GUS EXPRESSION PATTERNS FROM A TOBACCO YELLOW DWARF VIRUS-BASED EPISOMAL VECTOR

We have constructed a binary vector containing elements of the monopar tite geminivirus, tobacco yellow dwarf virus (TYDV). The vector is des igned to be stably integrated into the plant genome, via Agrobacterium -mediated transfer. Upon expression of the viral replication-associate d protein the TYDV elements are released from the T-DNA and then repli cate episomally. We refer to these released forms as multicopy plant e pisomes (MPE). Tobacco plants (Nicotiana tabacum cv 'Samsun') transfor med with the vector showed MPE release and subsequent episomal replica tion in 6 of 11 of these plants. An MPE vector containing the uidA gen e 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 wh ich could be correlated with MPE replication.