The maize Mucronate mutation is a deletion in the 16-kDa γ-zein gene that induces the unfolded protein response
Mucronate (Mc) was identified as a dominant maize (Zea mays L.) opaque kernel mutation that alters zein storage protein synthesis. Zein protein bodies in Mc endosperm are misshapen and are associated with increased levels of ER Lumenal Binding Protein (BiP). Using GeneCallingTM to profile endosperm RNA transcripts, we identified an aberrant RNA in Mc that encodes the 16-kDa γ-zein protein. The transcript contains a 38-bp deletion (nucleotides 406–444 after the initiation codon) that creates a frame-shift mutation and an abnormal sequence for the last 63 amino acids. Genetic mapping revealed the Mc mutation is linked with the locus encoding the 16-kDa γ-zein, and two-dimensional gel electrophoresis confirmed the 16-kDa γ-zein protein is altered in Mc. The mutant protein exhibited changes in solubility properties and co-immunoprecipitated with the molecular chaperone, BiP. Transgenic maize plants expressing the Mc 16-kDa γ-zein manifested an opaque kernel phenotype with enhanced levels of BiP in the endosperm, similar to the Mc mutant. Unlike the wild-type protein, the Mc 16-kDa γ-zein interacted only weakly with the 22-kDa α-zein when expressed in the yeast two-hybrid system. These results indicate that the Mc phenotype results from a frame-shift mutation in the gene encoding the 16-kDa γ-zein protein, leading to the unfolded protein response in developing endosperm.
Document Type: Research Article
Affiliations: 1: Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA 2: Department of Botany, North Carolina State University, Raleigh, NC 27695, USA and 3: Pioneer HiBred International, a DuPont Company, 7300 NW 62nd Ave, Johnston, IA 50131-1004, USA
Publication date: November 1, 2006