* ballvora@uni-bonn.de

Breeding crop varieties with improved nitrogen use efficiency (NUE) is critically important for minimizing nutrient losses as well as reducing the costs related to excess fertilizer application. Achieving efficient N-uptake and transport relies on a beneficial root system architecture, but the genetic and molecular mechanisms underlying NUE are not yet well-explored in wheat.

We performed genome-wide association analyses using a genetically diverse panel of winter wheat to analyze root trait phenotypes under extreme N-deprivation levels in the field and under high N condition. We identified several marker-trait associations for root architecture traits with underlying candidate genes involved in N transport and metabolism. One of these genes, NPF2.12, shares homology with Arabidopsis nitrate transceptors. The expression of a rare regulatory-element-based natural allele of NPF2.12 was associated with significantly enhanced root growth and root-to-shoot nitrogen translocation at low N availability.

In agreement with this, under limited N conditions the NPF2.12 allele shows reduced expression and lines carrying this allele display increased NITRATE REDUCTASE 1 (NIA1) expression that possibly leads – through increased NR-mediated NO biosynthesis - to root growth and root-to-shoot N translocation. We intend to increase the variability at the NPF2.12 locus by searching for natural allelic variants and by developing various alleles via genome-editing approaches that will both permit to analyse the regulatory mechanisms and select more efficient allelic variants.

Similar findings were observed in barley. Our study provides a better understanding of the molecular mechanisms underlying the process of nitrate sensing and modulation through root developmental adjustments of nitrogen uptake and translocation in cereals, and suggests genes which can be exploited to improve root growth and NUE under low N availability.