GUS expression patterns from a tobacco yellow dwarf virus-based episomal vector

We have constructed a binary vector containing elements of the monopartite geminivirus, tobacco yellow dwarf virus (TYDV). The vector is designed to be stably integrated into the plant genome, via Agrobacterium-mediated transfer. Upon expression of the viral replication-associated protein the TYDV elements are released from the T-DNA and then replicate episomally. We refer to these released forms as multicopy plant episomes (MPE). Tobacco plants (Nicotiana tabacum cv 'Samsun') transformed with the vector showed MPE release and subsequent episomal replication in 6 of 11 of these plants. An MPE vector containing the uidA gene faithfully replicated and maintained the reporter gene, even though the construct was considerably larger than the wild-type TYDV genome. Histochemical staining revealed a speckled GUS expression phenotype which could be correlated with MPE replication.