as an effect of incompatible interactions between the potato virus Y (PVY^NTN) and resistant potatoes (hypersensitive plant), as well as compatible (susceptible plant) interactions. Our analysis describes, for the first time, the expression of the potato expansin A3 (StEXPA3) and potato extensin 4 (StEXT4) genes in PVY^NTN-susceptible and -resistant potato plant interactions. The results indicated a statistically significant induction of the StEXPA3 gene during a susceptible response. By contrast, we demonstrated the predominantly gradual activation of the StEXT4 gene during the hypersensitive response to PVY^NTN inoculation. Moreover, the in situ distributions of expansins (StEXPAs), which are essential cell wall-associated proteins, and the hydroxyproline-rich glycoprotein (HRGP) extensin were investigated in two types of interactions. Furthermore, cell wall loosening was accompanied by an increase in StEXPA deposition in a PVY^NTN-susceptible potato, whereas the HRGP content dynamically increased during the hypersensitive response, when the cell wall was reinforced. Ultrastructural localization and quantification revealed that the HRGP extensin was preferably located in the apoplast, but deposition in the symplast was also observed in resistant plants. Interestingly, during the hypersensitive response, StEXPA proteins were mainly located in the symplast area, in contrast to the susceptible potato where StEXPA proteins were mainly observed in the cell wall. These findings revealed that changes in the intracellular distribution and abundance of StEXPAs and HRGPs can be differentially regulated, depending on different types of PVY^NTN–potato plant interactions, and confirmed the involvement of apoplast and symplast activation as a defense response mechanism. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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20 pages, 4342 KiB

Open AccessArticle

Identifying Early Warning Signals for the Sudden Transition from Mild to Severe Tobacco Etch Disease by Dynamical Network Biomarkers

by Adrián Tarazona, Javier Forment and Santiago F. Elena

Viruses 2020, 12(1), 16; https://0-doi-org.brum.beds.ac.uk/10.3390/v12010016 - 20 Dec 2019

Cited by 8 | Viewed by 3028

Abstract

Complex systems exhibit critical thresholds at which they transition among alternative phases. Complex systems theory has been applied to analyze disease progression, distinguishing three stages along progression: (i) a normal noninfected state; (ii) a predisease state, in which the host is infected and responds and therapeutic interventions could still be effective; and (iii) an irreversible state, where the system is seriously threatened. The dynamical network biomarker (DNB) theory sought for early warnings of the transition from health to disease. Such DNBs might range from individual genes to complex structures in transcriptional regulatory or protein–protein interaction networks. Here, we revisit transcriptomic data obtained during infection of tobacco plants with tobacco etch potyvirus to identify DNBs signaling the transition from mild/reversible to severe/irreversible disease. We identified genes showing a sudden transition in expression along disease categories. Some of these genes cluster in modules that show the properties of DNBs. These modules contain both genes known to be involved in response to pathogens (e.g., ADH2, CYP19, ERF1, KAB1, LAP1, MBF1C, MYB58, PR1, or TPS5) and other genes not previously related to biotic stress responses (e.g., ABCI6, BBX21, NAP1, OSM34, or ZPN1). Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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24 pages, 20656 KiB

Open AccessArticle

A Novel Interaction Network Used by Potyviruses in Virus–Host Interactions at the Protein Level

by Marjo Ala-Poikela, Minna-Liisa Rajamäki and Jari P.T. Valkonen

Viruses 2019, 11(12), 1158; https://0-doi-org.brum.beds.ac.uk/10.3390/v11121158 - 14 Dec 2019

Cited by 18 | Viewed by 5071

Abstract

Host proteins that are central to infection of potyviruses (genus Potyvirus; family Potyviridae) include the eukaryotic translation initiation factors eIF4E and eIF(iso)4E. The potyviral genome-linked protein (VPg) and the helper component proteinase (HCpro) interact with each other and with eIF4E and eIF(iso)4E and proteins are involved in the same functions during viral infection. VPg interacts with eIF4E/eIF(iso)4E via the 7-methylguanosine cap-binding region, whereas HCpro interacts with eIF4E/eIF(iso)4E via the 4E-binding motif YXXXXLΦ, similar to the motif in eIF4G. In this study, HCpro and VPg were found to interact in the nucleus, nucleolus, and cytoplasm in cells infected with the potyvirus potato virus A (PVA). In the cytoplasm, interactions between HCpro and VPg occurred in punctate bodies not associated with viral replication vesicles. In addition to HCpro, the 4E-binding motif was recognized in VPg of PVA. Mutations in the 4E-binding motif of VPg from PVA weakened interactions with eIF4E and heavily reduced PVA virulence. Furthermore, mutations in the 4G-binding domain of eIF4E reduced interactions with VPg and abolished interactions with HCpro. Thus, HCpro and VPg can both interact with eIF4E using the 4E-binding motif. Our results suggest a novel interaction network used by potyviruses to interact with host plants via translation initiation factors. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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27 pages, 3925 KiB

