Identification of Mutants with Altered Seminal Root Numbers in Hexaploid Wheat

Root development in wheat, the most widely grown crop in the world suppling 20% of global calorifie intake, remains a black-box process. Despite progress in understanding the molecular control of root development in model species, only a single gene regulating root architecture has been cloned in wheat. This is partly due to the large size of the wheat genome (~17 GB), its high repeat content (>80%) and the genetic redundancy of this polyploid species. To improve our understanding of the genetic control of root development in wheat, we conducted a forward genetic screen for seminal root number using an exome-sequenced hexaploid wheat TILLING population. The screen identified seven mutants with homozygous and stable altered seminal root number (hereafter referred to as arn1- arn7) phenotypes. arn1 displays a higher number of seminal root compared to wild-type plants while arn2- arn7 show lower number of seminal roots. We further characterised the genetic architecture of arn1 and arn2 phenotypes and show that arn1 segregates as a recessive multigenic mutation while arn2 segregate as a dominant monogenic mutation. This suggests that multiple pathways determine the establishment of seminal root number in wheat. Our work highlights the potential to use the sequenced wheat TILLING population as a forward genetic resource for uncovering novel variation in seminal root architecture that can be useful for understanding root development in wheat.