Developmental Genetics of Reproductive Architecture in Barley

The selection of beneficial architectural variation in cereals, especially of the grain-bearing inflorescence, remains key to increasing grain yield. The barley inflorescence is an unbranched spike with the central axis or rachis flanked by alternate triple spikelet clusters, each arranged into a central spikelet and two laterals. Depending on whether the central spikelets alone or the central and both lateral spikelets are fertile, the spike forms two or six rows of grain, respectively. In two-rowed barley, multiple Six-rowed spike or VRS loci act to repress lateral fertility. Of the four VRS genes cloned to date - VRS1, VRS2, VRS4 and VRS5 - all encode transcription factors. Here, we add to the known VRS genes and identify VRS3 as an epigenetic modifier. Exploiting a near-isogenic mutant panel, we show that defective vrs3 in combination with other vrs alleles lead to novel, improved routes to fully six-rowed grain set. Our analyses of higher-order mutants reveal that VRS3, along with VRS4 or VRS5, are also required for spikelet determinacy to establish barley’s species-specific unbranched spike and triple spikelet form. Lastly, we expand the role of VRS3, VRS4 and VRS5 outside of the spike, revealing a shared role in regulating whole plant branching. Our data support a model where VRS genes function together to regulate reproductive architecture of barley and where tweaking the combined contribution of specific VRS genes can reveal novel pathways to improving yield.