title: Nitrogen assimilation system in maize is regulated by developmental and tissue-specific mechanisms.
abstract: We found metabolites, enzyme activities and enzyme transcript abundances vary significantly across the maize lifecycle, but weak correlation exists between the three groups. We identified putative genes regulating nitrate assimilation. Progress in improving nitrogen (N) use efficiency (NUE) of crop plants has been hampered by the complexity of the N uptake and utilisation systems. To understand this complexity we measured the activities of seven enzymes and ten metabolites related to N metabolism in the leaf and root tissues of Gaspe Flint maize plants grown in 0.5 or 2.5 mM NO3 (-) throughout the lifecycle. The amino acids had remarkably similar profiles across the lifecycle except for transient responses, which only appeared in the leaves for aspartate or in the roots for asparagine, serine and glycine. The activities of the enzymes for N assimilation were also coordinated to a certain degree, most noticeably with a peak in root activity late in the lifecycle, but with wide variation in the activity levels over the course of development. We analysed the transcriptional data for gene sets encoding the measured enzymes and found that, unlike the enzyme activities, transcript levels of the corresponding genes did not exhibit the same coordination across the lifecycle and were only weakly correlated with the levels of various amino acids or individual enzyme activities. We identified gene sets which were correlated with the enzyme activity profiles, including seven genes located within previously known quantitative trait loci for enzyme activities and hypothesise that these genes are important for the regulation of enzyme activities. This work provides insights into the complexity of the N assimilation system throughout development and identifies candidate regulatory genes, which warrant further investigation in efforts to improve NUE in crop plants.
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.
authors: Darren
authors: D
authors: Plett
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.
authors: Luke
authors: L
authors: Holtham
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.
authors: Ute
authors: U
authors: Baumann
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.
authors: Elena
authors: E
authors: Kalashyan
authors: School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.
authors: Karen
authors: K
authors: Francis
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.
authors: Akiko
authors: A
authors: Enju
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|ACRF South Australian Cancer Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, SA, 5000, Australia.|School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, SA, 5000, Australia.
authors: John
authors: J
authors: Toubia
authors: Australian Centre for Plant Functional Genomics, School of BioSciences, The University of Melbourne, Parkville, VIC, 3010, Australia.|Metabolomics Australia, School of BioSciences, The University of Melbourne, Parkville, VIC, 3010, Australia.
authors: Ute
authors: U
authors: Roessner
authors: Metabolomics Australia, School of BioSciences, The University of Melbourne, Parkville, VIC, 3010, Australia.|ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, The University of Melbourne, Parkville, VIC, 3010, Australia.
authors: Antony
authors: A
authors: Bacic
authors: DuPont Pioneer, Wilmington, DE, 19803, USA.
authors: Antoni
authors: A
authors: Rafalski
authors: DuPont Pioneer, Johnston, IA, 50131, USA.|International Maize and Wheat Improvement Center (CIMMYT), Carretera México Veracruz, Km. 45, El Batán, Texcoco, Estado De México, 56237, USA.
authors: Kanwarpal S
authors: KS
authors: Dhugga
authors: Center for Desert Agriculture, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia.
authors: Mark
authors: M
authors: Tester
authors: Australian Centre for Plant Functional Genomics, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia. trevor.garnett@adelaide.edu.au.|School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia. trevor.garnett@adelaide.edu.au.|The Plant Accelerator, Australian Plant Phenomics Facility, The University of Adelaide, PMB 1, Glen Osmond, 5064, Australia. trevor.garnett@adelaide.edu.au.
authors: Trevor
authors: T
authors: Garnett
authors: School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Adelaide, SA, 5064, Australia.|Centre For Carbon Water and Food, The Faculty of Agriculture and Environment, The University of Sydney, Camden, NSW, 2570, Australia.
authors: Brent N
authors: BN
authors: Kaiser
mesh_terms: D018506:Gene Expression Regulation, Plant; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D040641:Quantitative Trait Loci / Q000235:genetics; D003313:Zea mays / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*
chemical_list: D009584:Nitrogen
keywords: Amino acids; Enzyme activity; NUE; Nitrogen metabolism; Nitrogen use efficiency; Transcript abundance