2b ORFs encoded by subgroup IB strains of cucumber mosaic virus induce differential virulence on Nicotiana species

Abstract

Cucumber mosaic virus (CMV)-encoded 2b protein from subgroup IA or subgroup II was shown to be a determinant of virulence in many solanaceous hosts. In this study, the virulence of 2b proteins from subgroup IB strains was analysed using four intraspecies hybrid viruses, which were generated by precise replacement of the 2b open reading frame (ORF) in subgroup IA strain Fny-CMV with the 2b ORFs of four subgroup IB strains, Cb7-CMV, PGs-CMV, Rad35-CMV and Na-CMV, generating FCb7 2b -CMV, FPGs 2b -CMV, FRad35 2b -CMV and FNa 2b -CMV, respectively. FCb7 2b -CMV was more virulent than Fny-CMV, and was similar in phenotype to its parental virus Cb7-CMV on the three Nicotiana species tested. FNa 2b -CMV also was virulent on these host species, equivalent to Fny-CMV or Na-CMV. However, FRad35 2b -CMV only caused mild mosaic or undetectable symptoms on all the host species tested, and was less virulent than Fny-CMV or Rad35-CMV. FPGs 2b -CMV infected all the host species systemically, and induced either mosaic or barely visible symptoms, demonstrating that the inability of PGs-CMV to infect these three Nicotiana species was not due to its 2b protein. The diverse virulence was shown to be mediated by the 2b proteins rather than the C-terminal overlapping parts of the 2a proteins, and was associated with the level of viral progeny RNA accumulation in systemically infected leaves, but not with the rate of long-distance viral movement in host plants. Through analysis of encapsidation of viral RNAs, there was an apparent correlation between the virulence and the high level of encapsidated RNA 2 in virions of Fny-CMV, FCb7 2b -CMV and FNa 2b -CMV.

Phylogenetic Analysis of New Isolates of Cucumber mosaic virus from Iran on the Basis of Different Genomic Regions

“…Isolates in S-IA clade induced mosaic on squash, mild shoestring on tomato and mild mosaic on tobacco cultivars and N. benthamiana. This is also in agreement with a previous report that S-IB isolates are more virulent than S-IA isolates (Du et al, 2007). The CP nucleotide and amino acid identities of isolates characterized in this study and that of other S-IB isolates were both 91−99%.…”

“…Protein 2b is expressed from RNA 4A, a subgenomic RNA derived from RNA2, is involved in the long-distance movement of CMV in the plant (Soards et al, 2002) and functions as a suppressor of RNA silencing (Ding et al, 1994;Li et al, 1999). Many strains and isolates of CMV have been characterized on the basis of symptoms and host range (Choi et al, 2005;Huppert et al, 2002;Palukaitis and Garcia-Arenal, 2003) and often, differences in such phenotypes were mapped to the genomic RNAs that code for the CP (Shintaku et al, 1992;Sugiyama et al, 2000;Suzuki et al, 1995), MP (Choi et al, 2005) or 2b protein (Du et al, 2007;Shi et al, 2002;Lewsey et al, 2009Lewsey et al, , 2010.…”

Accurate and Efficient Data Processing for Quantitative Real-Time PCR using a Tripartite Plant Virus as a Model

“…Our previous work showed that a change of CMV virulence resulted from different accumulation of viral RNAs, which is induced by either replacement of 2b ORFs or by addition of sat RNAs (10,11). In this study, we propose equations to quantify the accumulation ratios of CMV RNAs 1, 2, and 3 in the same sample or between different samples, by analyzing the results of real-time PCR using SCF, LinRegPCR, and DART methods.…”

“…Huangmiaoyu) were used as host plants and grown in a greenhouse between 21-26C. The wild-type Fny-CMV and four intraspecies hybrid viruses FCb7 2b -CMV, FRad35 2b -CMV, FBX 2b -CMV, and FNa 2b -CMV were generated as described (11). All viral strains were inoculated with the same concentrations on tobacco seedlings at the four- to sixleaf stage.…”

Behavior of RNAi suppressor protein 2b of Cucumber mosaic virus in planta in presence and absence of virus

“…The main difference in virulence was shown to be mediated by differences in the respective 2b proteins [24,25,30]. The CMV 2b protein localizes in the nucleus via an arginine-rich nuclear localization signal (NLS).…”