P0404
Modulating Nitrogen Flux in Sorghum and Wheat

Pamela A. Pena , University of Nebraska-Lincoln, Lincoln, NE
Truyen Quach , University of Nebraska-Lincoln, Lincoln, NE
Shirley Sato , University of Nebraska-Lincoln, Lincoln, NE
Natalya Nersesian , University of Nebraska-Lincoln, Lincoln, NE
Zhengxiang Ge , University of Nebraska-Lincoln, Lincoln, NE
Soundararajan Madhavan , University of Nebraska-Lincoln, Lincoln, NE
Thomas E Clemente , University of Nebraska-Lincoln, Lincoln, NE
Nitrogen is one of the most important nutrients and it is essential for plant growth and development. Cereal crop species such as sorghum and wheat require inputs of nitrogenous fertilizers in order to maximize yield and plant productivity. Since nitrogen assimilation and remobilization require the presence of carbon skeletons, the modulation of carbon skeleton production has been explored as a strategy to enhance nitrogen use efficiency in plants. To this end we evaluated a transcription factor approach in which the maize Dof1,  (ZmDof1) was expressed in both wheat and sorghum under the control of two different promoters: a constitutive UBI4 promoter from sugarcane and tissue specific regulated via the maize rbcS1 promoter. The activity of the primary target of Dof1, phosphoenol pyruvate carboxylase (PEPC) was increased in transgenic plants overexpressing Dof1.  Moreover, a transcript profile of wheat plants overexpressing UBI4::ZmDof1 indicated the upregulation of 137 transcripts and downregulation of 94 transcripts. Evaluations for nitrogen use efficiency under hydroponic conditions in wheat indicated that the use of a strong constitutive promoter UBI4 results in plants with a stunted and abnormal phenotype, whereas the use of rbcS1 promoter which drives a reduced level of expression in vegetative tissues of Dof1, modulates carbon metabolic processes that can result in increased biomass and nitrogen use efficiency. Similar phenotypes were observed in evaluations for nitrogen use efficiency under field conditions including increased height and increased yield particularly under low nitrogen conditions in wheat plants overexpressing rbcS1::ZmDof1. Moreover, the stunted and abnormal phenotype was also observed in sorghum plants overexpressing UBI4::ZmDof1. However, no changes in biomass were observed when the expression of Dof1 was driven by the rbcS1 promoter. Furthermore, as a means to complement the transcription factor strategy for NUE we have also explored expression of the rice glutamine synthetase and barley alanine aminotransferase in the two commodity crops.
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