VULGARE ROW-TYPE SIX 5 binds to the promoter of tillering and floral homeotic genes to regulate their expression.

Variation in shoot architecture, or tillering, is an important adaptive trait targeted during the domestication of crops. A well-known regulatory factor in shoot architecture is TEOSINTE BRANCHED 1 (TB1). TB1 and its orthologs have a conserved function in integrating environmental signals to regulate axillary branching or tillering in cereals. The barley (Hordeum vulgare) ortholog of TB1, VULGARE ROW-TYPE SIX 5 (VRS5), regulates tillering and is involved in regulating row-type by inhibiting lateral spikelet development. These discoveries predominantly come from genetic studies; however, how VRS5 regulates these processes on a molecular level remains largely unknown. By combining transcriptome analysis between the vrs5 mutant and the wild type at different developmental stages and DAP-sequencing to locate the genome-wide DNA binding sites of VRS5, we identified bona fide targets of VRS5. We found that VRS5 targets abscisic acid-related genes, potentially to inhibit tillering in a conserved way. Later in inflorescence development, VRS5 also targets row-type gene VRS1 and several known floral development genes, such as MIKCc-type MADS-box genes. This study identifies several genes for mutational analysis, representing a selection of bona fide targets that will contribute to a deeper understanding of the VRS5 network and its role in shaping barley development.