Induced variation in BRASSINOSTEROID INSENSITIVE 1 (BRI1) confers a compact wheat architecture

The brassinosteroid (BR) plant hormones regulate numerous developmental processes, including those determining stem height, leaf angle, and grain size that have agronomic relevance in cereals. Indeed, barley (Hordeum vulgare) varieties containing uzu alleles that impair BR perception through mutations in the BR receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) exhibit a semi-dwarf growth habit and more upright leaves suitable for high-density planting. We used forward and reverse genetic approaches to develop novel BRI1 alleles in wheat (Triticum aestivum L.) and investigated their potential for crop improvement. The combination of ethyl methanesulfonate-induced mutations introducing premature stop codons in all three homoeologous TaBRI1 genes resulted in severe dwarfism, malformed leaves and sterility as observed in bri1 mutants in other species. Double mutants had reduced flag leaf angles (FLAs) conferring a more upright canopy but exhibited no differences in height or grain weight. In a forward genetics screen using a double mutant, we identified two BR-insensitive lines with reduced height and FLA that contained amino acid substitutions in conserved regions of BRI-A1. The less severe mutant had a 56% reduction in FLA and was 35% shorter than the wild-type although seed set, seed area and grain weights were also reduced. The most severe mutants contained elevated levels of bioactive BRs and increased expression of BR-biosynthesis genes consistent with reduced feedback suppression of biosynthesis. Our study gives a better understanding of BRI1 function in wheat and provides mutants that could potentially be explored for improving grain yields when sown at high density. RNA-seq was conducted on tabri1-a.1bd, tabri1-a.2bd, tabri1-a.3bd, tabri1-bd mutants and wild-types TaBRI1-NS and Cadenza. The entire above-ground tissue for all genotypes was harvested at 2nd leaf seedling stage and multiple seedlings/genotype were pooled together to make one biological replicate. This experiment was conducted using 4 biological replicates for all genotypes except for 3 reps for tabri1-a.1bd mutant due to tissue limitations. The trimmed paired-end reads were mapped to wheat IWGSC RefSeq v2.1 genome assembly. The raw mapped reads were counted and converted to TPM's (transcripts per million). The raw data (.fastq) and TPM's are included in this project.