ABSTRACT
The expression of translatable sequences of either one of the two Andean potato mottle virus (APMoV) coat protein (CP) genes (CP22 and CP42) and of the nontranslatable sequence of CP42 in transgenic tobacco provided protection against APMoV. Resistance was mediated by CP transgene RNAs rather than the protein, as an inverse correlation between resistance and the accumulation levels of CPs transgene mRNAs was observed. These data indicated that a post-transcriptional gene silencing (PTGS) mechanism is likely involved in the APMoV CP RNA-mediated protection. Moreover, the HindIII-AccI restriction pattern of the CP22 transgene was different in susceptible and resistant transgenic plants, suggesting the involvement of methylation in PTGS. Southern blot experiments also revealed that CPs transgene insertion loci and organisation in the plant genome may play a role in determining the degree of protection.
ABSTRACT
Nicotiana tabacum plants were transformed with the 3'-untranslated region of the Andean Potato Mottle Virus (APMoV) genome RNA-2. Three strategies were used: the introduction of this region in sense and in antisense orientation and of a fragment comprising the entire 3'-untranslated region from RNA-2 and part of the CP22 coat protein sequence. The transgenic lines were inoculated with the virus and different responses were observed, ranging from susceptibility to APMoV to complete immunity to virus infection, in which neither the virion nor viral RNA was detected in the inoculated leaf and leaves that emerged after inoculation. The R1 progeny from different R0 lines also showed an array of virus resistance phenotypes, which was not correlated with the zygotic state of the transgene. Resistance was positively correlated with low levels of transgene mRNA accumulation, indicating a co-suppression-mediated mechanism towards the transgenic transcripts and APMoV viral RNA.