Zhang Zhiyong, Yang Jun, Wu Yongrui
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
Plant Cell. 2015 Apr;27(4):1162-72. doi: 10.1105/tpc.15.00035. Epub 2015 Apr 21.
Maize (Zea mays) zeins are some of the most abundant cereal seed storage proteins (SSPs). Their abundance influences kernel hardness but compromises its nutritional quality. Transcription factors regulating the expression of zein and other SSP genes in cereals are endosperm-specific and homologs of maize opaque2 (O2) and prolamine-box binding factor (PBF). This study demonstrates that the ubiquitously expressed transcription factors, O2 heterodimerizing proteins (OHPs), specifically regulate 27-kD γ-zein gene expression (through binding to an O2-like box in its promoter) and interact with PBF. The zein content of double mutants OhpRNAi;o2 and PbfRNAi;o2 and the triple mutant PbfRNAi;OhpRNAi;o2 is reduced by 83, 89, and 90%, respectively, compared with the wild type. The triple mutant developed the smallest zein protein bodies, which were merely one-tenth the wild type's size. Total protein levels in these mutants were maintained in a relatively constant range through proteome rebalancing. These data show that OHPs, O2, and PBF are master regulators of zein storage protein synthesis, acting in an additive and synergistic mode. The differential expression patterns of OHP and O2 genes may cause the slight differences in the timing of 27-kD γ-zein and 22-kD α-zein accumulation during protein body formation.
玉米（Zea mays）醇溶蛋白是一些最为丰富的谷类种子贮藏蛋白（SSPs）。它们的丰度影响籽粒硬度，但会损害其营养品质。调控谷类醇溶蛋白和其他贮藏蛋白基因表达的转录因子是胚乳特异性的，是玉米不透明2（O2）和醇溶蛋白盒结合因子（PBF）的同源物。本研究表明，普遍表达的转录因子O2异二聚化蛋白（OHPs）特异性调控27-kDγ-醇溶蛋白基因的表达（通过结合其启动子中的类O2盒）并与PBF相互作用。与野生型相比，双突变体OhpRNAi;o2和PbfRNAi;o2以及三突变体PbfRNAi;OhpRNAi;o2的醇溶蛋白含量分别降低了83%、89%和90%。三突变体形成的醇溶蛋白小体最小，仅为野生型大小的十分之一。通过蛋白质组再平衡，这些突变体中的总蛋白水平保持在相对恒定的范围内。这些数据表明，OHPs、O2和PBF是醇溶蛋白贮藏蛋白合成的主要调节因子，以累加和协同的方式发挥作用。OHP和O2基因的差异表达模式可能导致在蛋白体形成过程中27-kDγ-醇溶蛋白和22-kDα-醇溶蛋白积累时间上的细微差异。
