Ca²⁺/calmodulin is critical for brassinosteroid biosynthesis and plant growth

• Published in: Nature (London) Vol. 437; no. 7059; pp. 741 - 745
• Main Authors: Du, L, Poovaiah, B.W
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 29.09.2005; Nature Publishing Group
• Subjects: Amino Acid Sequence; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; binding capacity; binding proteins; Biological and medical sciences; biosynthesis; brassinosteroids; calcium; Calcium - metabolism; calmodulin; Calmodulin - metabolism; Fundamental and applied biological sciences. Psychology; Genetic Complementation Test; Growth regulators; Immunoprecipitation; Metabolism; Molecular Sequence Data; Mutation - genetics; Phenotype; plant growth; Plant Growth Regulators - biosynthesis; Plant physiology and development; plant proteins; Protein Binding; Protein Structure, Tertiary; signal transduction; Space life sciences; Steroids - biosynthesis; Calcium; Growth; Biosynthesis; Genetic determinism; Arabidopsis thaliana; Signal transduction; Brassinosteroid; Cruciferae; Dicotyledones; Angiospermae; Plant growth substance; Spermatophyta; Mutation; Calmodulin; Non-programmatic
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature03973

Brassinosteroids are plant-specific steroid hormones that have an important role in coupling environmental factors, especially light, with plant growth and development. How the endogenous brassinosteroids change in response to environmental stimuli is largely unknown. Ca²⁺/calmodulin has an essential role in sensing and transducing environmental stimuli. Arabidopsis DWARF1 (DWF1) is responsible for an early step in brassinosteroid biosynthesis that converts 24-methylenecholesterol to campesterol. Here we show that DWF1 is a Ca²⁺/calmodulin-binding protein and this binding is critical for its function. Molecular genetic analysis using site-directed and deletion mutants revealed that loss of calmodulin binding completely abolished the function of DWF1 in planta, whereas partial loss of calmodulin binding resulted in a partial dwarf phenotype in complementation studies. These results provide direct proof that Ca²⁺/calmodulin-mediated signalling has a critical role in controlling the function of DWF1. Furthermore, we observed that DWF1 orthologues from other plants have a similar Ca²⁺/calmodulin-binding domain, implying that Ca²⁺/calmodulin regulation of DWF1 and its homologues is common in plants. These results raise the possibility of producing size-engineered crops by altering the Ca²⁺/calmodulin-binding property of their DWF1 orthologues.