Present address: Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA.
A protease activity–depleted environment for heterologous proteins migrating towards the leaf cell apoplast
Article first published online: 4 SEP 2011
© 2011 The Authors. Plant Biotechnology Journal © 2011 Society for Experimental Biology, Association of Applied Biologists and Blackwell Publishing Ltd
Plant Biotechnology Journal
Volume 10, Issue 1, pages 83–94, January 2012
How to Cite
Goulet, C., Khalf, M., Sainsbury, F., D’Aoust, M.-A. and Michaud, D. (2012), A protease activity–depleted environment for heterologous proteins migrating towards the leaf cell apoplast. Plant Biotechnology Journal, 10: 83–94. doi: 10.1111/j.1467-7652.2011.00643.x
- Issue published online: 6 DEC 2011
- Article first published online: 4 SEP 2011
- Received 17 February 2011; revised 22 June 2011; accepted 28 June 2011.
- cell secretory pathway;
- leaf apoplast proteome;
- molecular farming;
- Nicotiana benthamiana;
- protease inhibitors;
- recombinant proteins;
- transient expression
Recombinant proteins face major constraints along the plant cell secretory pathway, including proteolytic processing compromising their structural integrity. Here, we demonstrate the potential of protease inhibitors as in situ stabilizing agents for recombinant proteins migrating towards the leaf apoplast. Genomic data for Arabidopsis, rice and Nicotiana spp. were assessed to determine the relative incidence of protease families in the cell secretory pathway. Transient expression assays with the model platform Nicotiana benthamiana were then performed to test the efficiency of protease inhibitors in stabilizing proteins targeted to the apoplast. Current genomic data suggest the occurrence of proteases from several families along the secretory pathway, including A1 and A22 Asp proteases; C1A and C13 Cys proteases; and S1, S8 and S10 Ser proteases. In vitro protease assays confirmed the presence of various proteases in N. benthamiana leaves, notably pointing to the deposition of A1- and S1-type activities preferentially in the apoplast. Accordingly, transient expression and secretion of the A1/S1 protease inhibitor, tomato cathepsin D inhibitor (SlCDI), negatively altered A1 and S1 protease activities in this cell compartment, while increasing the leaf apoplast protein content by ∼45% and improving the accumulation of a murine diagnostic antibody, C5-1, co-secreted in the apoplast. SlCYS9, an inhibitor of C1A and C13 Cys proteases, had no impact on the apoplast proteases and protein content, but stabilized C5-1 in planta, presumably upstream in the secretory pathway. These data confirm, overall, the potential of protease inhibitors for the in situ protection of recombinant proteins along the plant cell secretory pathway.