Key Amino Acids for Pepper Vein Yellows Virus P0 Protein Pathogenicity, Gene Silencing, and Subcellular Localization

Pepper vein yellows virus (PeVYV) is a newly recognized Polerovirus extracted from Chinese pepper. The symptoms of PeVYV-infested pepper plants comprise intervein yellow staining, leaf curl formation and other malformations, and leaf internodal shrinkage, but the roles of the viral proteins remain undetermined. The P0 protein of the genus Polerovirus has established post-transcriptional gene silencing (PTGS) activity. This investigation focused on the PeVYV-encoded P0 protein and assessed its potential virulence capacity, PTGS activity, and tendencies to localize in the nucleus. This study revealed that P0 influenced the pathogenic properties of a specific heterologous potato virus X. In addition, P0 proteins impaired local gene silencing, although they did not regulate generalized gene silencing within Nicotiana benthamiana 16c plants. Furthermore, P0 proteins localized mainly in the nucleus, particularly in the nucleolus. P0 deletion mutagenesis demonstrated that the F-box motif (56–72 amino acids, AAs) of P0 was essential for symptom determination, inhibition of PTGS, and subcellular localization. Mutation analysis of the F-box motif of P0 protein indicated that AA 57 of the P0 protein was a pivotal site in symptom development and that AA 56 of the P0 protein was indispensable for inhibiting PTGS and subcellular localization. The outcomes obtained here suggest that further studies should be conducted on the molecular mechanisms of amino acids of the F-box domain of P0 protein in the interaction of PeVYV with plants.

Distribution and identification of luteovirids affecting chickpea in Sudan

In Sudan yellowing viruses are key production constraints in pulse crops. Field surveys were carried out to identify luteovirids affecting chickpea crops in the major production regions (Gezira Scheme and River Nile State). A total of 415 chickpea plant samples with yellowing and stunting symptoms were collected during the 2013, 2015 and 2018 growing seasons. Serological results (Tissue-blot immunoassays) showed that Luteoviridae and Chickpea chlorotic dwarf virus (CpCDV, genus Mastrevirus, family Geminiviridae) were the most common viruses, with rare infections with Faba bean necrotic yellows virus (FBNYV, genus Nanovirus, family Nanoviridae). Some samples reacted only with a broad-spectrum luteovirid monoclonal antibody (5G4-MAb), and others showed cross reactions between the specific monoclonal antibodies, suggesting the occurrence of new luteovirid variants. Serological results were confirmed by amplification with reverse transcription-polymerase chain reaction (RT-PCR) and sequencing of the partial coat protein gene. Molecular analyses provided a basic, sufficient and reliable characterization for four viruses affecting chickpea that belong to Polerovirus (family Luteoviridae). These were Cucurbit aphid-borne yellows virus (CABYV), Pepper vein yellows virus (PeVYV), Pepo aphid-borne yellows virus (PABYV) and Cotton leafroll dwarf virus (CLRDV), that shared high similarity with the type sequences. Phylogenetic analyses also revealed high similarity to luteovirid species. This study has established reliable, rapid and sensitive molecular tools for the detection of luteovirid species.

Biological and Genetic Characterization of Pod Pepper Vein Yellows Virus-Associated RNA From Capsicum frutescens in Wenshan, China

Tombusvirus-like associated RNAs (tlaRNAs) are positive-sense single-stranded RNAs found in plants co-infected with some viruses of the genus Polerovirus. Pod pepper vein yellows virus (PoPeVYV) was recently reported as a new recombinant polerovirus causing interveinal yellowing, stunting, and leaf rolling in Capsicum frutescens plants at Wenshan city, Yunnan province, China. The complete genome sequence of its associated RNA has now been determined by next-generation sequencing and reverse transcription (RT) polymerase chain reaction (PCR). PoPeVYV-associated RNA (PoPeVYVaRNA) (GenBank Accession No. MW323470) has 2970 nucleotides and is closely related to other group II tlaRNAs, particularly tobacco bushy top disease-associated RNA (TBTDaRNA, GenBank Accession No. EF529625). In infection experiments on Nicotiana benthamiana and C. frutescens plants, synergism between PoPeVYVaRNA and PoPeVYV was demonstrated, leading to severe interveinal yellowing of leaves and stunting of plants. The results provide further information on the genetic and biological properties of the various agents associated with pepper vein yellows disease (PeVYD).

