Plant, Animal & Microbe Genomes X Conference Plant, Animal & Microbe Genomes X ConferenceJanuary 12-16, 2002
Town & Country Convention Center
San Diego, CA
Poster: Genome Sequencing & ESTs
In the post-genome sequence era the determination of gene function(s) and relationships to pathways will be the focus. Multi-parallel analysis of mRNA abundance and their protein products will suggest functions but not direct information on biological function. The multiplicity of gene interactions and metabolic networks changes engineered by mutation are not always predictable, and many changes are cryptic. Metabolic profiling can link phenotype to biochemistry. Glutamate (and pyruvate) are the nodal compounds in the network of reactions involved in plant metabolism. Genetic modification of nitrogen metabolism via the bacterial glutamate dehydrogenase (GDH) favorably alters microbe and plant growth and metabolism. Damage caused by the Liberty herbicide, a glutamine synthetase (GS) inhibitor, was less pronounced in gdhA plants suggesting that the introduced GDH can replace some GS activity and act synergistically with the Liberty-link genes. Leaf area duration and grain biomass production was often increased in gdhA transgenic plants grown under controlled conditions and in the field particularly during water deficit. Total free amino acids and total carbohydrate were increased in gdhA plants grown in the greenhouse suggesting that both nitrogen and carbon metabolisms were altered in source tissues. The additional soluble compounds may cause the drought tolerance. The transgene used in this study increased glutamate synthesis by 5-10% judged by 15N labeling. In MS analysis of metabolites between 100-961 d using an ion cyclotron showed there were 315 metabolites in the root extracts and 58 metabolites in the leaf extracts that were observed to have changed from over 4,000 different metabolites detected. Amino acids, sugars and lipid pool sizes were altered. We show that the modifications in transgenic plants resulted less from increased efficiency of nitrogen assimilation than by altered metabolic node fluxes that result from modest amount of glutamate generation in the cytoplasm. The transgene directed metabolic profile produced higher concentration of compatible solutes that provide water-deficit tolerance to the plants.