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Awns are stiff, hair-like structures that grow from the spikelets of wheat (Triticum aestivumL.) and other grasses. In wild wheat relatives, awns play a role in seed dispersal. Awn suppression in domesticated wheat, where awns are shortened or even eliminated entirely, is variably adaptive with both awned and awnless types under widespread cultivation. Although theB1locus on the long arm of chromosome 5A is a major determinant of awn suppression, no underlying gene or mechanism of action has been identified. Using association mapping, we identified a SNP marker located on the distal end of 5AL (5A28417) predictive of awn status in a panel of 640 U.S. winter wheat breeding lines, indicating thatB1was the determinant of awn suppression in this germplasm. Analysis of historical data available for the panel determined5A28417was also significantly associated with grain test weight. Evaluation of spike morphology and kernel traits was undertaken in a 341 RIL population developed from a cross between awned soft winter wheat cultivar LA95135 and awnless cultivar SS-MPV57. Awn suppression in the population co-segregated with 5A28417 and was co-located with QTL for number of spikelets per spike, kernel weight and kernel length. Fine-mapping locatedB1to a region containing only two predicted genes, including a C2H2 zinc finger transcription factor 219 bp from 5A28417 that we namedAWNS-A1. Deletions encompassing both genes were present in awned mutants of the awnless cultivar Brundage. Polymorphisms in theAWNS-A1coding region were not observed in diverse wheat germplasm. However, sequencing of wheat lines representing different marker haplotypes in the surrounding region identified a deletion 3 kb downstream ofAWNS-A1.A marker for this deletion was highly predictive of awn suppression in a collection of diverse wheat accessions, and indicates thatAWNS-A1is likely the major determinant of awn suppression in global wheat germplasm.AWNS-A1is more highly expressed in developing spikes of awnless individuals, suggesting a mechanism for awn suppression. |
