Fine mapping and characterization of the awn inhibitor B1 locus in common wheat (Triticum aestivum L.)

Awns play an important role in seed dispersal and photosynthesis of spikes. Three major awn inhibitors (Hd, B1, and B2) are reported in wheat. However, the molecular mechanism underlying awnlessness remained unknown until recently. In this study, we identified two F₈ recombinant inbred lines (RILs) that were segregating for awn length. In order to identify the causal gene for awn length in the heterozygous inbred families (HIFs), SNPs were called from RNA sequencing (RNA-Seq) data for HIF-derived progenies with long and short awns. SNPs between long and short awn plants were evenly distributed on chromosomes (chr) other than chromosome 5A. SNPs on chr 5A were clustered in a region distal 688 Mb on the long arm, where inhibitor B1 was located. This suggested that B1 was the causal segregating locus. We precisely mapped B1 to ~1 Mb region using two HIF-derived families. Considering that the lines segregated for long, intermediate and short awn phenotypes we speculated that B1 should have a dosage effect on awn length. Two differentially expressed genes (DEGs) located in the candidate region were regarded as candidate genes for B1, because the molecular expression pattern was consistent with the phenotype. HIFs with long and short awns showed no difference on grain yield and other agronomic traits.