Pod pepper vein yellows virus, a new recombinant polerovirus infecting Capsicum frutescens in Yunnan province, China

Pepper vein yellows viruses (PeVYV) are phloem-restricted viruses in the genus Polerovirus, family Luteoviridae. Typical viral symptoms of PeVYV including interveinal yellowing of leaves and upward leaf curling were observed in pod pepper plants (Capsicum frutescens) growing in Wenshan city, Yunnan province, China. The complete genome sequence of a virus from a sample of these plants was determined by next-generation sequencing and RT-PCR. Pod pepper vein yellows virus (PoPeVYV) (MT188667) has a genome of 6015 nucleotides, and the characteristic genome organization of a member of the genus Polerovirus. In the 5′ half of its genome (encoding P0 to P4), PoPeVYV is most similar (93.1% nt identity) to PeVYV-3 (Pepper vein yellows virus 3) (KP326573) but diverges greatly in the 3′-part encoding P5, where it is most similar (91.7% nt identity) to tobacco vein distorting virus (TVDV, EF529624) suggesting a recombinant origin. Recombination analysis predicted a single recombination event affecting nucleotide positions 4126 to 5192 nt, with PeVYV-3 as the major parent but with the region 4126–5192 nt derived from TVDV as the minor parent. A full-length clone of PoPeVYV was constructed and shown to be infectious in C. frutescens by RT-PCR and the presence of icosahedral viral particles.

Pod pepper vein yellows virus, a new recombinant polerovirus infecting Capsicum frutescens in Yunnan province, China

Pepper vein yellows viruses (PeVYV) are phloem-restricted viruses in the genus Polerovirus, family Luteoviridae. Typical viral symptoms of PeVYV including interveinal yellowing of leaves and upward leaf curling were observed in pod pepper plants (Capsicum frutescens) growing in Wenshan city, Yunnan province, China. The complete genome sequence of a virus from a sample of these plants was determined by next-generation sequencing and RT-PCR. Pod pepper vein yellows virus (PoPeVYV) (MT188667) has a genome of 6015 nucleotides, and the characteristic genome organization of a member of the genus Polerovirus. In the 5’ half of its genome (encoding P0 to P4), PoPeVYV is most similar (93.1% nt identity) to PeVYV-3 (Pepper vein yellows virus 3) (KP326573) but diverges greatly in the 3’-part encoding P5, where it is most similar (91.7% nt identity) to tobacco vein distorting virus (TVDV, EF529624) suggesting a recombinant origin. Recombination analysis predicted a single recombination event affecting nucleotide positions 4126 to 5192 nt, with PeVYV-3 as the major parent but with the region 4126-5192 nt derived from TVDV as the minor parent. A full-length clone of PoPeVYV was constructed and shown to be infectious in C. frutescens by RT-PCR and the presence of icosahedral viral particles.

Complete Genome Sequence of Novel Polerovirus-Associated RNA Infecting Pepper (Capsicum spp.) in South Africa

ABSTRACT The complete genome sequence of a novel polerovirus-associated RNA infecting pepper in South Africa was determined. The nucleotide sequence identity of 78.3% with closely related species suggested that this associated RNA was novel, and the name pepper vein yellows virus-associated RNA is proposed for this RNA fragment.

Non-transmissibility of Pepper whitefly borne vein yellows virus (PeWBVYV) by the Mediterranean species of Bemisia tabaci and identification of a candidate insect receptor protein for poleroviruses