Open AccessArticle

Potato Virus Y Infection Alters Small RNA Metabolism and Immune Response in Tomato

by Maria I. Prigigallo, Maja Križnik, Domenico De Paola, Domenico Catalano, Kristina Gruden, Mariella M. Finetti-Sialer and Fabrizio Cillo

Viruses 2019, 11(12), 1100; https://0-doi-org.brum.beds.ac.uk/10.3390/v11121100 - 27 Nov 2019

Cited by 23 | Viewed by 4662

Abstract

Potato virus Y (PVY) isolate PVY^C-to induces growth reduction and foliar symptoms in tomato, but new vegetation displays symptom recovery at a later stage. In order to investigate the role of micro(mi)RNA and secondary small(s)RNA-regulated mechanisms in tomato defenses against PVY, we performed sRNA sequencing from healthy and PVY^C-to infected tomato plants at 21 and 30 days post-inoculation (dpi). A total of 792 miRNA sequences were obtained, among which were 123 canonical miRNA sequences, many isomiR variants, and 30 novel miRNAs. MiRNAs were mostly overexpressed in infected vs. healthy plants, whereas only a few miRNAs were underexpressed. Increased accumulation of isomiRs was correlated with viral infection. Among miRNA targets, enriched functional categories included resistance (R) gene families, transcription and hormone factors, and RNA silencing genes. Several 22-nt miRNAs were shown to target R genes and trigger the production of 21-nt phased sRNAs (phasiRNAs). Next, 500 phasiRNA-generating loci were identified, and were shown to be mostly active in PVY-infected tissues and at 21 dpi. These data demonstrate that sRNA-regulated host responses, encompassing miRNA alteration, diversification within miRNA families, and phasiRNA accumulation, regulate R and disease-responsive genes. The dynamic regulation of miRNAs and secondary sRNAs over time suggests a functional role of sRNA-mediated defenses in the recovery phenotype. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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15 pages, 6765 KiB

Open AccessArticle

Comparison of Transcriptome Differences in Soybean Response to Soybean Mosaic Virus under Normal Light and in the Shade

by Lei Zhang, Jing Shang, Wenming Wang, Junbo Du, Kai Li, Xiaoling Wu, Liang Yu, Chunyan Liu, Muhammad Ibrahim Khaskheli and Wenyu Yang

Viruses 2019, 11(9), 793; https://0-doi-org.brum.beds.ac.uk/10.3390/v11090793 - 29 Aug 2019

Cited by 20 | Viewed by 3662

Abstract

Shading in the intercropping system is a major abiotic factor which influences soybean growth and development, while soybean mosaic virus (SMV) is a biotic factor that limits the yield and quality of soybean. However, little is known about the defense response of soybean to SMV in the shade. Thus, in the current study, both intensity and quality (red:far-red, R:FR) of the light were changed to simulate the shaded environment and comparative transcriptome analysis was performed. Morphologically, plant growth was inhibited by SMV, which decreased 35.93% of plant height and 8.97% of stem diameter in the shade. A total of 3548 and 4319 differentially expressed genes (DEGs) were identified in soybean plants infected with SMV under normal light and in the shade. Enrichment analysis showed that the plant defense-related genes were upregulated under normal light but downregulated in the shade. Pathways that were repressed include plant-pathogen interaction, secondary metabolism, sugar metabolism, and vitamin metabolism. In addition, genes associated with signaling pathways such as salicylic acid (SA), jasmonic acid (JA), and ethylene (ETH) were also downregulated in the shade. A qRT-PCR assay of 15 DEGs was performed to confirm transcriptome results. According to our knowledge, this is the first report on soybean response to dual stress factors. These results provide insights into the molecular mechanisms in which soybean plants were infected with SMV in the shade. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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Review

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15 pages, 1266 KiB

Open AccessReview

Functional Characterization of Pepper Vein Banding Virus-Encoded Proteins and Their Interactions: Implications in Potyvirus Infection

by Pallavi Sabharwal and Handanahal S. Savithri

Viruses 2020, 12(9), 1037; https://0-doi-org.brum.beds.ac.uk/10.3390/v12091037 - 17 Sep 2020

Cited by 3 | Viewed by 3142

Abstract

Pepper vein banding virus (PVBV) is a distinct species in the Potyvirus genus which infects economically important plants in several parts of India. Like other potyviruses, PVBV encodes multifunctional proteins, with several interaction partners, having implications at different stages of the potyviral infection. In this review, we summarize the functional characterization of different PVBV-encoded proteins with an emphasis on their interaction partners governing the multifunctionality of potyviral proteins. Intrinsically disordered domains/regions of these proteins play an important role in their interactions with other proteins. Deciphering the function of PVBV-encoded proteins and their interactions with cognitive partners will help in understanding the putative mechanisms by which the potyviral proteins are regulated at different stages of the viral life-cycle. This review also discusses PVBV virus-like particles (VLPs) and their potential applications in nanotechnology. Further, virus-like nanoparticle-cell interactions and intracellular fate of PVBV VLPs are also discussed. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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17 pages, 982 KiB

