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Free Content The vacuolar processing enzyme OsVPE1 is required for efficient glutelin processing in rice

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Rice (Oryza sativa L.) accumulates prolamines and glutelins as its major storage proteins. Glutelins are synthesized on rough endoplasmic reticulum as 57-kDa precursors; they are then sorted into protein storage vacuoles where they are processed into acidic and basic subunits. We report a novel rice glutelin mutant, W379, which accumulates higher levels of the 57-kDa glutelin precursor. Genetic analysis revealed that the W379 phenotype is controlled by a single recessive nuclear gene. Using a map-based cloning strategy, we identified this gene, OsVPE1, which is a homolog of the Arabidopsis βVPE gene. OsVPE1 encodes a 497-amino-acid polypeptide. Nucleotide sequence analysis revealed a missense mutation in W379 that changes Cys269 to Gly. Like the wild-type protein, the mutant protein is sorted into vacuoles; however, the enzymatic activity of the mutant OsVPE1 is almost completely eliminated. Further, we show that OsVPE1 is incorrectly cleaved, resulting in a mature protein that is smaller than the wild-type mature protein. Taken together, these results demonstrate that OsVPE1 is a cysteine protease that plays a crucial role in the maturation of rice glutelins. Further, OsVPE1 Cys269 is a key residue for maintaining the Asn-specific cleavage activity of OsVPE1.
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Keywords: OsVPE1; cysteine protease; glutelins; rice (Oryza sativa L.); seed storage proteins; vacuolar processing enzyme

Document Type: Research Article

Affiliations: 1: National Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing 210095, China 2: National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China

Publication date: May 1, 2009

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