COEXPRESSION OF THE MAIZE DELTA-ZEIN AND BETA-ZEIN GENES RESULTS IN STABLE ACCUMULATION OF DELTA-ZEIN IN ENDOPLASMIC RETICULUM-DERIVED PROTEIN BODIES FORMED BY BETA-ZEIN

Zeins, the major seed storage proteins of maize, are of four distinct types: alpha, beta, delta, and gamma. They are synthesized on the roug h endoplasmic reticulum (ER) in a sequential manner and deposited in E R-derived protein bodies. We investigated the potential for producing sulfur-rich beta-zein and delta-zein proteins in leaf and seed tissues by expressing the corresponding genes in a constitutive manner in tra nsgenic tobacco. The delta-zein and beta-zein, when synthesized indivi dually, were stable in the vegetative tissues and were deposited in un ique, zein-specific ER-derived protein bodies. Coexpression of delta-z ein and beta-zein genes, however, showed that delta-zein was colocaliz ed in beta-zein-containing protein bodies and that the level of delta- zein was fivefold higher in delta-/beta-zein plants than in delta-zein plants. We conclude that delta-zein interacts with beta-zein and that the interaction has a stabilizing effect on delta-zein.