南京农业大学等处的研究人员从分子水平揭示了引起水稻谷蛋白前体巨增突变性状的分子机理，阐述了该基因在谷蛋白合成、积累中的地位，利用该突变体及其基因标记可为低谷蛋白水稻品种选育提供材料和分子育种的基础。这一研究成果公布在Plant Journal杂志上。
水稻种子在胚乳中积累大量的储藏蛋白，约占籽粒干重的8%%—10%%，其中谷蛋白占70%%—80%%，醇溶蛋白占18%%—20%%。提高种子的谷蛋白含量并降低种子的醇溶蛋白含量将会提高稻米的营养价值，但是对患有肾脏病和糖尿病的人来说，谷蛋白的大量吸收将会导致病情的恶化。因此，深入研究水稻储藏蛋白合成、积累的分子机制对培育满足不同人群需求的蛋白含量的水稻品种具有重要意义。
在“973”、“863”以及国家自然科学基金等支持下，由万建民指导课题组通过对一个自然变异的水稻谷蛋白突变体OsVPE1基因的图位克隆和功能分析，发现突变体和野生型间在该基因上只有一个核苷酸的差异，导致了突变体中OsVPE1蛋白的269位由Cys突变为Gly，功能互补试验证实了OsVPE1就是突变基因。该基因的表达模式和表达水平在水稻日本晴和W379间虽无显著差异，亚细胞定位结果显示突变的蛋白亦分选进入液泡中。但酶活性测定显示，突变体发育胚乳中Asn特异剪切活性不到日本晴中的10%%，Western杂交显示，日本晴胚乳中该蛋白能进行正确的自我剪切成熟，形成正常的蛋白形式；而突变体胚乳中的OsVPE1（C269G）大都以前体的形式存在，其成熟时剪切发生了错误，形成的蛋白分子量小于日本晴中的正常蛋白，导致其功能丧失。（生物谷Bioon.com）
生物谷推荐原始出处：
The Plant Journal 19 Jan 2009 DOI：10.1111/j.1365-313X.2009.03801.x
The vacuolar processing enzyme OsVPE1 is required for efficient glutelin processing in rice
Yihua Wang 1 , Susong Zhu 2 , Shijia Liu 1 , Ling Jiang 1 , Liangming Chen 1 , Yulong Ren 1 , Xiaohua Han 1 , Feng Liu 1 , Sulan Ji 1 , Xi Liu 1 and Jianmin Wan 1,2,*
1 National Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing 210095, China , and 2 National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China
ABSTRACT
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.
