9728547 Berry/Gollnick Amaranth is a dicotyledonous grain plant that uses the highly efficient c4 pathway of photosynthesis. In amaranth, the expression of genes encoding the large subunit (LSU, produced from the plastid-encoded rbcL gene) and small subunit (SSU, produced from nuclear-encoded rbcS genes) of ribulose 1,5-bisphosphate (RuBPCase) is strongly regulated by light and by developmental processes. Previously, it has been shown that very rapid changes in synthesis of the LSU and SSU polypeptides are induced in response to changes in illumination, and that these changes are due to regulation at the translations/level. In addition, alterations in translation from rbcL and RbcS mRNAs are associated with changes in leaf photosynthetic capacity, and appear to occur during various stages of leaf development. The research to be conducted will analyze light-dependent mRNA/protein interactions that occur at the 5' UTR of rbcL mRNA. The light-dependent binding of two 47 kDa proteins and the formation of a slow-migrating gel mobility shift complex to processed rbcL 5'UTR sequences are tightly associated with our observations of light-induced activation of RuBPCase LSU translation. To better understand the role of mRNA/protein interactions in regulating the synthesis of this plastid-encoded photosynthetic polypeptide, the predominant 47 kDa rbcL 5' UTR mRNA binding proteins will be characterized and their associated factors identified. The formation and composition of the slow-migrating rbcL 5' UTR RNA binding complex produced by plastid extracts from light-grown plants will be investigated, as will the fast-migrating complex produced by the dark-plastid extracts. In addition, it will be determined how processing differences in the length of the rbcL 5' UTR prevent or enhance light-dependent protein binding and complex formation. In the long term, the information acquired from these in depth biochemical studies will be used to characterize the kinetic properties of the light-dependent protein/R NA interactions, and to determine the role of the RNA binding proteins using a transgenic C4 dicot system. These investigations will provide novel insights into mechanisms that regulate photosynthetic gene expression at the translational level in the C4 dicot amaranth and other higher plants. In higher plants light serves both as a primary energy source and as an environmental signal that regulates development. Investigations into light-regulated responses in plants are of fundamental importance in determining how factors controlling plant development respond to environmental stimuli. The process of protein translation is an integral part of the overall pathway of gene expression in all organisms. Rapid changes in the translation of specific mRNAs may be a mechanism for adapting to sudden environmental changes that could affect the survival of the organism. In addition to providing unique perspectives about the genetic control of photosynthesis, this basic research with amaranth will aid in its development as an agriculturally important crop for food production and for industry.
