Nitrogen Use Efficiency
Nitrogen (N) is an essential macronutrient and a major structural and physiological component of basically all processes related to plant development, growth and reproduction. For sustainable agriculture and food production, N is indispensable and it therefore has to be re-supplied to agricultural soils to prevent nutrient depletion and soil degradation.
Globally, more than 100 million tonnes of N fertiliser are applied to croplands each year – however, only about 40% of the fertilizer is effectively used by the crop plant and converted into harvested crop yield.
Apart from being economically wasteful, this is costly to the environment. Nitrogen pollution of waterways is a global problem and emission of nitrous oxide (a gas with more than 300 times the global warming power than CO2) is estimated to account for more than 7% of the human-influenced greenhouse effect. Therefore, there are many good reasons to study nitrogen in plants and to apply this knowledge to work towards improving nitrogen use efficiency (NUE) in crops.
From left: Julie Hayes, Pia Mueller, Alberto Casartelli, Nick Hansen, Jacinda Rethus, Jessey George, Akiko Enju, Darren Plett, Sigrid Heuer,
Our multi-national, multi-disciplinary NUE team has currently ongoing projects
Improvement of internal NUE and maintenance of high grain nitrogen
This project is part of the ARC Research Hub “Genetic Diversity and Molecular Breeding for Wheat in a Hot and Dry Climate”. Within the NUE component of this five-year project, we are investigating natural genetic diversity for NUE in wheat. Recent field trials confirmed the existence of genetic diversity for NUE and N-responsiveness in selected modern Australian spring wheat cultivars. Population studies revealed that several yield QTL are related to N-responsiveness and those are potential markers to improved NUE in wheat by molecular breeding.
Grain protein concentration and grain size are also traits of interest because it is a challenge for breeders and grain growers to achieve both, high grain yield and high grain protein concentration (GPC). Within this project we will address this problem using diverse, contrasting wheat genotypes, identify the genes that control GPC and understand the physiological bottlenecks of N remobilization and grain N loading.
Control points in nitrogen uptake: Enhancing the response of cereals to N supply and demand
This project will identify control points in the nitrogen- uptake pathways responsible for limiting plants’ nitrogen uptake. We have engineered the N-uptake pathway by manipulating these points via genetic transformation of candidate genes into wheat and maize. Currently we are phenotyping NUE and N-uptake efficiency of these transgenic plants using a high-throughput phenotyping screen which mimics field conditions. A crucial outcome of this project will be the development of cereals that use nitrogen fertiliser more efficiently.
Small molecules with large effect: The dual role of nitrogen-containing metabolites in stress tolerance and nutrient recycling
Within this project we conduct targeted and untargeted metabolite profiling using diverse wheat genotypes exposed to different water and nitrogen conditions. Ultimately, this project aims at identifying genes and pathways, and related molecular markers that can be used for breeding of N-use efficient plants in stress environments, particularly drought.
Genetic diversity for N uptake and N-root responses in wheat
The diverse activities covered under this project title mainly aim at developing a better understanding of N uptake and N assimilation in wheat and include the characterization and identification of allelic variation of relevant genes within diverse wheat genotypes. Another area of interest is to characterize root responses to N starvation and in relation to drought, and to study changes of the root architecture and root internal structure. In this context, root image analysis software was developed to enable semi-high throughput root analyses.
Enhancing NUE using the Alanine Aminotransferase technology
We have been evaluating the alanine aminotransferase (AlaAT) NUE technology in wheat, barley and rice. Selected transgenic wheat and barley plants were tested and showed some yield advantage under normal growth conditions both in the field and glasshouse. In collaboration with Arcadia Biosciences, the rice transgenic events with this technology have been characterised at the molecular and physiological level. Transgenic rice plants produced larger biomass and increased seed number under low N conditions. Metabolomics and transcriptomics analyses are underway to understand the mechanism of the technology.
Our project collaborators:
Brent Kaiser (University of Sydney, Australia)
We are grateful to ARC and GRDC and our commercial partners for supporting our NUE research.
Recent selected publications:
Cai J, Zeng Z, Connor JN, Huang CY, Melino V, Kumar P, SJ Miklavcic (2015). RootGraph: a graphic optimization tool for automated image analysis of plant roots. J Exp Bot doi:10.1093/jxb/erv359
Chiasson DM, Loughlin PC, Mazurkiewicz D, Mohammadidehcheshmeh M, Fedorova EE, Okamoto M, McLean E, Glass ADM, Smith SE, Bisseling T, Tyerman SD, Day DA, and Kaiser BN (2014). Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH4+ transport. Proc. Natl. Acad. Sci. U. S. A. 111: 4814-4819.
Chopin J, Laga H, Huang CY, Heuer S, Miklavcic SJ (2015). RootAnalyzer: a cross-section image analysis tool for automated characterization of root cells and tissues. PLOS ONE. Accepted.
Garnett T, Conn V, Plett D, Conn S, Zanghellini J, Mackenzie N, Enju A, Francis K, Holtham L, Roessner U, Boughton B, Shirley N, Rafalski A, Dhugga K, Tester M, Kaiser BN. 2013. The response of the maize nitrate transport system to nitrogen demand and supply across the lifecycle. New Phytologist 198(1): 82-94.
Garnett T, Plett D, Heuer S, Okamoto M (2015). Genetic approaches to enhancing nitrogen-use efficiency (NUE) in cereals: challenges and future directions. Functional Plant Biology (in press).
Han M, Okamoto M, Beatty PH, Rothstein SJ, and Good AG (2015). The Genetics of Nitrogen Use Efficiency in Crop Plants. Annual Review of Genetics 49.
Melino VJ, Fiene G, Enju A, Cai J, Buchner P, Heuer S (2015). Genetic diversity for root plasticity and nitrogen uptake in wheat seedlings. Functional Plant Biology doi.org/10.1071/FP15041.
Plett D, Toubia J, Garnett T, Tester M, Kaiser BN, Baumann U (2010). Dichotomy in the NRT families of dicots and grass species. PLoS ONE 5(12): e15289.
Plett D, Baumann U, Schreiber AW, Holtham L, Kalashyan E, Toubia J, Nau J, Beatty M, Rafalski A, Dhugga KS, Tester M, Garnett T, Kaiser BN (2015). Maize maintains growth in response to decreased nitrate supply through a highly dynamic and developmental stage-specific transcriptional response. Plant Biotechnology Journal (in press).