TaAGL6-B1 identified as a candidate gene for the dominant awn-inhibitor locus B2 in wheat

Identification of TaAGL6-B1 as the candidate gene underlying the B locus reveals its role as a key regulator of awn suppression in wheat2. A nonsynonymous substitution causes ectopic expression of TaAGL6-B1 in lemmas, repressing TaDL and inhibiting awn elongation. These findings elucidate the genetic network controlling awn development and provide molecular insight for wheat breeding. Awns are photosynthetically active structures that extend from the lemma and enhance grain filling and drought tolerance in wheat (Triticum aestivum L.), where their development is regulated by three major loci: B1 (Tipped1), B2 (Tipped2), and Hd (Hooded). The aim of this study was to identify the gene encoding the B2 locus, whose molecular identity remains elusive despite its central role in awn suppression. Fine mapping and association analyses identified TaAGL6-B1, an AGAMOUS-LIKE 6 transcription factor gene homologous to rice OsMADS6, as the most likely candidate gene. A non-synonymous substitution in the conserved K-box domain was strongly associated with awn phenotype. Cultivars carrying this amino acid substitution exhibit ectopic expression of TaAGL6-B1 in the lemma, the tissue from which they originate. Furthermore, we identified a cultivar that harbours an amino acid change and exhibits ectopic expression of TaAGL6-B1, yet retains long awns. Genomic sequencing of the TaAGL6-B1 allele in this cultivar revealed an 869-bp insertion in exon 8, resulting in a frameshift mutation that leads to loss of gene function. Additionally, the expression level of TaDL, a wheat orthologue of DROOPING LEAF (DL), which promotes awn elongation in rice, was elevated in long-awned cultivars and closely correlated with awn phenotype. Given that OsMADS6 represses DL in rice, ectopic expression of TaAGL6-B1 in lemmas could inhibit awn elongation by repressing TaDL. These findings strongly support TaAGL6-B1 as a B2 candidate gene and provide novel insights into the genetic network regulating awn development in wheat.