Whole genome sequencing uncovers the structural and transcriptomic landscape of hexaploid wheat/Am. muticum introgression lines

Wheat is a globally vital crop, but its limited genetic variation creates a challenge for breeders aiming to maintain or accelerate agricultural improvements over time. Introducing novel genes and alleles from wheat's wild relatives into the wheat breeding pool via introgression lines is an important component of overcoming this low variation but is limited by poor genomic resolution and limited understanding of the genomic impact of introgression breeding. By sequencing 17 hexaploid wheat/Ambylopyrum muticum introgression lines and the parent lines, we have precisely pinpointed the borders of introgressed segments. We report a genome assembly and annotation of Am. muticum that has facilitated the identification of Am. muticum resistance genes commonly introgressed in lines resistant to stripe rust. Our analysis has identified an abundance of structural disruption and homoeologous pairing across the introgression lines, likely caused by the suppressed Ph1 locus. mRNAseq analysis of six of these introgression lines revealed that introgressed genes tend to be downregulated, shifting the expression balance of triads towards suppression of the introgressed region, with no discernible compensation in the expression of the homoeologous copies. This analysis explores the genomic impact of introgression breeding and provides an affordable way for breeders to better characterise introgression lines and more effectively deploy wild relative variation.