Nitrogen Signaling By Glutamate Synthesized By GDH Transgenes in the Cytoplasm Improves Crop Growth and Reduced Flavotoxin Contamination

New crop plants suited to growth in semi-arid environments will be fundamental to the future of agriculture. The interactions between nitrogen supply and water availability that determine yield and quality in crops grown in semi-arid environments are being elucidated. Maize (Zea mays L.) and other crop plants have altered transcript and metabolic profiles caused by in planta expression of the bacterial glutamate dehydrogenase (EC 1.4.1.2), a modified gdhA. The change in glutamate concentration in the cytoplasmic pool has profound effects on plant metabolisms. The metabolic changes resulted in phenotypic changes that included increases in mean plant biomass production in dry soils, tolerance to the herbicide phosphinothricin, tolerance to both severe and mild water deficit. Leaves and grain had higher nutritional value and higher yield indicating improved NUE and WUE. Comparisons of transgenic and non transgenic maize under drip irrigation showed a 11% increase in WUE and 9% increase in NUE across a range of water delivery rates. The variation caused by the transgene was greater than that found in a set of maize and soybean germplasm tested. Resistance to rotting necrotrophs including carcinogenic Aspergillus flavus contaminations was noted. Sporulation of A. flavus was inhibited and the abundance of 747 fungal and 395 maize grain transcripts were altered suggesting the GDH maize was not supporting normal fungal growth because of metabolic and compositional alterations. Cancer incidences due to toxin contamination can potentially be reduced by 50% by GDH. There were about 283 metabolites in roots, 98 metabolites in leaves and 56 metabolites in grain that changed abundances including some increases in nutritionally valuable amino acids. Among the transcripts reduced in abundance by GDH 7 were significantly associated with resistance to infection by A. flavus based on an association map. The altered transcripts, metabolites and proteins provided biomarkers for these valuable traits. See US patents 5,998,700; 6,329,573; and 8,383,887.