The Coat Protein Gene is Essential for the Systemic Infection of Cucumber Mosaic Virus in Cucumis figarei at a High Temerature.

Abstract

Systemic infection of cucumber mosaic virus (CMV) in Cucumis figarei at high temperature was investigated using reassortants and chimeric RNAs. Three CMV strains of pepo-, SO-, MY17- and Y-CMV were used: pepo-, SO- and MY17-CMV systemically infected C. figarei at 36°C, whereas Y-CMV did not as previously described. Inoculation with in vitro transcripts from biologically active cDNA clones of Y-CMV and pepo-CMV RNAs 1, 2 and 3 indicated that only the inocula containing pepo-CMV RNA 3 induced systemic infection at 36°C, suggesting that the resistance against systemic infection by Y-CMV and its breakage by pepo-CMV were mapped to CMV RNA 3. Inoculation with transcripts from the cDNA clones of Y-CMV RNAs 1, 2 and RNA 3 of SO-CMV or MY17-CMV provoked systemic infection at high temperature, indicating that the systemic infection by SO-CMV or MY17-CMV was also mapped to RNA 3. Analysis with chimeras constructed between cDNA clones of Y-CMV and pepo-CMV RNA 3 showed that the resistance and resistance breakage were mapped to the coat protein gene on CMV RNA 3. Comparison of the nucleotide sequence of pepo-, SO- and MY17-CMV RNA 3 with that of Y-CMV RNA 3 revealed that the coat protein of Y-CMV differs from those of pepo-, SO- and MY17-CMV in four amino acids at positions 17 (Leu to Pro), 25 (Ser to Pro), 28 (Ser to Ala) and 129 (Ser to Pro). These results suggested that all or some of the four amino acids play an important role in determining long-distance movement of CMV in C. figarei at a high temperature.