Molecular mechanisms regulating the synthesis of storage proteins in maize endosperm

During the development of maize seed large amounts of protein are synthesized and deposited in the endosperm. The largest proportion of this protein consists of the storage protein fraction called zein, which may account for as much as 60% of the total protein. A large number of environmental and genetic factors are known to affect the synthesis of zein proteins. For example, it is well documented that the application of nitrogen fertilizer greatly enhances synthesis of the zein fraction. On the other hand, endosperm mutations such as opaque‐2 and floury‐2 reduce the synthesis of these proteins by 50% or more. The biochemical mechanisms by which these factors alter storage protein synthesis have not been identified primarily because little is known regarding the molecular basis for zein synthesis. Our studies have revealed the role of two translational mechanisms involved in enhanced storage protein synthesis in maize endosperm. One of these involves preferential initiation of zein mRNAs, and the other involves cotranslational processing of the zein polypeptides as they enter the lumen of the endoplasmic reticulum.