SYNTHESIS OF A FUNCTIONAL ANTIPHYTOCHROME SINGLE-CHAIN-FV PROTEIN IN TRANSGENIC TOBACCO

We have expressed a synthetic gene that encodes an antigen-binding single-chain F(v) protein (scF(v)) in transgenic tobacco plants. The scF(v) gene was created by polymerase chain reaction (PCR) amplification of the variable domain coding regions from a mouse monoclonal hybridoma cell line. The monoclonal cell line secretes an IgG1 antibody that binds to the plant regulatory photoreceptor protein, phytochrome. The cloned scF(v) gene was expressed initially in Escherichia coli and shown to produce a 28 kD, phytochrome-binding scF(v) protein. Transgenic tobacco plants expressing the scF(v) gene were also found to produce a functional scF(v) protein, and seeds from transgenic R1 progeny displayed aberrant phytochrome-dependent germination. The scF(v) from transgenic tobacco could be isolated, to near homogeneity, by a single phytochrome-Sepharose affinity chromatography step.