The cultivated barley inflorescence is divided into two major spike forms, ‘two-rowed’ and ‘six-rowed’ spikes based on the fertility of their lateral spikelets. The six-rowed phenotype has been selected during domestication. The Six-rowed spike 1 (Vrs1) gene were identified among natural row-type variants of the cultivated barley gene pool. Vrs1 encodes an HD-Zip I transcription factor and is predominantly expressed in the lateral florets, especially in the pistil, lemma, and palea, but also in the rachilla (Komatsuda et al., 2007; Sakuma et al., 2013). Loss-of-function mutations of Vrs1 contribute to higher grain number per spike through a complete conversion from sterile to fertile lateral florets.