Recent reports of transmission of poleroviruses by whiteflies is indicative of evolution of new virus-vector relationships. Pepper whitefly-borne vein yellows virus (PeWBVYV), was the first report of a polerovirus infecting pepper in Israel which was transmitted by whiteflies (MEAM1) and not aphids. This study reports the inability of the Mediterranean species (MED, Q biotype) of B. tabaci to transmit PeWBVYV. However we show that non-transmission of PeWBVYV by MED is not due to the lack of interaction with the GroEL protein of the Hamiltonella symbiont. Although not transmitted by MED, PeWBVYV was detected in its hemolymph, indicating its translocation across the MED midgut barrier. The aphid transmitted Pepper vein yellows virus 2 (PeVYV-2) was also detected in the hemolymph of MEAM1 whiteflies but PeWBVYV could not be detected in the aphid hemolymph. Interestingly, relative amounts of PeWBVYV in the hemolymph of the, MED was much lower than in hemolymph of MEAM1 whiteflies. We also identified a candidate receptor protein, complement component 1Q sub-complement binding protein (C1QBP) which interacts with the capsid proteins of PeWBVYV and PeVYV-2 but not with the whitefly transmitted Tomato yellow leaf curl virus by a yeast two-hybrid approach using the minor capsid protein (RTD) as bait to screen for interacting proteins against the whitefly cDNA library. C1QBP, is a known receptor of bacterial and viral pathogens but this is the first report of its interaction with a plant virus.

Pod Pepper Vein Yellows Virus, a New Recombinant Polerovirus Infecting Pod Pepper in Yunnan Province, China

Pepper vein yellows viruses (PeVYV) are phloem-restricted viruses in the genus Polerovirus, family Luteoviridae. Typical viral symptoms of PeVYV including interveinal yellowing of leaves and upward leaf curling were observed in pod pepper plants (Capsicum frutescens) growing in Wenshan city, Yunnan province, China. The complete genome sequence of a virus from a sample of these plants was determined by next-generation sequencing and RT-PCR. Pod pepper vein yellows virus (PoPeVYV) (MT188667) has a genome of 6015 nucleotides, and the characteristic genome organization of a member of the genus Polerovirus. In the 5’ half of its genome (encoding P0 to P4), PoPeVYV is most similar (94% nt identity) to PeVYV-3 (Pepper vein yellows virus 3) (KP326573) but diverges greatly in the 3’-part encoding P5, where it is most similar (88.8% nt identity) to tobacco vein distorting virus (TVDV, EF529624) suggesting a recombinant origin. Recombination analysis predicted a single recombination event at nucleotide positions 4126 to 5192 nt, with TVDV and PeVYV-3 as the minor and major parents, respectively. A full-length clone of PoPeVYV was constructed and shown to be infectious in C. frutescens by RT-PCR and the presence of icosahedral viral particles.

Competitive Interactions Between Whitefly and Aphid Transmitted Poleroviruses within the Plant Host and the Insect Vectors

Pepper cultivation in Israel has recently been constrained by two sympatric poleroviruses, Pepper vein yellows virus-2 (PeVYV-2) and Pepper whitefly-borne vein yellows virus (PeWBVYV) which are transmitted specifically by aphids and whiteflies, respectively. The interaction between PeVYV-2 and PeWBVYV inside the host plant and the insect vectors were investigated in this study. Our results show that PeVYV-2 and PeWBVYV compete against each other inside the host plant and also inside aphids. PeWBVYV was the weaker competitor inside the host plant with diminished transmission rates when inoculated simultaneously or successively after PeVYV-2 and could only be transmitted efficiently when inoculated first and then challenged by PeVYV-2. Successive inoculations of plants with viruliferous whiteflies with PeWBVYV, followed by viruliferous aphids with PeVYV-2 led to co-infection rate of 60%, however with severely reduced titers of PeWBVYV in the co-infected plants compared to singly infected ones. In contrast, PeVYV-2 was the weaker competitor inside the insect vector with reduced quantities of the acquired virus and reduced transmission rate by aphids when given prior acquisition on PeWBVYV. However, we also show that transmission efficiency of PeVYV-2 and PeWBVYV from co-infected plants by whiteflies and aphids remain comparable to that from singly-infected plants. This is probably due to the reduced titers of PeWBVYV inside co-infected plants causing lesser impact on transmission of PeVYV-2 by aphids and the stronger competitiveness of PeWBVYV inside whitefly. Competitive interactions between PeVYV-2 and PeWBVYV inside the host plant and insect vector can thus be beneficial for their co-existence.