Phytocalpain Defective Kernel 1 Is a Novel Arabidopsis Growth Regulator Whose Activity Is Regulated by Proteolytic Processing

• Published in: The Plant cell 2008-10, Vol.20 (10), p.2619-2630
• Main Authors: Johnson, Kim Leonie, Faulkner, Christine, Jeffree, Chris Edward, Ingram, Gwyneth Christina
• Format: Article
• Language: English
• Subjects: Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - analysis; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - genetics; Arabidopsis Proteins - physiology; Calpain - analysis; Calpain - chemistry; Calpain - genetics; Calpain - physiology; Cell Membrane - enzymology; Cell membranes; Cell Proliferation; Cytoplasm - enzymology; Developmental biology; Endoplasmic Reticulum - enzymology; Enzyme Activation - physiology; Epidermal cells; Genetic Complementation Test; Green Fluorescent Proteins - analysis; Growth regulators; Leaves; Meristem - enzymology; Meristem - growth & development; Mesophyll cells; Mutation; Phenotype; Phenotypes; Plant cells; Plant epidermis; Plant growth regulators; Plant Leaves - genetics; Plant Leaves - growth & development; Plant Leaves - metabolism; Plants; Protein Structure, Tertiary; Recombinant Fusion Proteins - analysis
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.108.059964

The role of the unique plant calpain Defective Kernel 1 (DEK1) in development has remained unclear due to the severity of mutant phenotypes. Here, we used complementation studies of the embryo-lethal mutant to dissect DEK1 protein behavior and to show that DEK1 plays a key role in growth regulation in Arabidopsis thaliana. We show that although full-length DEK1 protein localizes to membranes, it undergoes intramolecular autolytic cleavage events that release the calpain domain into the cytoplasm. The active calpain domain alone is not only necessary for DEK1 function but is sufficient for full complementation of dek1 mutants. A novel set of phenotypes, including leaf ruffling, increased leaf thickness, and abnormalities of epidermal cell interdigitation, was caused by expression of the constitutively active calpain domain. This analysis of the novel phenotypes produced by DEK1 under- and overexpression, as well as DEK1 subcellular localization and protein processing, has revealed a fundamental role for DEK1-mediated signaling in growth regulation.