REGULATION OF STORAGE PROTEIN-SYNTHESIS IN CEREAL SEEDS - DEVELOPMENTAL AND NUTRITIONAL ASPECTS

The major seed storage proteins of cereals are deposited in the matura tion phase of endosperm development, starting at 12 days after pollina tion (dap) in maize and continuing up to around 30 dap. Cell type-spec ific expression in the endosperm is conferred by a multicomponent prom oter motif, the endosperm box sequence. Proteins interacting at this m otif include the gene product of the regulatory gene Opaque-2 (O2). O2 encodes a bZIP transcription factor, which is capable of activating i ts target promoters, 22 kD alpha-zein and b-35 in a number of experime ntal systems. Storage protein accumulation, and storage protein promot er activity, are modulated according to available levels of nitrogen ( N). In barley, nitrogen regulation is mediated by the endosperm box vi a interaction of the endosperm and GCN4 motifs. The nitrogen-responsiv e components of the 22 kd zein promoter have been shown to include the O2-binding sites Z1-Z3 but to display N-responsiveness even in the ab sence of O2 protein.