Abstract
BackgroundIn Raphanus sativus (Japanese radish), strain D8 of cucumber mosaic virus (CMV-D8) establishes a systemic infection and induces mild mosaic on upper, non-inoculated leaves, whereas strain Y of CMV (CMV-Y) causes only a local infection in the inoculated leaves. Here, we further analyzed the specific viral factor(s) of CMV-D8 that is (are) indispensable for systemic infection in Japanese radish.MethodsTo identify which genomic RNA(s) is (are) involved in systemic infection in radish, we carried out a pseudorecombination analysis between CMV-D8 and CMV-Y. With recombination analyses between CMV-D8 and CMV-Y using mutant/recombinant RNA2s, chimeric and point-mutated RNA3s, we identified viral factors that are indispensable for systemic infection.ResultsViral RNA2 and RNA3 of CMV-D8 facilitated efficient virus spread into the upper, non-inoculated plant tissues of radish (cv. Tokinashi), but not those of CMV-Y. Recombinant RNA2s demonstrated that the 2b protein (2b) and the C-terminus of the 2a protein (2a) of CMV-D8 have a crucial role in systemic infection. In addition, we used chimeric and point-mutated RNA3s to that Pro17 and Pro129 in the coat protein (CP) of CMV-D8 are involved in efficient systemic infection and that Ser51 in the 3a protein (3a) of CMV-D8 has positive effects on systemic spread. The results suggested that these viral factors facilitate systemic infection of CMV-D8 in Japanese radish.ConclusionThe C-terminal region of 2a, the entire region of 2b, and supplementary function of either Ser51 in 3a or Pro17/Pro 129 in CP confer systemic infectivity on CMV-D8 in radish. These results further elucidate the complex interaction of viral proteins of CMV to complete systemic infection as a host-specific manner.
Highlights
In Raphanus sativus (Japanese radish), strain D8 of cucumber mosaic virus (CMV-D8) establishes a systemic infection and induces mild mosaic on upper, non-inoculated leaves, whereas strain Y of CMV (CMV-Y) causes only a local infection in the inoculated leaves
CMV-D8 systemically spread in radish In the initial step of this study, we examined the pathogenicity of CMV-D8 and CMV-Y using radish cv
Relative levels of CMV-D8 and CMV-Y in the plants at 10 days post inoculation and 21 dpi was compared in total RNAs extracted from the inoculated and the upper, non-inoculated leaves, respectively, using relative Quantitative reverse transcription polymerase chain reaction (RT-qPCR) targeting CMV RNA2
Summary
In Raphanus sativus (Japanese radish), strain D8 of cucumber mosaic virus (CMV-D8) establishes a systemic infection and induces mild mosaic on upper, non-inoculated leaves, whereas strain Y of CMV (CMV-Y) causes only a local infection in the inoculated leaves. Infecting more than 1200 dicotyledonous and monocotyledonous plant species, cucumber mosaic virus (CMV; genus Cucumovirus, family Bromoviridae) is one of the most important viruses worldwide [10, 27, 30]. Protein 2b, encoded by subgenomic RNA4A from RNA2 is well known as a viral silencing suppressor [21, 24] and is responsible for long-distance viral movement [6, 42] and determining pathogenicity and symptom types [7]. The CP is critical for cellto-cell and systemic movement of the virus, determining pathogenicity, virus accumulation, symptom induction, and vector transmission [19, 23, 26, 29, 33, 43]. Cell-to-cell and long-distance movement of viruses are the most important factor for systemic infection in plants [3]
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