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https://hdl.handle.net/2142/85040
Description
Title
Functional Genomics of Nitrogen Use in Maize
Author(s)
Church, Jeffrey Brian
Issue Date
2008
Doctoral Committee Chair(s)
Stephen Moose
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Language
eng
Abstract
Maize cultivars vary widely in their ability to translate nitrogen (N) accumulated during growth into grain yield. Little is known about what determines this capacity, termed N-utilization efficiency (NUtE) in agronomic studies. However, recent investigations have implicated the variation in how carbon (C) and N are partitioned within source tissues, where they are either utilized immediately for growth, or stored in alternative forms more readily catabolised when N is limiting. In order to explore the molecular basis for this variation we compared B73 to an inbred of Illinois High Protein (IHP), a genotype with high N uptake and accumulation, but poor NUtE due to selection for grain protein concentration. We compared IHP to B73 in four greenhouse experiments that exposed plants and excised leaves to varying N-deficient and N-sufficient conditions. Plants were grown to the 2nd and 8th leaf stages, and analyses were conducted on growth and major metabolic, enzymatic and transcriptional components of leaf resource management. We confirmed lower biomass and photosynthetic responses to N in IHP, coupled with greater N uptake and an enhanced ability to accumulate amino acids, even at lower internal concentrations of N. Transcriptional analyses revealed widespread regulation of the N-assimilation genes, which responded to N more strongly in IHP and acted coordinately to funnel C toward asparagine and away from malate, a C4 carrier and TCA intermediate. B73 showed a greater preference for malate synthesis at the transcript abundance and metabolite levels, although both lines responded to N with greater chlorophyll and amino-N, increased expression of amino acid genes and stromal enzymes, and altered carbon balance in the form of lower malate-to-aspartate ratios. We propose that selection for grain protein concentration in IHP indirectly established several early developmental and molecular behaviors that act coordinately within the leaves to partition C and N away from growth and into resources best suited for N storage and remobilization. The results of our studies shed new light on how transcriptional responses in particular can be utilized to moderate the partitioning of leaf resources into storage assimilates and maximize NUtE in all cropping systems.
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