T7 RNA polymerase-directed expression of an antibody fragment transgene in plastids causes a semi-lethal pale-green seedling phenotype.
A T7 promoter-controlled transgene, AbL, encoding a camel single-domain antibody fragment that binds to the model antigen chicken egg-white lysozyme was introduced into the plastid genome of tobacco. AbL expression was activated in the transplastomic line by introducing a nuclear transgene, ST7, encoding a light-regulated plastid-targeted T7RNAP by cross-pollination. The resulting AbL x ST7 progeny seedlings developed a pale-green phenotype and ceased growth soon after germination. High levels of AbL transcripts accumulated in AbL x ST7 seedlings and expression of functional AbL antibody was detected by ELISA. Transplastomic AbL plants were also crossed with nuclear-transformed tobacco plants containing a salicylic acid-inducible transgene encoding a plastid-targeted T7RNAP (PR-T7 transgene). The resulting AbL x PR-T7 progeny were wild-type in appearance but were slow growing and prone to wilting even when provided with adequate water. Although AbL transcription was inducible by treating AbL x PR-T7 leaves with salicylic acid, high levels of T7RNAP-dependent AbL transcripts also accumulated in the absence of induction. However, AbL antibody did not accumulate at levels detectable by immunoblotting or ELISA in AbL x PR-T7 plants despite the fact that total leaf RNA containing AbL transcripts was capable of directing AbL antibody synthesis in an E. coli-derived in vitro translation system.[1]References
- T7 RNA polymerase-directed expression of an antibody fragment transgene in plastids causes a semi-lethal pale-green seedling phenotype. Magee, A.M., Coyne, S., Murphy, D., Horvath, E.M., Medgyesy, P., Kavanagh, T.A. Transgenic Res. (2004) [Pubmed]
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