Expression of α-1,6-fucosyltransferase (FUT8) in rice grain and immunogenicity evaluation of plant-specific glycans

- We studied the plant-specific glycan type and composition in rice endosperm cell.
- We analyzed the α-1,3-fucose contents of the glycoprotein produced from rice endosperm and leaf cells, and found that those glycans were much lower in endosperm than that in leaf cells.
- The expression of FUT8 gene in rice endosperm cell not only introduced human-specific α-1,6-fucose, but also reduced the α-1,3-fucose content.
- The immunogenicities studies revealed that no significant difference was found in antibody concentration among OsrAAT, mgOsrAAT and hAAT.
- This work updates the concept of immunogenicity of plant-specific glycans.

Rice seed is a cost-effective bioreactor for the large-scale production of pharmaceuticals. However, convincing evidence of the immunogenicity of plant-specific glycans is still limited although plant-specific glycans are considered potential allergic antigens. In the present study, we found that the α-1,3-fucose content of the glycoprotein produced from rice seed was much lower than that in leaf, and conversely, a higher β-1,2-xylose content was detected in seed than that in leaf. We detected the α-1,6-fucose content in the glutelin and recombinant human α1-antitrypsin (OsrAAT). The further results in a line containing AAT and FUT8 genes indicated that the α-1,6-fucose content of modified glycosylated recombinant α1-antitrypsin (mgOsrAAT) was 38.4%, while glutelin was only 6.8%. Interestingly, the α-1,3-fucose content of mgOsrAAT was significantly reduced by 59.8% compared with that of OsrAAT. Furthermore, we assessed the immunogenicity of OsrAAT, mgOsrAAT and human α1-antitrypsin (hAAT) using an animal system. The PCA results indicated no significant differences in the IgG, IgM and IgE titers among OsrAAT, mgOsrAAT and hAAT. Further studies revealed that those antibodies were mainly from α-1,3-fucose, but not from β-1,2-xylose, indicating that α-1,3-fucose was the major immunogenic resource. Our results demonstrated that α-1,3-fucose contents in seed proteins was much less than that of leaf, and could not be a plant-specific glycan because it also exists in human proteins.