Lysine-rich c-zeins are secreted in transgenic Arabidopsis plants

We have previously shown that the maize (Zea mays L.) storage prolamine γ-zein, accumulates in endoplasmic reticulum-derived protein bodies in transgenic plants of Arabidopsis thaliana (L.) ecotype R+P. The retention of γ-zein in the endoplasmic reticulum was found to be mediated by structural features contained in the polypeptide, an N-terminal proline-rich and a C-terminal cysteine-rich domain which were necessary for the correct retention and assembly of γ-zein within protein bodies (M.I. Geli et al., 1994, Plant Cell 6: 1911–1922). In the present work we incorporated in the γ-zein gene lysine-rich coding sequences which were positioned after the N-terminal proline-rich domain and at five amino-acid residues from the C-terminus. The targeting of lysine-rich γ-zeins was analyzed by expression of chimeric genes regulated by the cauliflower mosaic virus (CaMV) 35S promoter in transgenic Arabidopsis plants. The lysine-rich γ-zeins were detected by immunoblotting and we found that these proteins were modified post-translationally to reach their mature form. Subcellular fractionation and immunocytochemical studies demonstrated that glycosylated lysine-rich γ-zeins were secreted to the cell wall of transgenic Arabidopsis leaf cells. Received: 9 May 1997 / Accepted: 31 October 1997