Rapid development of naked malting barley germplasm through targeted mutagenesis

Covered barley (Hordeum vulgare) has historically been preferred for malting, as the husk in this plant protects the embryo during harvest and acts as a filter during brewing. Naked barley, which is typically used as food, has the potential to be used in brewing due to recent technical advances, but the grains contain higher levels of β-glucan and polyphenols, which are undesirable in brewing. Introducing the naked trait into brewing cultivars through crossing is time-consuming due to the need to eliminate these undesirable traits. In this study, we rapidly developed naked barley that is potentially suitable for malting by introducing targeted mutations into Nudum (NUD) using CRISPR/Cas9-mediated targeted mutagenesis. The doubled haploid line ‘DH120366’, which was used as the parental line, was derived from a cross between two covered malting barley cultivars. We generated CRISPR/Cas9-mediated targeted mutagenized barley harboring mutations in NUD via Agrobacterium tumefaciens-mediated transformation and confirmed the presence of mosaic mutations in one individual from among 16 T0 transformants. We sowed T1 grains exhibiting the naked trait and sequenced the NUD gene in these T1 seedlings, identifying two types of mutations. Shotgun high-throughput whole-genome sequencing confirmed the absence of the transgene in at least one nud mutant line following k-mer-based analysis. Cultivation in a closed growth chamber revealed no significant differences in agronomic traits between the nud mutants and the wild type. This study demonstrates the feasibility of rapidly developing naked barley with potential use for malting and brewing by targeting only NUD via targeted mutagenesis.