FUL1 is a key regulator of grain morphology, stem development, and other shoot characteristics in Sorghum bicolor

The AP1/FUL-like family is known to be one of the key gene families driving floral development and flowering time across plants, playing a central role in grain yield and plant architecture, however the species-specific function has yet to be characterised in sorghum. This study used CRISPR/Cas9 to characterize SbFUL1 's role in sorghum through comprehensive phenotypic and molecular analysis. Here it was demonstrated that mutant lines exhibited significant delays to flowering time. Quantitative phenotypic assays also revealed alterations to seed morphology and inflorescence architecture, consistent with previously reported FUL1 functions across other plant species. Notably, mutants displayed novel pleiotropic effects to stem morphology, not previously associated with FUL1 genes, including changes in stem structure and integrity. DAP-seq analysis identified potential SbFUL1 binding sites in genes involved in pectin biosynthesis and cell wall remodelling pathways, providing a putative molecular mechanism for the observed phenotypes. These findings confirm the functional conservation of FUL1 in sorghum flowering time and floral development, while also revealing broader pleiotropic effects than what has been previously recognised. This study demonstrates the value of holistic phenotypic approaches in gene characterisations and highlights opportunities for crop improvement through harnessing the floral regulatory genes with expanded functional roles.