Active RNA silencing at low temperature indicates distinct pathways for antisense-mediated gene-silencing in potato.

Previously, it was shown that low temperature (<or= 15 degrees C) inhibits RNA silencing-mediated defence by the control of siRNA generation. In contrast, we have found nine antisense potato lines out of 24 in which RNA silencing was not inhibited at low temperature. In these lines, the extent of endogenous repression varied in leaves and was found to be different in roots and tubers. In order to address the contribution of gene dosage and repetitive structure of the transgene loci to the temperature dependence/independence of antisense-mediated gene-silencing DNA gel blot analysis was performed. Interestingly, none of the studied features correlated with the observed silencing effect. In addition, the insertion of vector backbone sequences into the potato genome did not influence the temperature dependence. RNA-directed DNA methylation was detected in the majority of antisense lines, however, it was also independent of the type of RNA silencing. Thus, it is feasible that chromosomal flanking sequences or the chromatin structure surrounding the insertion determine which silencing pathway is activated.