Knockdown expression of a MYB-related transcription factor gene, OsMYBS2, enhances production of recombinant proteins in rice suspension cells

Background: Transgenic plant suspension cells show economic potential for the production of valuable bioproducts. The sugar starvation-inducible rice αAmy3 promoter, together with its signal peptide, is widely applied to produce recombinant proteins in rice suspension cells. The OsMYBS2 transcription factor was shown recently to reduce activation of the αAmy3 promoter by competing for the binding site of the TA box of the αAmy3 promoter with the potent OsMYBS1 activator. In this study, rice suspension cells were genetically engineered to silence OsMYBS2 to enhance the production of recombinant proteins. Results: The mouse granulocyte–macrophage colony-stimulating factor (mGM-CSF) gene was controlled by the αAmy3 promoter and expressed in OsMYBS2-silenced transgenic rice suspension cells. Transcript levels of the endogenous αAmy3 and the transgene mGM-CSF were increased in the OsMYBS2-silenced suspension cells. The highest yield of recombinant mGM-CSF protein attained in the OsMYBS2-silenced transgenic suspension cells was 69.8 µg/mL, which is 2.5-fold that of non-silenced control cells. The yield of recombinant mGM-CSF was further increased to 118.8 µg/mL in cultured cells derived from homozygous F₅ seeds, which was 5.1 times higher than that of the control suspension cell line. Conclusions: Our results demonstrate that knockdown of the transcription factor gene OsMYBS2 increased the activity of the αAmy3 promoter and improved the yield of recombinant proteins secreted in rice cell suspension cultures.