Barley FASCIATED EAR genes determine inflorescence meristem size and yield traits

In flowering plants, the inflorescence meristem (IM) provides founder cells to form successive floral meristems, which are precursors of fruits and seeds. The activity and developmental progression of IM are thus critical for yield production in seed crops. In some cereals, such as rice (Oryza sativa) and maize (Zea mays), the size of undifferentiated IM, which is located at the inflorescence apex, is positively associated with yield traits such as spikelet number. However, the relationship between IM size and yield-related spike traits remains unknown in the Triticeae tribe. Here we report that IM size has a negative correlation with yield traits in barley (Hordeum vulgare). Three FASCIATED EAR (FEA) orthologs, HvFEA2, HvFEA3, and HvFEA4, regulate IM size and spike morphogenesis and ultimately affect yield traits. Three HvFEAs genes are highly expressed in developing spikes, and all three loss-of-function mutants exhibit enlarged IM size, shortened spikes, and reduced spikelet number, which may lead to reduced grain yield. Natural variations identified in HvFEAs indicate selection events during barley domestication. We further reveal that HvFEA4, as a transcription factor, potentially targets multiple pathways during reproductive development, including transcriptional control, phytohormone signaling, and redox status. The roles of barley FEA genes in limiting IM size and promoting spikelet formation suggest the potential of increasing yield by manipulating IM activity.