SHORT AND CROOKED AWN, Encoding an Epigenetic Regulator EMF1, Promotes Barley Awn Development.

Abstract

The awn is a bristle-like extension from the lemma of grass spikelets. In barley, the predominant cultivars possess long awns that contribute to grain yield and quality through photosynthesis. Barley is a useful cereal crop to investigate the mechanism of awn development as various awn morphological mutants are available. Here, we identified the gene causative of the short and crooked awn (sca) mutant, which exhibits a short and curved awn phenotype. Intercrossing experiments revealed that the sca mutant induced in the Japanese cultivar (cv.) 'Akashinriki' is allelic to independently isolated moderately short-awn mutant breviaristatum-a (ari-a). Map-based cloning and sequencing revealed that SCA encodes the Polycomb group-associated protein EMBRYONIC FLOWER 1 (EMF1). We found that SCA affects awn development through the promotion of cell proliferation, elongation, and cell wall synthesis. RNA sequencing of cv. Bowman (BW) backcross-derived near-isogenic lines of sca and ari-a6 alleles showed that SCA is directly or indirectly involved in promoting the expression of genes related to awn development. Additionally, SCA represses various transcription factors essential for floral organ development and plant architecture, such as MADS-box and KNOX1 genes. Notably, the repression of the C-class MADS-box gene HvMADS58 by SCA in awns is associated with the accumulation of the repressive histone modification H3K27me3. These findings highlight the potential role of SCA-mediated gene regulation, including histone modification, as a novel pathway in barley awn development.