Rapid, high-level expression of biologically active alpha-trichosanthin in transfected plants by an RNA viral vector

alpha-Trichosanthin, a eukaryotic ribosome-inactivating protein from Trichosanthes kirilowii, inhibits the replication of the human immunodeficiency virus (HIV) in vitro. The alpha-trichosanthin gene was placed under the transcriptional control of a tobamovirus subgenomic promoter in a plant RNA viral vector. Two weeks after inoculation, transfected Nicotiana benthamiana plants accumulated alpha-trichosanthin to levels of at least 2% of total soluble protein. The recombinant alpha-trichosanthin was purified and its structural and biological properties were analyzed. The 23-amino acid signal peptide was recognized by N. benthamiana and the processed enzyme caused a concentration-dependent inhibition of protein synthesis in vitro. The high level of heterologous gene expression observed in these studies is due to the unique features of the RNA viral-based transfection system.