Genetic Basis of Nitrogen Use Efficiency and Yield Stability Across N Conditions in Rapeseed: Combining Quantitative Genetic and Functional Genomic Approaches

Improving nitrogen use efficiency is of major interest as low nitrogen-inputs cultural practices have to be developed to face economic and environmental issues. Rapeseed is known as a low “nitrogen use efficiency” crop, resulting mainly from non-efficient N-remobilization processes. In this study we aimed at characterizing the genetic and physiological determinant of Nitrogen Use Efficiency for rapeseed both considering the field scale with the impact of a nitrogen limitation on seed yield, and the physiological scale by targeting N-remobilization processes. We carried out QTL detection for NUE-traits both by linkage analyses and genome-wide association studies for the seed yield on a field network representing French growing conditions, under high and low conditions. The N-specific QTL were confronted to functional candidates resulting from an RNAseq analysis performed on rapeseed cultivar “aviso” grown in a greenhouse, under contrasted N regimes, where different leaves categories where considered according to their senescence (source) vs mature (sink) status. N-responsive and/or senescence-specific genes sets were selected on the basis of their expression profiles. All QTL and candidate genes were projected on the Darmor-bzh sequence. QTL were more modulated by environmental conditions than by N conditions in the field, however, 9 N-specific QTL were identified, whereas 51 QTL were detected as non-modulated, neither by environments nor by Nitrogen. Within each group of differentially expressed genes, co-localization of genes and QTL has been investigated. The added value provided by gene expression data to unravel the function underlying the QTL will be presented.