The awn in grasses is a needle-like structure at the tip of the spikelet. In contrast to rice, where the awn was eliminated through the process of domestication, the presence of the awn in barley is of significant agronomic importance due to its role in enhancing seed yield via photosynthesis. In barley, various awn related mutants have been reported, but their causal genes are largely unidentified. Overall mechanism of awn development in barley is still elusive, compared to other cereal crops.
To gain a better understanding of the mechanism behind barley awn formation, we analyzed the short and crooked awn (sca) mutant. Through mapping, we identified that SCA encodes a protein associated with histone modification. Comparative RNA-seq analysis between sca and the wild type not only revealed alterations in the expression of known awn-related genes but also showed ectopic expression of specific floral homeotic genes. Additionally, a downregulation of genes involved in cell division and elongation was observed in the sca mutant. Furthermore, chromatin immunoprecipitation revealed reduced levels of H3K27me3, a repressive histone mark, in loci of homeotic genes governing floral development and plant architecture, suggesting a consequent de-repression of these genes in the sca mutant. Transgenic barley plants overexpressing the floral homeotic gene which is presumed main downstream target of SCA exhibited a reduction of awn length up to 40%. Based on these results, we propose a model that SCA regulates barley awn development by modulating histone modifications of floral homeotic genes in proper timing.