Nitrogen (N) is a major input determining productivity, with considerable financial and environmental costs. N is required for canopy formation for efficient carbon capture, thus determining yield.

N use efficiency (NUE) (yield/available N) is the product of N uptake efficiency (N taken up/N available) and N utilization efficiency (yield/N taken up). Component traits will be de-convoluted and component genes identified, exploiting variation in alleles and expression profiles in modern wheat cultivars. Roles of nitrate transporters in the roots in controlling uptake processes will be determined: cellular nitrate pools will be measured and compared in soil grown roots of selected cultivars; nitrate influx will be measured on roots growing in soil; the wasteful loss of nitrate from root cells through the efflux pathways will be assessed; key nitrate transporters involved in sensing N availability and uptake will be characterised.

Traits associated with NUtE (N and carbon assimilation and partitioning) will be de-convoluted, mapped and data made available for modelling studies. N is utilised for canopy production/photosynthesis which subsequently determines yield and this same N is utilised for grain formation, obviating the need for further uptake. Timing of senescence is critical to extend the photosynthetically active period and to maximise N transfer to the grain. We will investigate variation in associated parameters (canopy architecture, photosynthetic capacity, N storage and remobilisation) screening germplasm, functional staygreen mutants and transgenic lines. Key genes, both those involved in the pathways themselves or in the control of the pathways (transcription factors, signalling pathways) which underpin NUE traits will be identified using mapping approaches and transcriptomics.

An important resource is the Defra Wheat Genetic Improvement Network field trial.

The key output will be the dissection of the complex trait of nitrogen use efficiency into component processes and the determination of existing variation in these processes and overall agronomic performance across a range of elite germplasm and mapping populations at a range of nitrogen inputs. In addition new QTLs for N use efficiency will be identified and this will be the first step in the forward genetics pipeline for fine mapping and new gene discovery in bread wheat. Additional research arising from this project will include wider germplasm screening (landraces, wild relatives and additional mapping populations) and validation in transgenic lines of key gene function, particularly for overall pathway/trait control via signalling pathways and transcription factors, with the potential for delivery of improved transgenic lines/markers for breeding. Genes controlling canopy longevity/photosynthetic capacity, controls of nitrogen remobilisation will be identified and placed into pipelines for validation and delivery to pre-breeding. Transgenic lines with manipulated traits will be generated and available for further study. Goals will be varieties with optimised yields at current or reduced nitrogen input levels, for wheats with specified end uses (starch/protein optimisation).

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