1.Institute of Crop Sciences, Chinese Academy of Agricultural Sciences/National Key Facility for Crop Gene Resources and Genetic Improvement;2.State Key Laboratory for Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University
The Fundamental Research Funds for Excellent Young Scientist of CAAS (Y2017JC02)
谷蛋白是稻米贮藏蛋白的主要组分，其含量和组成直接影响稻米的各项品质指标和营养价值。在水稻胚乳中，谷蛋白首先在内质网中以57 kDa前体的形式合成，之后经由复杂的细胞学转运途径到达蛋白贮藏液泡后完成切割和沉积。尽管经过数十年的研究，已经分离克隆了10余个谷蛋白合成、转运和沉积的关键基因，但其分子调控网络尚有待完善。本研究从日本晴组培突变体库中鉴定了一个谷蛋白57H突变体T360。遗传分析表明，突变体T360的表型由一对单隐性核基因控制，图位克隆将目标基因锁定在第4号染色体248.9 kb的物理区间内。定位区间含有一个编码β型液泡加工酶的基因OsVPE1，负责谷蛋白的加工成熟。测序分析未发现OsVPE1基因组水平上存在差异，但RT-qPCR实验证实OsVPE1基因表达量显著下调。转基因结果表明，野生型OsVPE1的基因组能够恢复突变体表型，初步的甲基化检测未发现OsVPE1基因存在甲基化缺陷。该研究为OsVPE1基因表达调控机制提供了重要的遗传材料。
Glutelin is the main component of rice storage proteins, and its content and composition directly affect the rice grain quality and nutrition. In rice endosperm, glutelin is synthesized in the form of 57 kDa precursor in endoplasmic reticulum, followed by the cleavage and deposition in the storage vacuoles through complex cytological transport pathways. Although 10 key genes required for glutelin synthesis, transport and deposition have been identified, their molecular regulatory network remains dissected in details. In this study, we identified a glutelin precursor accumulation mutant named T360 from the Nipponbare tissue-cultured mutagenesis population. Genetic analysis showed that the mutant phenotype of T360 was controlled by a single recessive nuclear-encoded gene. Through map-based cloning the candidate gene in this mutant was delimited to a 248.9 kb physical interval on chromosome 4. Gene annotation analysis showed that OsVPE1 coding β-vacuolar processing enzyme found in the genetic region is a candidate responsible for the maturation of glutelins. No mutation in OsVPE1 at the genome sequence was identified, whereas its expression was significantly down-regulated. Expressing the wild-type OsVPE1 genomic sequence in the mutant is able to complement the mutant phenotype, despite of no difference on DNA methylation revealed in wild type and T360. Altogether, this work provided an important mutant to decipher the molecular regulation mechanism of the VPE1 gene in rice.