Disease relevance of CMVs2gp2

• Cucumber mosaic virus (CMV)-encoded 2b protein was among the first suppressors identified that could inhibit post-transcriptional gene silencing (PTGS), but with little or no effect on miRNA functions [1].
• Ilarviruses encode a Cucumovirus-like 2b gene that is absent in other genera within the Bromoviridae [2].
• The P1/HC-Pro sequence of plant potyviruses and the 2b gene of the cucumber mosaic virus have been shown to interfere with PTGS [3].
• Moreover, a protein species of the size expected for SpLV ORF 2b was translated in vitro from the RNA 4A-containing virion RNAs [2].
• Mutation of the 16K gene could be overcome by expression from RNA2 of the Cucumber mosaic virus 2b gene, the Soil-borne wheat mosaic virus 19K gene, or the Barley stripe mosaic virus gammab gene, indicating that the proteins encoded by these diverse genes may have similar functions [4].

High impact information on CMVs2gp2

• The mechanisms underlying 2b suppression of RNA silencing are unknown [1].
• In addition, our data indicate that the PTGS suppressor activity is important, but not sufficient, for virulence determination by the 2b protein [5].
• By fusion with the green fluorescent protein, we now show that the CMV 2b protein localizes to the nuclei of tobacco suspension cells and whole plants via an arginine-rich nuclear localization signal, (22)KRRRRR(27) [5].
• We report here that the tomato aspermy cucumovirus 2b protein (Tav2b), when expressed from the unrelated tobacco mosaic tobamovirus (TMV) RNA genome, activates strong host resistance responses to TMV in tobacco which are typical of the gene-for-gene disease resistance mechanism [6].
• The structure and genetic diversity of a California Cucumber mosaic virus (CMV) population was assessed by single-strand conformation polymorphism and nucleotide sequence analyses of genomic regions 2b, CP, MP, and the 3' nontranslated region of RNA3 [7].

Biological context of CMVs2gp2

• Both P1/HC-Pro and 2b reversed PTGS of Nii genes in 271-containing tobacco plants, but failed to reverse TGS of 35S-GUS transgenes in the same plant [3].
• Analysis of various population genetics parameters and distribution of synonymous and nonsynonymous mutations revealed that different coding regions and even different parts of coding regions were under different evolutionary constraints, including a short region of the 2b gene for which evidence suggests possible positive selection [7].
• We found that RNA 2 of the four ilarviruses sequenced to date encodes an additional conserved open reading frame (ORF), 2b, that overlaps the 3' end of the previously known ORF, 2a [2].
• The cucumoviral 2b protein is a viral counterdefence factor that interferes with the establishment of virus-induced gene silencing in plants [8].
• We recently reported the molecular characterization and functional analysis of an overlapping gene 2b encoded by RNA 2 of the Q strain of cucumber mosaic cucumovirus (Q-CMV) [9].

Anatomical context of CMVs2gp2

• This fraction was also enriched in histones, suggesting that the CMV 2b protein associates preferentially with the host cell nucleus [8].
• These results suggested that the 2b protein associates either with the nucleus or cytoskeleton of the host cell [8].
• Notably, the Cucumber mosaic virus 2b protein, shown previously to function predominantly by preventing the long-distance transmission of systemic silencing signals, was a very strong silencing suppressor in the protoplasts [10].

Associations of CMVs2gp2 with chemical compounds

• Further analysis showed that the 2b protein was enriched in a fraction that sedimented through a 2.2 M sucrose cushion [8].
• Subcellular fractionation experiments on CMV-infected tobacco leaf tissue showed that the Fny-CMV 2b protein accumulated within a fraction that sedimented at forces of less than 5000 g and that the 2b protein was solubilized only by treatment with urea or SDS [8].

References