Dissecting the Role of the Individual Cytosolic Glutamine Synthetase Gene Family in Zea Mays

Maize (Zea mays L.) plants possess two main forms of glutamine synthetase: the cytosolic (GS1) and plastidic (GS2) forms. In maize, the GS1 forms are encoded by at least five genes (Gln1-1-7 Gln1-5) which are differentially expressed. This project characterized the mutants generated by the insertion of Mutatortransposable elements in various Gln1 genes in order to assess their individual function. Sequencing analysis of previously identified maize lines carrying Mutator insertions within individual Gln1 genes revealed that the Mutator element had transposed into exon 8 of the Gin1-3 gene, and introns 7 and 8 of the Gln1-4 and Gin1-5 genes respectiyely. Phenotypic examination of the various mutant lines during senescence showed that gln1 mutants generally displayed an accelerated rate of leaf yellowing when compared to the rate in the wild type 873 line. Homozygous gln1 mutants produced significantly fewer kernels, which were of lower weight than control 873. Enzymatic characterization of GS in leaves showed that GS1 activity was reduced in the gln1 mutants when compared to the wild type. Transcript analysis suggested that individual Gln1 genes were unable to compensate, via over expression, for other gin1 genes, a result which suggests that the various Gln1 genes are nonredundant. The collated results suggest a role of the Gln1 gene product in regulating the onset of nitrogen remobilization and grain filling through the interaction of the carbon and nitrogen metabolic pathways. Further work is proposed to test this hypothesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo