Expression, localization and effects on virulence of the cysteine-rich 8 kDa protein of Potato mop-top virus

Abstract

Potato mop-top virus (PMTV) RNA3 contains a triple gene block (TGB) encoding viral movement proteins and an open reading frame for a putative 8 kDa cysteine-rich protein (CRP). In this study, PMTV CRP was shown to be expressed in the course of virus infection, and a PMTV CRP-specific subgenomic RNA was mapped. CRP has previously been shown to be dispensable for infection of PMTV in Nicotiana benthamiana. In this study, PMTV CRP was found to increase the severity of disease symptoms when expressed from Potato virus X or Tobacco mosaic virus in N. benthamiana and Nicotiana tabacum, suggesting that the protein affects virulence of the virus or might suppress a host defence mechanism. However, PMTV CRP did not show RNA silencing suppression activity in three assays. Host responses to the PMTV CRP expression from different viral genomes ranged from an absence of response to extreme resistance at a single cell level and were dependent on the viral genome. These findings emphasized involvement of viral proteins and/or virus-induced cell components in the plant reaction to CRP. PMTV CRP was predicted to possess a transmembrane segment. CRP fused to the green fluorescent protein was associated with endoplasmic reticulum-derived membranes and induced dramatic rearrangements of the endoplasmic reticulum structure, which might account for protein functions as a virulence factor of the virus.

Role of the zinc-finger and basic motifs of chrysanthemum virus B p12 protein in nucleic acid binding, protein localization and induction of a hypersensitive response upon expression from a viral vector

“…These data demonstrated that the expressed protein (p12BM) rather than the p12BM gene sequence itself suppressed PVX infection. A similar effect was observed when the CRP of potato mop-top virus was expressed from barley stripe mosaic virus (Lukhovitskaya et al, 2005a). Additionally, the inability of PVX-p12BM-stop to induce an HR implied that the p12 protein, but not the sequence encoding it, is involved in HR induction in PVX-p12-infected plants.…”

Diversity and evolution of potato mop-top virus

“…This has also been observed for other proteins with silencing suppressor activities, such as 16K of tobacco rattle virus and p14 of beet necrotic yellow vein virus [4,18]. Because the 8K protein acts as a virulence factor [13], the differences …”

“…The fourth ORF of RNA-TGB encodes a putative cysteine-rich protein (8K protein), which appears to enhance the virulence of the virus and to act as a weak RNA silencing suppressor [13,14].…”

“…The aa sequences within the groups 8K-A and 8K-B were very similar (98.1-100 % and 98.6-100 % identity, respectively) whereas the two groups differed at eight positions. Most differences were located in the central highly hydrophobic region of the protein [13]. The translation start codon AUG (group 8K-A) for the 8K protein was, in most sequences (8K-B), replaced by the putatively less efficient GUG [11,13].…”

Tyrosine Phosphorylation of the Triple Gene Block Protein 3 Regulates Cell-to-Cell Movement and Protein Interactions of Potato Mop-Top Virus

“…RNA3 contains four open reading frames (ORFs) predicted to encode the TGB proteins TGBp1 (51K), TGBp2 (13K), and TGBp3 (21K) and an 8K cysteine-rich protein (19)(20)(21) (Fig. 1A).…”