Abstract: Particular aspects show that DWF1 is a Ca2+/calmodulin-binding protein, and this binding is critical for function. Molecular/genetic analysis using site-directed and deletion mutants revealed that loss of calmodulin binding abolished the function of DWF1 in planta, whereas partial loss of calmodulin binding resulted in a partial dwarf phenotype in complementation studies, providing direct proof that Ca2+/calmodulin-mediated signalling has a critical role in controlling the DWF1 function. Furthermore, DWF1 orthologues from other plants have a similar Ca2+/calmodulin-binding domain, indicating that Ca2+/calmodulin regulation of DWF1 and its homologues is common, and broadly applicable in plants. Methods for generating size-engineered crops are provided by altering the Ca2+/calmodulin-binding property of their DWF1 orthologues.