Open AccessReview

Plant Molecular Responses to Potato Virus Y: A Continuum of Outcomes from Sensitivity and Tolerance to Resistance

by Špela Baebler, Anna Coll and Kristina Gruden

Viruses 2020, 12(2), 217; https://0-doi-org.brum.beds.ac.uk/10.3390/v12020217 - 15 Feb 2020

Cited by 34 | Viewed by 6602

Abstract

Potato virus Y (PVY) is the most economically important virus affecting potato production. PVY manipulates the plant cell machinery in order to successfully complete the infecting cycle. On the other side, the plant activates a sophisticated multilayer immune defense response to combat viral infection. The balance between these mechanisms, depending on the plant genotype and environment, results in a specific outcome that can be resistance, sensitivity, or tolerance. In this review, we summarize and compare the current knowledge on molecular events, leading to different phenotypic outcomes in response to PVY and try to link them with the known molecular mechanisms. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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30 pages, 7780 KiB

Open AccessReview

The Potyviruses: An Evolutionary Synthesis Is Emerging

by Adrian J. Gibbs, Mohammad Hajizadeh, Kazusato Ohshima and Roger A.C. Jones

Viruses 2020, 12(2), 132; https://0-doi-org.brum.beds.ac.uk/10.3390/v12020132 - 22 Jan 2020

Cited by 72 | Viewed by 6578

Abstract

In this review, encouraged by the dictum of Theodosius Dobzhansky that “Nothing in biology makes sense except in the light of evolution”, we outline the likely evolutionary pathways that have resulted in the observed similarities and differences of the extant molecules, biology, distribution, etc. of the potyvirids and, especially, its largest genus, the potyviruses. The potyvirids are a family of plant-infecting RNA-genome viruses. They had a single polyphyletic origin, and all share at least three of their genes (i.e., the helicase region of their CI protein, the RdRp region of their NIb protein and their coat protein) with other viruses which are otherwise unrelated. Potyvirids fall into 11 genera of which the potyviruses, the largest, include more than 150 distinct viruses found worldwide. The first potyvirus probably originated 15,000–30,000 years ago, in a Eurasian grass host, by acquiring crucial changes to its coat protein and HC-Pro protein, which enabled it to be transmitted by migrating host-seeking aphids. All potyviruses are aphid-borne and, in nature, infect discreet sets of monocotyledonous or eudicotyledonous angiosperms. All potyvirus genomes are under negative selection; the HC-Pro, CP, Nia, and NIb genes are most strongly selected, and the PIPO gene least, but there are overriding virus specific differences; for example, all turnip mosaic virus genes are more strongly conserved than those of potato virus Y. Estimates of dN/dS (ω) indicate whether potyvirus populations have been evolving as one or more subpopulations and could be used to help define species boundaries. Recombinants are common in many potyvirus populations (20%–64% in five examined), but recombination seems to be an uncommon speciation mechanism as, of 149 distinct potyviruses, only two were clear recombinants. Human activities, especially trade and farming, have fostered and spread both potyviruses and their aphid vectors throughout the world, especially over the past five centuries. The world distribution of potyviruses, especially those found on islands, indicates that potyviruses may be more frequently or effectively transmitted by seed than experimental tests suggest. Only two meta-genomic potyviruses have been recorded from animal samples, and both are probably contaminants. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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14 pages, 974 KiB

Open AccessReview

The RNA-Dependent RNA Polymerase NIb of Potyviruses Plays Multifunctional, Contrasting Roles during Viral Infection

by Wentao Shen, Yan Shi, Zhaoji Dai and Aiming Wang

Viruses 2020, 12(1), 77; https://0-doi-org.brum.beds.ac.uk/10.3390/v12010077 - 08 Jan 2020

Cited by 43 | Viewed by 5396

Abstract

Potyviruses represent the largest group of known plant RNA viruses and include many agriculturally important viruses, such as Plum pox virus, Soybean mosaic virus, Turnip mosaic virus, and Potato virus Y. Potyviruses adopt polyprotein processing as their genome expression strategy. Among the 11 known viral proteins, the nuclear inclusion protein b (NIb) is the RNA-dependent RNA polymerase responsible for viral genome replication. Beyond its principal role as an RNA replicase, NIb has been shown to play key roles in diverse virus–host interactions. NIb recruits several host proteins into the viral replication complexes (VRCs), which are essential for the formation of functional VRCs for virus multiplication, and interacts with the sumoylation pathway proteins to suppress NPR1-mediated immunity response. On the other hand, NIb serves as a target of selective autophagy as well as an elicitor of effector-triggered immunity, resulting in attenuated virus infection. These contrasting roles of NIb provide an excellent example of the complex co-evolutionary arms race between plant hosts and potyviruses. This review highlights the current knowledge about the multifunctional roles of NIb in potyvirus infection, and discusses future research directions. Full article

(This article belongs to the Special Issue The Complexity of the Potyviral Interaction Network)

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