Three dominant awnless genes in common wheat: Fine mapping, interaction and contribution to diversity in awn shape and length

Abstract

The awn is a long needle-like structure formed at the tip of the lemma in the florets of some grass species. It plays a role in seed dispersal and protection against animals, and can contribute to the photosynthetic activity of spikes. Three main dominant inhibitors of awn development (Hd, B1 and B2) are known in hexaploid wheat, but the causal genes have not been cloned yet and a genetic association with awn length diversity has been found only for the B1 allele. To analyze the prevalence of these three awning inhibitors, we attempted to predict the genotypes of 189 hexaploid wheat varieties collected worldwide using markers tightly linked to these loci. Using recombinant inbred lines derived from two common wheat cultivars, Chinese Spring and Mironovskaya 808, both with short awns, and a high-density linkage map, we performed quantitative trait locus analysis to identify tightly linked markers. Because this linkage map was constructed with abundant array-based markers, we converted the linked markers to PCR-based markers and determined the genotypes of 189 hexaploids. A significant genotype-phenotype correlation was observed at the Hd and B1 regions. We also found that interaction among these three awning inhibitors is involved in development of a membranous outgrowth at the base of awn resembling the Hooded mutants of barley. For the hooded awn phenotype, presence of the Hd dominant allele was essential but not sufficient, so B2 and other factors appear to act epistatically to produce the ectopic tissue. On the other hand, the dominant B1 allele acted as a suppressor of the hooded phenotype. These three awning inhibitors largely contribute to the genetic variation in awn length and shape of common wheat.

Domestication and crop evolution of wheat and barley: Genes, genomics, and future directions

“…In wheat, three awnless genes (Hd, B1 and B2) have been mapped, but not cloned (Sourdille et al 2008;Yoshioka et al 2017). In barley, one of the bestcharacterized short awn genes is Lks2, which encodes a transcription factor (TF) from the SHORT INTERNODE (SHI) family (Yuo et al 2012).…”

Sequence‐based mapping identifies a candidate transcription repressor underlying awn suppression at the B1 locus in wheat

“…The B2 allele reduces awn length most dramatically towards the top and bottom of the wheat spike, while the Hd allele reduces awn length consistently and can produce curved, 'hooked' awns (Watkins & Ellerton, 1940). Combination of these genes produces a nearly awnless or completely awnless phenotype (Yoshioka et al, 2017). None of the genes controlling awn length in wheat have been cloned, but mapping studies place Hd and B2 on the short arm of chromosome 4A and the long arm of chromosome 6B, respectively (Sourdille et al, 2002;Yoshioka et al, 2017).…”

“…Combination of these genes produces a nearly awnless or completely awnless phenotype (Yoshioka et al, 2017). None of the genes controlling awn length in wheat have been cloned, but mapping studies place Hd and B2 on the short arm of chromosome 4A and the long arm of chromosome 6B, respectively (Sourdille et al, 2002;Yoshioka et al, 2017). The B1 locus has a long history as a physical marker, and is located distal to the major genes controlling vernalization requirement (VRN-A1) and the spelt head type (Q) on 5AL (Kato et al, 1998).…”

“…In rice, awn suppression is an important domestication trait and is derived from mutations in genes involved in awn development: a helix-loop-helix protein Awn-1 (An-1), an auxin response factor OsETT2, a YABBY transcription factor DROOPING LEAF (DL), LONG AND BARBED AWN (LABA1) involved in cytokinin biosynthesis, and an EPIDERMAL PATTERNING FACTOR-LIKE 1 (EPFL1) gene REGULATOR OF AWN ELONGATION 2 (RAE2) or GRAIN NUMBER, GRAIN LENGTH AND AWN DEVELOPMENT1 (GAD1) (Luo et al, 2013;Toriba & Hirano, 2013;Hua et al, 2015;Bessho-Uehara et al, 2016;Jin et al, 2016). However, awn suppression in wheat does not appear to be related to these genes (Yoshioka et al, 2017).…”

Characterization of novel mutants of hexaploid wheat (Triticum aestivum L.) with various depths of purple grain color and antioxidant capacity

“…In hexaploid wheat, three dominant inhibitors regulate awn development: Hooded, Tipped1 and Tipped2; these genes reside on chromosomes 4AS, 4AL and 6BL respectively. 29 A recent study identified three quantitative trait loci (QTL) associated with awns on chromosomes 2DS, 5AL and 6BL: QALT.ndsu.2D, QALT.ndsu.5A and QALM.ndsu.6B.1 respectively. 30 It is possible that gamma irradiation induced mutations in one or more genes that regulate awn production, thus changing the awn phenotype of L47 and L167.…”