Root systems architecture (RSA) is crucial for crop performance, particularly under non-optimal water and nutrients supply conditions. Root ideotypes that facilitate water or nutrient absorption and their use efficiency have been proposed to enhance crop stress resilience. However, knowledge of genes, developmental programs and regulatory circuits governing these ideotypes in crops is largely missing or not ready to be exploited in breeding.

Seven QTLs controlling root growth angle (RGA) were identified in durum wheat (Triticum turgidum ssp. durum) combining linkage mapping and association mapping (Maccaferri et al., 2016). RGA determines the direction of root growth and narrow RGA generally results in deeper root systems that could better capture water and nitrogen in deep soil layers. This study reports new results on the genetic control of RGA based on a wider genome wide association study and integrated with RNA-Seq and Gene Coexpression Network (GCN) analyses. An improved GWAS pipeline applied to the Global Durum Panel (GDP), a world-wide tetraploid collection composed of 755 accessions, confirmed the previously identified major RGA-QTLs on chromosomes 2A, 6A and 7A and also allowed the identification of two additional RGA-QTLs on chromosomes 5B and 7A, that are under further investigation. Transcriptome analysis was performed on root tips (including root cap and meristematic region), elongation and transition/maturation zones. Roots were collected from four shallow RGA and four narrow RGA genotypes, carrying contrasting haplotypes at the three major QTLs confirmed by an improved GWAS pipeline applied to a collection of 755 accessions of tetraploid wheat. Differentially expressed genes (DEGs) showing RGA-related expression levels and mapping in the RGA-QTL intervals resulted involved in auxin signalling, melatonin biosynthesis, hormone signalling and cross-talk and cell wall biosynthesis. These candidate genes were predicted as hub genes in modules associated to auxin-mediated root development. Complete analysis of co-expressed genes and regulatory networks associated to wide or narrow RGA in durum wheat are underway, with preliminary results pointing to a main role for abscisic acid signalling components.