A modified 10 kD zein protein produces two morphologically distinct protein bodies in transgenic tobacco

The 10 kD zein protein contains an N-terminal signal peptide that directs t he protein into the endoplasmic reticulum (ER) of developing corn seeds. Su bsequent to signal peptide removal, the mature protein is folded into its t ertiary conformation and deposited into protein bodies. In transgenic tobac co leaves, the 10 kD zein protein accumulates and forms novel ER derived pr otein bodies (S. Bagga, H. Adams, F. Rodriquez, J.D. Kemp, C. Sengupta-Gopa lan, Coexpression of the maize F-zein and p-zein genes results in stable ac cumulation of delta-zein in endoplasmic reticulum-derived protein bodies fo rmed by beta-zein, The Plant Cell 9 (1997) 1683-1696). In this study, the a mino acid sequence of the 10 kD zein signal peptide was modified to determi ne the effect on cleavage and accumulation patterns. The modified zein gene was constitutively expressed in tobacco where its protein accumulates in n ovel protein bodies in leaves. Amino acid sequencing of the accumulated pro tein indicates that the cleavage site for the signal peptide was altered so that the mature protein includes three additional amino acids on the N-ter minus. Electron microscopy (EM) analysis of leaves from transgenic plants c ontaining the modified gene indicates the presence of two morphologically d istinct protein bodies. Furthermore, immunolocalization analysis shows that the modified protein is localized in both types of protein bodies, which a re described as spherical and aggregate in this report. This is in contrast to the accumulation of unmodified 10 kD zein protein in transgenic leaves where only spherical protein bodies are observed. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.