<i>GRASSY TILLERS1</i> (<i>GT1</i>) and <i>SIX-ROWED SPIKE1</i> (<i>VRS1</i>) homologs share conserved roles in growth repression.

Abstract

Crop engineering and de novo domestication using gene editing are new frontiers in agriculture. However, outside of well-studied crops and model systems, prioritizing engineering targets remains challenging. Evolution can guide us, revealing genes with deeply conserved roles that have repeatedly been selected in the evolution of plant form. Homologs of the transcription factor genes <i>GRASSY TILLERS1</i> (<i>GT1</i>) and <i>SIX-ROWED SPIKE1</i> (<i>VRS1</i>) have repeatedly been targets of selection in domestication and evolution, where they repress growth in many developmental contexts. This suggests a conserved role for these genes in regulating growth repression. To test this, we determined the roles of <i>GT1</i> and <i>VRS1</i> homologs in maize (<i>Zea mays</i>) and the distantly related grass brachypodium (<i>Brachypodium distachyon</i>) using gene editing and mutant analysis. In maize, <i>gt1; vrs1-like1</i> (<i>vrl1</i>) mutants have derepressed growth of floral organs. In addition, <i>gt1; vrl1</i> mutants bore more ears and more branches, indicating broad roles in growth repression. In brachypodium, <i>Bdgt1; <i>B</i>dvrl1</i> mutants have more branches, spikelets, and flowers than wild-type plants, indicating conserved roles for <i>GT1</i> and <i>VRS1</i> homologs in growth suppression over <i>ca.</i> 59 My of grass evolution. Importantly, many of these traits influence crop productivity. Notably, maize <i>GT1</i> can suppress growth in arabidopsis (<i>Arabidopsis thaliana</i>) floral organs, despite <i>ca</i>. 160 My of evolution separating the grasses and arabidopsis. Thus, <i>GT1</i> and <i>VRS1</i> maintain their potency as growth regulators across vast timescales and in distinct developmental contexts. This work highlights the power of evolution to inform gene editing in crop improvement.