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

Abstract

The 10 kD zein protein contains an N-terminal signal peptide that directs the protein into the endoplasmic reticulum (ER) of developing corn seeds. Subsequent to signal peptide removal, the mature protein is folded into its tertiary conformation and deposited into protein bodies. In transgenic tobacco leaves, the 10 kD zein protein accumulates and forms novel ER derived protein bodies (S. Bagga, H. Adams, F. Rodriquez, J.D. Kemp, C. Sengupta-Gopalan, Coexpression of the maize δ-zein and β-zein genes results in stable accumulation of δ-zein in endoplasmic reticulum-derived protein bodies formed by β-zein, The Plant Cell 9 (1997) 1683–1696). In this study, the amino acid sequence of the 10 kD zein signal peptide was modified to determine the effect on cleavage and accumulation patterns. The modified zein gene was constitutively expressed in tobacco where its protein accumulates in novel protein bodies in leaves. Amino acid sequencing of the accumulated protein indicates that the cleavage site for the signal peptide was altered so that the mature protein includes three additional amino acids on the N-terminus. Electron microscopy (EM) analysis of leaves from transgenic plants containing the modified gene indicates the presence of two morphologically distinct protein bodies. Furthermore, immunolocalization analysis shows that the modified protein is localized in both types of protein bodies, which are 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.