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A novel sweet potato potyvirus open reading frame (ORF) is expressed via polymerase slippage and suppresses RNA silencing

View Article: PubMed Central - PubMed

ABSTRACT

The single‐stranded, positive‐sense RNA genome of viruses in the genus Potyvirus encodes a large polyprotein that is cleaved to yield 10 mature proteins. The first three cleavage products are P1, HCpro and P3. An additional short open reading frame (ORF), called pipo, overlaps the P3 region of the polyprotein ORF. Four related potyviruses infecting sweet potato (Ipomoea batatas) are predicted to contain a third ORF, called pispo, which overlaps the 3′ third of the P1 region. Recently, pipo has been shown to be expressed via polymerase slippage at a conserved GA6 sequence. Here, we show that pispo is also expressed via polymerase slippage at a GA6 sequence, with higher slippage efficiency (∼5%) than at the pipo site (∼1%). Transient expression of recombinant P1 or the ‘transframe’ product, P1N‐PISPO, in Nicotiana benthamiana suppressed local RNA silencing (RNAi), but only P1N‐PISPO inhibited short‐distance movement of the silencing signal. These results reveal that polymerase slippage in potyviruses is not limited to pipo expression, but can be co‐opted for the evolution and expression of further novel gene products.

No MeSH data available.


Related in: MedlinePlus

Locations of GW/WG sequences in P1 and P1N‐PISPO proteins of Sweet potato feathery mottle virus (SPFMV)‐group viruses. Schematic diagram of the P1 protein of Sweet potato mild mottle virus (SPMMV) and the P1 and P1N‐PISPO proteins of SPFMV‐group viruses, showing the positions of GW/WG sequences. The P1 sequence is indicated in light blue; the PISPO sequence is indicated in pink. GW/WG sequences are indicated by vertical coloured lines, with homologous instances (by blastp alignment) indicated with the same colour. SPV2, Sweet potato virus 2; SPVC, Sweet potato virus C; SPVG, Sweet potato virus G.
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mpp12366-fig-0005: Locations of GW/WG sequences in P1 and P1N‐PISPO proteins of Sweet potato feathery mottle virus (SPFMV)‐group viruses. Schematic diagram of the P1 protein of Sweet potato mild mottle virus (SPMMV) and the P1 and P1N‐PISPO proteins of SPFMV‐group viruses, showing the positions of GW/WG sequences. The P1 sequence is indicated in light blue; the PISPO sequence is indicated in pink. GW/WG sequences are indicated by vertical coloured lines, with homologous instances (by blastp alignment) indicated with the same colour. SPV2, Sweet potato virus 2; SPVC, Sweet potato virus C; SPVG, Sweet potato virus G.

Mentions: Further inspection of the amino acid sequence revealed WG/GW (‘AGO‐hook’) motifs. Such motifs play a key role within the P1‐N domain of SPMMV P1 (Giner et al., 2010) and some other plant viral silencing suppressors (Azevedo et al., 2010; de Ronde et al., 2014). Among 31 sequenced isolates, the PISPO sequences contain between one and three GW/WG motifs, whereas full‐length P1 and full‐length P1N‐PISPO contain between two and four GW/WG motifs (Fig. 5). It should be noted, however, that WG/GW di‐amino acids are not particularly uncommon in generic protein sequences.


A novel sweet potato potyvirus open reading frame (ORF) is expressed via polymerase slippage and suppresses RNA silencing
Locations of GW/WG sequences in P1 and P1N‐PISPO proteins of Sweet potato feathery mottle virus (SPFMV)‐group viruses. Schematic diagram of the P1 protein of Sweet potato mild mottle virus (SPMMV) and the P1 and P1N‐PISPO proteins of SPFMV‐group viruses, showing the positions of GW/WG sequences. The P1 sequence is indicated in light blue; the PISPO sequence is indicated in pink. GW/WG sequences are indicated by vertical coloured lines, with homologous instances (by blastp alignment) indicated with the same colour. SPV2, Sweet potato virus 2; SPVC, Sweet potato virus C; SPVG, Sweet potato virus G.
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mpp12366-fig-0005: Locations of GW/WG sequences in P1 and P1N‐PISPO proteins of Sweet potato feathery mottle virus (SPFMV)‐group viruses. Schematic diagram of the P1 protein of Sweet potato mild mottle virus (SPMMV) and the P1 and P1N‐PISPO proteins of SPFMV‐group viruses, showing the positions of GW/WG sequences. The P1 sequence is indicated in light blue; the PISPO sequence is indicated in pink. GW/WG sequences are indicated by vertical coloured lines, with homologous instances (by blastp alignment) indicated with the same colour. SPV2, Sweet potato virus 2; SPVC, Sweet potato virus C; SPVG, Sweet potato virus G.
Mentions: Further inspection of the amino acid sequence revealed WG/GW (‘AGO‐hook’) motifs. Such motifs play a key role within the P1‐N domain of SPMMV P1 (Giner et al., 2010) and some other plant viral silencing suppressors (Azevedo et al., 2010; de Ronde et al., 2014). Among 31 sequenced isolates, the PISPO sequences contain between one and three GW/WG motifs, whereas full‐length P1 and full‐length P1N‐PISPO contain between two and four GW/WG motifs (Fig. 5). It should be noted, however, that WG/GW di‐amino acids are not particularly uncommon in generic protein sequences.

View Article: PubMed Central - PubMed

ABSTRACT

The single‐stranded, positive‐sense RNA genome of viruses in the genus Potyvirus encodes a large polyprotein that is cleaved to yield 10 mature proteins. The first three cleavage products are P1, HCpro and P3. An additional short open reading frame (ORF), called pipo, overlaps the P3 region of the polyprotein ORF. Four related potyviruses infecting sweet potato (Ipomoea batatas) are predicted to contain a third ORF, called pispo, which overlaps the 3′ third of the P1 region. Recently, pipo has been shown to be expressed via polymerase slippage at a conserved GA6 sequence. Here, we show that pispo is also expressed via polymerase slippage at a GA6 sequence, with higher slippage efficiency (∼5%) than at the pipo site (∼1%). Transient expression of recombinant P1 or the ‘transframe’ product, P1N‐PISPO, in Nicotiana benthamiana suppressed local RNA silencing (RNAi), but only P1N‐PISPO inhibited short‐distance movement of the silencing signal. These results reveal that polymerase slippage in potyviruses is not limited to pipo expression, but can be co‐opted for the evolution and expression of further novel gene products.

No MeSH data available.


Related in: MedlinePlus