Facile assessment of cDNA constructs for expression of functional antibodies in plants using the potato virus X vector

Antibodies have been expressed in plants to confer novel traits such as vir us resistance or altered phenotype. However, not every antibody is suitable for plant expression, and successful intracellular expression of antibody fragments depends primarily on their amino acid sequence in a way that is a s yet unpredictable. Therefore it is desirable to assess different construc ts before embarking on the production of transgenic plants. We have used a transient expression system based on potato virus X to compare different cD NA constructs for expression and stability of antibody variable gene fragme nts in plants. Constructs contained an anti-plant enzyme (granule-bound sta rch synthase I) scFv sequence derived from a naive phage display library to gether with different combinations of sequences encoding the human IgG kapp a constant domain, a murine IgG secretory signal sequence, or the endoplasm ic reticulum retention signal peptide KDEL. The results obtained with the p otato virus X vector correlated with those from Agrobacterium-mediated stab le transformation of potato. The best expression levels were obtained by in corporating sequences that target scFv to the lumen of the endoplasmic reti culum and the secretory pathway. The anti-enzyme scFv retained activity dur ing storage of potato tubers for more than five months. The results demonst rate the utility of the potato virus X vector for the analysis and comparis on of many scFv with different epitope specificities or sequence modificati ons. Evaluation of scFv by transient expression from the PVX vector should aid progress in selection of functional scFv for applications in plant biot echnology.