Loss of DELLA function reduces plant height and reveals divergent regulation of DELLA activity in maize

DELLA proteins are central repressors of gibberellin (GA) signaling in plants. In Arabidopsis and rice, gain- and loss-of-function mutations in DELLA genes confer semidwarf and slender phenotypes, respectively. However, studies in Arabidopsis and tomato have suggested that a subset of GA responses can be mediated through DELLA-independent pathways. To date, no loss-of-function DELLA mutant has been characterized in maize. Here, we report the identification of a novel dominant maize DELLA mutant, D8-3 , which exhibits a dwarf phenotype associated with reduced cell elongation. We show that an E602K amino acid substitution in the C-terminal GRAS domain markedly increases D8 protein stability. To investigate DELLA function in maize, we generate single and double loss-of-function mutants of the two maize DELLA homologs using genome editing. In contrast to observations in rice, disruption of DELLA function does not result in a slender growth phenotype in maize. Transcriptome analyses further reveal that expansin genes, which were strongly induced in the rice slender rice1 ( slr1 ) mutant, are not significantly upregulated in maize DELLA loss-of-function mutants. Together, our findings uncover both conserved and maize-specific mechanisms governing DELLA regulation and function, providing new insights into the diversification of GA signaling pathways in plants.