The Maize y-Zein Sequesters a-Zein and Stabilizes Its Accumulation in Protein Bodíes of Transgenic Tobacco Endosperm

Zeins are seed storage proteins that form accretions called protein bodies in the rough endoplasmic reticulum of maize endosperm cells. Four types of zeins, a, p, y , and 6, aggregate in a distinctive spatial pattern within the protein body. We created transgenic tobacco plants expressing a-zein, y-zein, or both to examine the interactions between these proteins leading to the formation of protein bodies in the endosperm. Whereas y-zein accumulated in seeds of these plants, stable accumulation of a-zein required simultaneous synthesis of y-zein. The zein proteins formed accretions in the endoplasmic reticulum similar to those in maize endosperm. Protein bodies were also found in protein storage vacuoles. The accumulation of both types of zeins peaked early in development and declined during maturation. Even in the presente of y-zein, there was a turnover of a-zein, suggesting that the interaction between the two proteins might be transitory. We suggest that y-zein plays an important role in protein body formation and demonstrate the utility of tobacco for studying interactions between different zeins.