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| The Cb7 isolate of Cucumber mosaic virus (CMV) induces severe leaf distortion on Nicotiana tabacum in contrast to CMV-Fny that causes systemic mosaic in this host. It was found that N. tabacum plants infected with the reassortant, a combination of transcripts derived from cDNAs of CMV-Fny RNA1 and 2 (F1 and F2) and of CMV-Cb7 RNA3 (F12C3), displayed severe leaf distortion symptoms characteristic of the wild-type Cb7 infection, indicating that genomic RNA3 had a distinctive role in the determination of the symptom. An exchange of the fragment containing CP gene between Cb7 and Fny constructed two chimeric RNA3s: CFB, including CP gene of Fny, and FCB, including CP gene of Cb7. Each chimera mixed with F1 and F2 was inoculated onto N. tabacum. The F12CFB-infected plants expressed systemic mosaic symptoms, while the F12FCB-infected ones showed severe leaf distortion symptoms. The results suggested that the genetic determinant of the severe leaf distortion symptom showing on N. tabacum was exclusively associated with the fragment containing CP gene in the Cb7 genome. Accumulation of CMV RNAs in the systemic leaves of N. tabacum plants infected with the reassortant was determined using Northern blotting. The results showed that the accumulation of subgenomic RNA4 of F12FCB was significantly higher than that of F12CFB and Fny, as a control, and the amounts of RNA4 of F12CFB were equivalent to those of Fny. Therefore, it had been inferred that the high amounts of viral subgenomic RNA4, presenting high accumulation of CP, might be responsible for the severe leaf distortion symptom expression on N. tabacum. |
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| Keywords:Severe leaf distortion Cucumber mosaic virus Reassortment CP gene |
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