Twisted Sister1 : an agravitropic mutant of bread wheat ( Triticum aestivum ) with altered root and shoot architectures

We identified a mutant of hexaploid wheat ( Triticum aestivum ) with impaired responses to gravity. The mutant named Twisted Sister1 ( TS1 ) had agravitropic roots that were often twisted along with altered shoot phenotypes. Roots of TS1 were insensitive of externally applied auxin with the genetics and physiology suggestive of a mutated AUX/IAA transcription factor gene. Hexaploid wheat possesses over eighty AUX/IAA genes and sequence information did not identify an obvious candidate. Bulked segregant analysis of an F ₂ population mapped the mutation to chromosome 5A and subsequent mapping located the mutation to a 41 Mbp region. RNA-seq identified the TraesCS5A03G0149800 gene encoding a TaAUX/IAA protein to be mutated in the highly conserved domain II motif. We confirmed TraesCS5A03G0149800 as underlying the mutant phenotype by generating transgenic Arabidopsis thaliana . Analysis of RNA-seq data suggested broad similarities between Arabidopsis and wheat for the role of AUX/IAA genes in gravity responses. Here we show that the sequenced wheat genome along with previous knowledge largely from the model species Arabidopsis, gene mapping, RNA-seq and expression in Arabidopsis have enabled cloning of a key wheat gene defining plant architecture.