Transplastomic plants are a system of choice for the mass production of biopharmaceuticals due to the polyploidy of the plastid genome and the low risk of pollen-mediated outcrossing because of maternal inheritance. However, as field-grown plants, they can suffer contamination by agrochemicals and fertilizers, as well as fluctuations in yield due to climatic changes and infections. Tissue-type plasminogen activator (tPA), a protein used to treat heart attacks, converts plasminogen into plasmine, which digests fibrin and induces the dissolution of fibrin clots. Recently, we obtained transplastomic tobacco plants carrying the K2S gene encoding truncated human tPA (reteplase) with improved biological activity, and confirmed the presence of the target protein in the transgenic plant leaves. Considering the advantages of plant cell cultures for biopharmaceutical production, we established a cell line derived from the K2S tobacco plants. The active form of reteplase was quantified in cultures grown in light or darkness, with production 3-fold higher in light.

As because the plant plastid genome is highly polyploid, the transformation of chloroplasts permits the introduction of thousands of copies of foreign genes per plant cell and generates extraordinarily high levels of recombinant protein. Human tissue-type plasminogen activator is one of the most important pharmaceutical proteins involved in the breakdown of blood clots in brain and heart blood vessels. We report the introduction and expression of the truncated human tissue plasminogen activator (K2S) gene in tobacco chloroplasts. The K2S-containing vector pKCZK2S was successfully transferred to tobacco plastomes using the biolistic delivery procedure. Transplastomic plants were selected on RMOP medium containing spectinomycin (500 mg/l). In order to achieve homoplasmy, several rounds of selection and regeneration were performed. The presence, site-specific integration, homoplasmy, expression and activity assay of the transgene were confirmed in the transplastomic plants by PCR, Southern-blot, RT-PCR, SDS-PAGE, ELISA, Dot-blot, Western-blot and zymography analysis. Our results show that the tissue plasminogen activator (K2S form) protein to be expressed in tobacco chloroplasts in active form.

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Tissue plasminogen activator (tPA) as a serine protease with 72 kD molecular mass and 527 amino acids plays an important role in the fibrinolytic system and the dissolution of fibrin clots in human body. The collective production of this drug in plants such as cucumber, one of the most important vegetables in the world, could reduce its production costs. In this study, after scrutiny of the appropriate regeneration of cucumber plant (Isfahan variety) on MS medium with naphthalene acetic acid hormone (NAA; 0/1 mg L⁻¹) and benzyl amino purine hormone (BAP; 3 mg L⁻¹) hormones, the cloned human tPA gene under the CaMV 35S promoter and NOS terminator into pBI121 plasmid was transferred into cotyledon explants by Agrobacterium tumefaciens strain LBA4404. Subsequent to the regeneration of inoculated explants on the selective medium, the persistence of tPA gene in recombinant plants was confirmed by polymerase chain reaction (PCR) with specific primers. To evaluate the tPA gene expression in transgenic plants, RNA was extracted and the tPA gene transcription was confirmed by reverse-transcription (RT) PCR. Followed the extraction of protein from the leaves of transgenic plants, the presence of tPA protein was confirmed by dot blot and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) analysis in order to survey the production of recombinant tPA protein. The enzyme-linked immunosorbent assay (ELISA) test was used for recombinant tPA protein level in transgenic cucumber plants. It was counted between 0.8 and 1%, and based on this, it was concluded that the presence of three expressions of regulatory factors (CaMV 35S, Kozak, NOS) and KDEL signal in the construct caused the increase of the tPA gene expression in cucumber plants.

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