| Previous studies demonstrated that the capsid protein (CP) and RNA of Potato Virus X (PVX) accumulate within chloroplasts of transgenic potato plants carrying the tandem 8kD and CP genes of the virus. To elucidate the mechanism(s) of this RNA translocation, transgenic tobacco plants carrying variations of the 8kD-CP construct were produced. Subsequent RT-PCR analyses of total chloroplastic RNA, not only authenticated the RNA translocation event, but also suggested an interesting mechanism for it. Contrary to the proposed hypothesis, transcripts of the constructs with either the 8kD protein or the CP knocked out were shown to successfully enter chloroplasts. The data suggested that neither the 8kD protein nor the CP, otherwise known to mediate cell-to-cell transport of PVX RNA, were responsible for the observed RNA translocation into chloroplasts. Furthermore, it was postulated that a particular sequence within the region (possibly the IRBS of CP), along with host factor(s), may act as an "RNA tractor" into chloroplasts. |
